The Foundry: Blowing Smoke

In the last post, we saw a fire actually burning in the foundry. The concrete has set, and doesn’t fall apart while being used. After researching other designs, and using some logic, we figured we need to force more air into the system. As we designed previously, there is a large 30mm hole on the side of the forge to allow air into the fire. Unfortunately, this doesn’t seem to provide the amount of air we need to get the desired heat. We have tried a number of ways to force air into the hole, with varying success. First we literally blew into it, like you would a campfire, and it works well, but soon you start to really hyperventilate, and it’s not good. The next idea was to take a chopping board (but any board will do) and flapped it, forcing air towards the hole. This worked much better than simply blowing. Lots of air fuels the fire, and it burns really hot. The big downside is that it wastes most of the air produced, and creates some interesting smoke patterns that seem to be inefficient. Either way, it is a good cheap way to improve the forge performance.

First Tests
The foundry during its first fire, not particularly hot.

The method we eventually used to force air into the system was in the form of a fan. Before I start this section, it comes with a warning, you need to wear goggles if you try this, as will be explained. You have been warned. The initial fan was in the form of an old hairdryer, bought from a charity shop for £3. Putting it right up to the hole forced hot air directly into the hole, with very little waste air escaping. It worked very well, and the fire started to burn much hotter. It also meant we could control the amount of airflow by using the switches on the hairdryer, or simply moving it further away.

Forcing air into the forge
Forcing air into the forge using a hairdryer, the fire is visibly hotter.

Two issues came up while using this method of airflow. The first big problem is the mass of air being forced into the hole needs to go somewhere. The only place it can go is straight up, and as we don’t have a lid it just fires ash into the air. This is dangerous if gloves and goggles aren’t being worn. This ash can be hot and can take some of that fuel and heat away from the forge. A lid will fix this, and that will be covered in the next post. For this test we kept it at a low fan speed, and found a nice point where we weren’t firing ash into the air, but still giving lots of air to the fire. The second problem was that the hairdryer started getting really hot, and the plastic began to melt. Essentially this means it was too close to the fire, but if you move the fan away then the air just misses. To fix this we found a 30mm diameter iron pipe, and attached the hairdryer to it. This allowed the air to be funneled in with the fan unit being further away from the forge.

The fire burning
The fire burning with a steel tin on top to stop the ash flying out.

So what have we learnt from this fire? We need a lid. This will be a topic of further posts, but for now we know we can produce a hot fire, and the air going into the fire can be controlled. Thanks for reading, and hope to come with another update soon.

Halfpenny Bridge: The Bridge Over Nothing

If you walk down Union street in Plymouth, just before you come to Devonport you will come across what looks like a bridge. Called Stonehouse Bridge, it comes from a time when Plymouth had a very large river/lake separating Devonport and Plymouth-Town. Originally to get across the creek to what was then known as Plymouth-Dock, you had to take the pedestrian ferry, or go all the way up to Mill bridge. So in 1767 Lord Mount Edgcumbe, who was lord of the manor of East Stonehouse, and Sir John Saint Aubyn, Lord of the Manor of Stoke Damerel, obtained an act of Parliament authorising construction of a bridge. The idea was to allow for a more direct link between Plymouth-Dock and East Stonehouse. It made sense when in the Act they described the old ferry as ‘narrow and could only be used by foot passengers’.

Stonehouse Bridge, Plymouth, engraved by W.B. Cooke 1836 Clarkson Frederick Stanfield 1793-1867

The man who designed the Eddystone Lighthouse, that now stands on Plymouth Hoe, John Smeaton, was invited to design the bridge. The bridge charged a toll to get across it, like many bridges of the time, and it was fixed by the act of parliament. It cost 2d return for a 1-horse drawn vehicle, 3d for  a 2 horse vehicle, and 6d for wagons drawn by more than 2 horses. The nickname ‘Halfpenny Bridge’ was from the halfpenny it cost for pedestrians to cross, also it was sometimes pronounced ‘Ha’penny Bridge’. Interestingly it absolved the owners from paying any public or parochial rate or tax.

The old 5 horse car at the halfpenny gate

Opened in 1773, the approach to it was via Stonehouse lane (now known as King Street) and the High Street, rather than Union Street. in 1775 the first carriages began to be hired between Plymouth and Plymouth Dock, over the new bridge. Carriages were popular but Stonehouse lane was described as ‘ruinous’ and a new road was needed. A further Act of Parliament was obtained in 1784 to create the Stonehouse Turnpike Trust. In 1815  Union Street was finally opened, as a turnpike, the users paid a toll to use the bridge, that went to the upkeep of it.  So users now had to pay for the bridge and the road leading up to it. Turnpikes were very popular in the 18th and 19th century and are basically a toll road. In 1828 the bridge was raised while Devonport hill was lowered. This meant that hackney carriages could now be used to provide a route between Plymouth and Devonport the following year.

Stonehouse Bridge from Richmond Walk.

Both Plymouth and Devonport tried many times to purchase the gate, but the bridge, along with Stonehouse Mill bridge were sold in February 1890 to the General Tolls Company Ltd for £122,000. The company (with the Earl of Mount Edgcumbe and Lord Saint Levan had shares in) was registered on February 12th 1980. The idea was for the owners to collect the tolls rather than auction them, which was more common at the time. From October of 1917, servicemen and nurses could get across the bridge for free.

Stonehouse creek before being filled in, from the bridge

After long negotiations, an Act of Parliament in 1923 allowed Plymouth Town Council to buy the toll rights for £100,000. This meant that the Council could have charged tolls and collected than money for up to ten year. Instead, on April 1st 1924, the Mayor, Mr Solomon Stephens, and council visited all the toll houses and declared them free.

Stonehouse Bridge Freeing Ceremony, 1924 looking towards Devonport. From a postcard

The upper end of the creek, near the Pennycomequick, was known towards the end of the 19th century as Deadlake. St Barnabas Terrace, a road now adjacent to the park, was marked on 19th century maps of the area as Deadlake Lane. Toward the end of the 19th century, culverts were made to channel the streams that ran into deadlake, and the swampland was filled in with rubble from the quarries at Oreston and Cattedown. To celebrate queen Victoria’s reign, Victoria Park, along with the park-keeper’s lodge, was formally opened to the public in 1903.

Looking down the filled in fields, towards Stonehouse

Between Mill Bridge and Stonehouse Bridge, the creek was filled in in 1972, when 600,000 tons of ballast and rubble were used to create 19 acres of land. Now a set of pitches for Devonport High School for Boys (previously the royal naval hospital) and the pitch for Devonport RFC. When you walk along it you can see some areas, especially close to the bridge where all the rubble has been added. On the water side of the bridge you can see where the arches have been filled up. Stonehouse bridge is now more of a dam, but one with some important history for Plymouth.

Halfpenny Bridge, on the side of the creek

Four Bit Carry Adder/Subtractor Circuit

After creating my 1 bit full adder design found in a previous post, I decided to go for something a little more complicated. I wanted to prove to myself that the ripple carry system worked, so the obvious choice is to make a multi bit device. 4 bits seemed like a good amount, it’s a value used in some early ALU’s so it can be used in a future project. To make it more interesting I added in the ability to make the device a Subtractor at the same time. When you look at the schematic, it only requires one more device per adder, so it’s not even an expensive thing to implement, but adds lots of functionality. As with the 1 bit adder, I have attempted to build this adder using only single logic chips.

4 bit adder-subtractor circuit

The first stage is to know the logic circuit, its widely known and can be found pretty easily all over the web. I’m not going to explain how it’s created (I can always make a separate post on that) but I can describe how to use it. The aim is for the device to take two 4 bit inputs (0 – 15), along with a carry from another adder. So the adder needs to be able to output a value between 0 and 31. In binary this can be shown as 5 bits, so we have 2 outputs. This the S output is a 4 bit bus, and the Co output bumps this up to the 5 bits we need to make 31. A truth table can be made for this but it would be 32 lines long, so too much for this post. You could regard it as a personal challenge if you want to attempt it on your own.

So I got onto Altium and made a schematic of this circuit using some of the low voltage 7400 LVC series individual logic gates that I used on the previous adder I made. They come in SOT23-5 packages which are leaded a nice size to solder. Plus they are a size where it’s possible to probe the pins fairly easily. Luckily Altium shows the components as their logic symbols. Below I have shown the first two adders, the third and fourth are basically the same as the second one, which is the idea of the ripple carry adder.

The first two adders of the four found on the board

I also added a few LEDs to show what parts are on and off. This means the user can see the inputs and outputs. These LEDs run off the 5V input voltage, and have 220Ω current limiting resistors in series with them. Also, I have put in some 0.1 inch header pins so it can be attached into a breadboard and maybe even a micro.

The LEDs for the carry bits and outputs
The LEDs for the input bits

As a base of my circuit, I have decided on a double sided 100mm x 100mm board. This is quite big as you can see for the circuit I have made, but gives plenty of space for a soldering iron to get access. As well as this, it gives a nice amount of space for multimeter probes. I also tried to keep the individual logic chips in a similar arrangement as the schematic. This is meant to be used as a learning device, so it’s useful for the chips to line up with the diagram. The header pins for the inputs and outputs are placed on opposite sides of the board to make it more obvious for the user to see it. And the pins have designators written on the board so the user can see what each pin does. The input and output busses are placed in fairly logical places, and grouped together. There is no point having all the A inputs intertwined with the B inputs. The pins for the power and ground are on opposite sides with their own headers, only one needs to be connected for it to work. The LEDs that are directly attached to the pins are placed closer to the logic circuitry, but labeled clearly on the silkscreen. Most of the routing to the LEDs is on the underside of the board, else the top could get confusing. All the designators for components have been made half the normal size due to the small amount of parts used in the project. The below images show the PCB layout I created with the top copper being red, bottom copper being blue, and the silkscreen shown in yellow.

Top Copper

As you might be able to see, I have tried to keep all the power on the bottom side of the board. This leaves lots of space for the logic signals on the top, where the user is more likely to see. As you can see, most of the inputs and outputs of the circuit are also on the bottom side. This is because the way the busses work and input into the adder needs lots of crossing over and would add confusion into the design. This is why labels were used instead.

Bottom Copper

To make it easier to see, I made a larger image of the first and last adder in the series. As you can see, the only real difference in them is that the first has the add/subtract input shown by an LED, whereas the last shows the carry from the previous adder (C0). This is because the A/D bit is attached to all the adders, but the first bit doesn’t have a carry bit input. The carry on that adder is the input for the A/S. It serves the function of inverting the first bit, so that it works like 2’s complement when in subtract mode.

The layout of the first adder in the series
The layout of the last adder in the series

As noted above I used 7400 LVC series logic gates. The SOT23-5 package chips have the suffix of “BVD”. See the datasheets for each of the devices for more information. I have written a simple bill of materials below:

12x SN74LVC1G86DBVT – XOR gate
8x SN74LVC1G08DBVT – AND gate
4x SN74LVC1G32DBVT – OR gate
17x DO-214 LED’s
17x 0805 220Ω resistors
6x 5-pin 0.1″ header pins

The main downside to this type of adder is that is is very slow. Especially when you get to high bit amounts that you are trying to add. This adder will take at least 4 times as long as a single adder to add the two numbers together because the signal has to propage through 4 full adders. This problem is known as propagation delay, each logic chip will take a very short time to compute the output. Although this time is not perceivable by the human eye, if there are 100’s of logic gates in a row, then the delays start to add up and be a problem. If this circuit is to be used in a computer, it could need to make calculations thousands, or maybe millions of times a second, and a carry bit adder is not generally good at that. There are other, faster adders that I will show in a future post.

Why James Webb Was so Important

NASA Administrator James E. Webb
NASA Administrator James E. Webb. This was his official NASA photograph

There are not many people who know off the top of their head who James Webb is, even many lovers of space may not know who he was. Yet they are about to launch the James Webb Space Telescope into space to replace Hubble. James Webb wasn’t an engineer, or a physicist, or even really an academic; he was a lawyer and politician. He turned a small government research department into an organisation that had links to almost every state, and had control of 5% of the US federal budget. Webb’s NASA controlled the jobs of half a million workers across America, and he introduced new working practices and management techniques that are still used today.

If you were to go out and read the biographies of the astronauts, or histories of spaceflight, Webb doesn’t really come up. He was portrayed as just a bureaucrat in Washington, funnelling orders down the chain, living the politician life. In this new age of spaceflight, we see the Apollo years as some sort of poetic story, with NASA being the figurehead of the battle to win space against the evil russians. In 1961 though, America did not follow this narrative, nobody in America cared about space, least of all the brand new president, John F Kennedy. When he set up his first reshuffle of the cabinet they simply could not get anyone to run NASA, they asked 18 high level politicians, and everybody said no, space was a dead end job, and NASA was just a collection of squabbling mission centres. Eventually, JFK’s vice president, Lyndon B. Johnson suggested Jim Webb, a guy who had worked under the Roosevelt administration and had some experience with private businesses. When asked, by JFK personally, Webb agreed to run NASA, as long it was the way he wanted it. JFK, desperate for an administrator gladly agreed.

shaking hands with JFK
President Kennedy shakes hands with NASA Administrator James Webb

There had been heavy opposition to the idea of manned spaceflight. Up to this point, the head of the President’s Science Advisory Committee, Jerome Wiesner, had issued a critical report on project mercury. Kennedy, as a senator he had openly opposed the space program and wanted to terminate it. Kennedy put his vice president LBJ as the head of the National Aeronautics and Space Council because he had helped create NASA, but it was mainly to get him out of the way. Although Kennedy did try and reach out for international cooperation in space in his state of the union address in January 1961, he got nothing from Khrushchev. Kennedy was poised to dismantle the effort for space, purely because of the massive expense.

The space Council
Vice President Lyndon B. Johnson (seated, center) presides over a meeting of the National Aeronautics and Space Council.

He began his NASA administration on February 14th 1961. A month later on April 12th, Yuri Gagarin became the first man to orbit the earth. Reinforcing some fears that America was being left behind in a technological competition with the Soviet Union, America suddenly cared about space. Kennedy made a U-turn and space sped to the top of the list.  This lead to Kennedy making his famous speech on May 21st where he spoke those famous words “we will put a man on the moon before the decade is out”. Kennedy wanted to take lead in the space race. Suddenly, putting a man on the moon was the number one priority.

Kennedy Talking to Congress
MAy 1961, Kennedy proposes landing a man on the moon to congress. LBJ and Sam Rayburn sit behind him.

This meant that James Webb just got handed the opportunity to run the biggest single project the country had ever seen. Webb was told to go back to his engineers and figure out how much it will cost to get to the moon. His engineers came up with the number of $10 billion (a scary big number in the 1960’s), and sheepishly told Webb, expecting to be told to make cuts and slashes to the plan. Instead he told them to go higher, because he knew problems would come their way, and extra money will need to be spent, so they come back with the figure of $13 billion. Webb accepts the number, and goes to congress and tells them he needs $20 billion over the next 7 years. Jaws hit the floor, but he used this political knowledge to get a huge amount of leverage.

The key leverage he had was jobs, and he knew it. At its height, NASA employed half a million people in some form, that’s roughly the number of people living in Wyoming. The two biggest investments were in Cape Canaveral, FL and Houston, TX. The most controversial was the Manned Spaceflight Centre in Houston, donated by Rice University. Originally based in Langley Virginia, and named the Space Task Group, the senator didn’t care much for space. The entire operation was moved to Houston, LBJ’s home state. It was central, and had good universities surrounding it. There were many Texas based representatives in the space political landscapes at that time, such as Sam Rayburn, the speaker of the House of Representatives.

Johnson Space Centre
Manned Spaceflight Centre, Texas, one of the biggest employers in Texas for a long time. with over 3000 federal workers, and 100 buildings

One thing that Webb understood was what NASA needed to run. He implemented a very flat organisational structure, with very few middle managers. Webb was the very top, controlling Washington. He also had the head of NACA (precursor to NASA) Hugh L. Dryden as an associate director. He had overseen the development of the x-15, and understood the technical needs of Apollo. Also Robert Seamans, also an associate director, acted as the general manager of NASA, and oversaw the everyday running of the program. Using a team of people, each with their own particular strengths helped NASA, especially in the early growth years, much more so than any one of them could achieve on their own.

Webb in a Gemini Trainer
Webb in a Gemini Trainer

Part of what James Webb did, to the dislike of congress, was to invest in academia, specifically universities. $30 million dollars a year was put into the Universities Development Fund. A fund designed to help students get into engineering, and to develop talent, skills, and academics that could not only work for NASA, but help the science behind it. As it was taken from a fund that congress had no control over, the money continued to help 7000-8000 students a year get through university at a time where NASA needed engineers. Webb believed that NASA was more than just the one shot to the moon, and frequently fought with the presidents on that fact. He wanted NASA, and space exploration to benefit science, engineering and even society. He believed that this project could fix other problems not even related to space, such as poverty and disease. The management style of NASA, and the way these big projects were handled showed the impossible could be achieved. He frequently lectured on this subject, and universities became an important part of NASA.

Launch_Complex_34_Tour
Webb, Vice President Lyndon Johnson, Kurt Debus, and President John F. Kennedy receive a briefing on Saturn I launch operations

There was huge pressure from washington to spend all of NASA’s budget purely on the Apollo moonshot. Webb was instrumental in making sure that NASA and spaceflight was more than that. be made sure other projects like the Mariner and Pioneer space programs happened, and that JPL still functioned even with a terrible track record at the time. At the time, the academic community worked with NASA, in large part because of the importance Webb put on furthering science. Webb would frequently lecture at universities, and teach about the management styles that made NASA was. Unfortunately, some in Washington didn’t care for the extra spending, especially the states that did not have a mission centre or any of the major manufacturing plants located there. So when the Apollo 1 fire happened, there were a small group that were willing to use it as a way to make changes.

Closeup of James E. Webb, National Aeronautics and space administration

The Apollo 1 fire was a very unfortunate accident, and a national tragedy. For some, it highlighted some major problems with the Apollo program and how it had been run by the major contractor North American Aviation. Committees were set up, and Webb suddenly went from running NASA to trying to defend it. During the inquests, NASA still ran, it continued to fix problems and aim for the moon. This was because James Webb was there defending it. Left to just take the heat, some believe (me included) NASA’s funding would have been significantly cut, and we may have never got to the moon. Webb stood up in Washington and fought hard for the continuation of the project, defending the decisions that his team had made. At the end of it, he had used up most of his political sway, and called in so many favours that NASA was safe for the time being, and that Apollo was possible.

Webb presents NASA’s Group Achievement Award to Kennedy Space Center Director Kurt H. Debus, while Wernher von Braun (center) looks on

At this point, Johnson had decided not to run for re-election, Webb felt that he should step down to allow Nixon to choose his own administrator. On October 7, 1968 he stepped down from office. To put that into perspective, Apollo 11 landed on the moon July 20th, 1969, barely a year later. Webb went on to be a part of many advisory boards and served as regent for the Smithsonian institute. He died in 1992, and was buried in Arlington National cemetery.

This post was inspired by reading the book: The Man Who Ran The Moon by Piers Bizony. For anyone interested in the subject of how Webb actually made his dealings, and a much more detailed account of how NASA became what it is, I recommend this book. He also did a Lecture on Webb that I found on YouTube where he tells the story really well.

 

The Foundry: The First Fire

Now it’s time to test the foundry, or at least the first version of it. This also has a benefit to it. Some others who have made this style of foundry have found this process helps the concrete to fully cure, and dry any leftover water still in the mixture. This process is pretty simple, most suggest using charcoal as the main fuel. We went down the local hardware store and they had a sale on charcoal briquettes. These are small and there are plenty of them, and fit nicely in the foundry. Light the fire in any way you are used to, we used fire lighters and some cheap kindling, also from the hardware store. If you don’t know how to light fires safely, find somebody who does.

First Tests
The foundry having its first fire, drying it out and seeing whether it can survive.

We didn’t use much to start with, this is meant to be a calm fire to help cure the concrete, and test it can deal with at least some hot temperatures. It was also to see how well it burnt with the air hole we put in. Main problems we found were that the air hole did not provide enough oxygen into the system, so the fire was slightly stinted. We tried blowing into the hole a few times, and the fire definitely got bigger, but it also sprayed ash into the air, so be very careful of that. We also noticed something most blogs talk about, lots of heat escapes from the top. With the foundry having such a big opening, very little of the heat is retained, and the fire has to work harder to keep the heat at a set level. A lid is often the best way to battle this.

The aftermath
The foundry after its first test and the ash was scraped out of it.

So what have we learnt from our first fire? We need a lid, and some way to force air into the hole. This will be a topic of further posts, but for now we know our concrete foundry can withstand the heat of a fire, and is now a little bit darker from all the ash. Thanks for reading, and hope to come with another update soon.

One Bit Adder Project

One thing that has always been interesting to me is using logic circuitry in electronics. It’s easy to implement something on a microcontroller in just a few lines of code, but the real challenge comes from making a boolean project using real logic gates. It’s something we all learn about if you have taken a basic computer science class, or even digital electronics. One of the first circuits you ever learn about is the adder. It’s pretty simple, teaches you how to cancel down boolean equations, and only has a few inputs and outputs. I have decided to try and make the circuit using real components, and see if I can get it to work.

full adder layout

The first stage is to know the logic circuit, its widely known and can be found pretty easily all over the web. I’m not going to explain how it’s created (I can always make a separate post on that) but I can describe how to use it. The aim is for the device to take two 1 bit inputs, along with a carry from another adder. So the adder needs to be able to output a value between 0 and 3. In binary this can be shown as 2 bits, so we have 2 outputs. The S output represents bit 1, and the Co output represents bit 2. Below is the truth table I used, if you want a little challenge, try and get the above circuit using boolean algebra.

A B Ci Co S
0 0 0 0 0
0 0 1 0 1
0 1 0 0 1
0 1 1 1 0
1 0 0 0 1
1 0 1 1 0
1 1 0 1 0
1 1 1 1 1

So I got onto Altium and made a schematic of this circuit using some of the low voltage 7400 LVC series individual logic gates. They come in SOT23-5 packages which are leaded and a nice size to solder. Plus they are a size where it’s possible to probe the pins fairly easily. Luckily Altium shows the components as their logic symbols.

1 bit adder 1 schematic

I also added a few LEDs to show what parts are on and off. This means the user can see the inputs and outputs. These LEDs run off the 5V input voltage, and have 220Ω current limiting resistors in series with them. Also, I have put in some 0.1 inch header pins so it can be attached into a breadboard and maybe even a micro.

1 bit adder 1 schematic

As a base of my circuit, I have decided on a double sided 50mm x 50mm board. This is quite big as you can see for the circuit I have made, but gives plenty of space for a soldering iron to get access. As well as this, it gives a nice amount of space for multimeter probes. I also tried to keep the individual logic chips in the same arrangement as the schematic. This is meant to be used as a learning device, so it’s useful for the chips to line up with the diagram. The header pins for the inputs and outputs are placed on opposite sides of the board to make it more obvious for the user to see it. The pins for the power and ground are on the same side on both headers. The LEDs that are directly attached to the pins are kept close to them, and the track is fairly obvious to show where the signal is from. The silkscreen labels which LED designates which input/output. All the designators have been made half the normal size due to the small amount of parts used in the project. The below images show the PCB layout I created with the top copper being red, bottom copper being blue, and the silkscreen shown in yellow.

1 bit adder 1 PCB top

As you might be able to see, I have tried to keep all the power on the bottom side of the board. This leaves lots of space for the logic signals on the top, where the user is more likely to see. As you can see, not all signals are on the top side due to circuit constraints, but signals that do swap over are generally short jump, and straight lines, This makes it more obvious where the tracks go without having to flip the board.

1 bit adder 1 PCB bottom

As noted above I used 7400 LVC series logic gates. The SOT23-5 package chips have the suffix of “BVD”. See the datasheets for each of the devices for more information. I have written a simple bill of materials below:

2x SN74LVC1G86DBVT – XOR gate
2x SN74LVC1G08DBVT – AND gate
1x SN74LVC1G32DBVT – OR gate
5x DO-214 LED’s
5x 0805 220Ω resistors
2x 5-pin 0.1″ header pins

How a Voltage Regulator Works: LM7805

Voltage regulators are one of the first electronic components you get introduced to as a hobbyist. Really useful when starting out, it simply takes a voltage that is too high, and reduces it down to a set voltage that you want, usually defined by the component. Solves the problem of having batteries or power supplies being a different voltage to the thing you are powering (such as your Arduino), and at as little as 50p from ebay they are easily acquired. Sounds like a great solution, but there is an issue, they are terribly inefficient. They are known to get very hot when used at high currents, and often need hefty heatsinks to stop the magic smoke from being released. To demonstrate why they get so hot we need to think about what happens during use. Remembering Kirchoff, the current going into a system is the same as the current going out of the system. If we use a simplified version of the regulator, the only thing this device changes is the voltage of the output. Due to the minimal current lost powering the circuit we assume the vast majority of power lost is in heat. Using the basic equation of:

Power (W) = Voltage (V) x Current (I)

So if we use an example of the LM7805 made by On Semiconductor (previously Fairchild) that can regulate 5V at 1A. It’s a pretty standard component, and is very typical of a voltage regulator.

If we use a 9V input the power going in is 9V x 1A = 9W.

The output power is 5V x 1A = 5W.

This means that there is 4W of power being dissipated from the regulator as wasted heat. This is a large amount when considering the size of the packages available. When thinking about problems excessive heat can cause in a circuit, it can quite easily damage itself and other components around it when not designed properly. It is why there are often big chunks of aluminium attached to the back of the components to act as a heat sink.

7805
7805 chip in a TO-220 package. Notice the heat sink on the rear with a screw mount.

This post isnt meant to dissuade you from using regulators, they have their place in electronic circuits, and are a great starting point. All electronic engineers need to have a broad understanding of the advantages and disadvantages of linear voltage regulators to be able to handle them properly.

How it Works

LM78xx schematic 2 coloured
Schematic of the silicon inside an LM78xx device, coloured relating to the function of each area.

The above schematic can be found on the datasheet, but it’s been coloured in to show the different sections of the circuit.

The most important component in the above schematic is Q16 (Red), it controls the current between the input and output, therefore the voltage. It is placed in a darlington pair configuration with Q15 (Orange). In this configuration Q16 is amplifying the current amplified by Q15. This means that Q15 can be used to introduce error feedback. The Blue section contains a voltage divider that scales the output voltage so that it can be used by the bandgap circuit. This bandgap circuit is found in the yellow section (Q1 and Q6). This bandgap reference produces an error signal that is fed into Q7 (orange). A bandgap is used because it can provide a stable output even when the temperature of the device changes.

The orange section takes this error and amplifies it through Q15 and the darlington configuration described earlier. The purple section has overheating protection (Q13) and excessive output current protection (Q14). Occasionally on these schematics you also find excessive input voltage protection marked as Q19 in this section. These shutdown the regulator in fault conditions like overcurrent or getting too hot. The Green section is known as the “start up” circuit, because it provides the initial current needed to power the bandgap circuitry. This gives a jumpstart to the circuit when it needs it.

I chose the LM7805 because 5V is a common value to be used, but the LM78xx series has many different preset voltage versions. The bandgap circuit is trying to get its input to 1.25V, this is from the voltage divider found in the blue section. As R20 is a variable resistor, the voltage divider can be calibrated during manufacture to output exactly 1.25V at any chosen output voltage. This is great for a manufacturer because they make lots of the same chip, and it can be made to suit any voltage output they want. This is also similar to the way some adjustable voltage regulators work, such as the LM317. In adjustable chips, the voltage divider is made by the designer externally, meaning it can be applied to any situation with a simple change of resistors.

Basic Configuration

Looking at the datasheet, there are many applications for the device. but the simplest one is just an input and an output. All that’s needed is a couple of decoupling capacitors to smooth out AC signals and random noise. Voltage regulators work best with clean, smooth power. There is also the need, due to the voltage drop across the transistors, for the input voltage to be at least 2V above the required output. This is always a good rule of thumb to go by when it comes to regulators.

LM78xx basic configuration
LM78xx basic configuration

I would recommend people read the datasheet and have a play with different voltage inputs and current outputs, see how easy it is for it to get hot. In that datasheet there are some other good applications using the device, you can turn it into an adjustable voltage output, constant current supply and high current supply. These are also good projects for learning more about transistors and op amps. Equally, there are other types and brands of regulator out there, some cheap, and some quite expensive, it is worth shopping around for  the ones that suit you.

Luna 1 – The Satellite That Missed the Moon

Luna 1 was the first spacecraft to reach the vicinity of the Moon. Passing just 6000 km away due to an incorrectly timed upper stage, it was meant to impact the moon and spread Soviet pennants to claim the moon as their own. As the satellite ended up in heliocentric orbit, the Soviets renamed it Mechta (Russian for dream), and heralded it as a successful attempt to make a new planet. It was not until years later that Luna 1 was revealed to be a failed plan to impact the mo0n.

A museum replica of luna 1
A museum replica of luna 1

On January 2nd 1959, at 16:41:21 UTC (22.41 local time) Luna 1 was launched from the Scientific-Research Test-Range No. 5 at Tyuratam, Kazakhstan (now named the Baikonur Cosmodrome). Launched aboard Vostok-L 8K72 three-stage launch vehicle, it was the fourth attempt at sending a payload at the moon by the Soviets. The first 3 were:

E-1 No.1 – or Luna 1958A (NASA designation). Launched 23rd September 1958, 07:40. Booster disintegrated 92 seconds into flight due to Excessive vibration. Was the maiden flight of Luna 8K72 Rocket.

E-1 No.2 – or Luna 1958B (NASA designation). Launched 11th October 1958, 21:42. Booster disintegrated 104 seconds into flight due to Excessive vibration.

E-1 No.3 – or Luna 1958C (NASA designation). Launched 4th December 1958, 18:18. 245 seconds into flight, the core stage turboprops lost hydrogen peroxide lubricant, meaning it lost power and impacted downrange.

E-1 No.4 was only a partial failure, and therefore became known as Luna 1. Intended to impact the surface of the moon. Due to an error in timing the upper (third) stage burn time caused a near miss. After 34 hours of flight, at 3.45 UTC on january 4th the probe passed within 5,995km (3,725mi) of the lunar surface, which is about 1 and a half times the moon’s diameter. It was 320,000km from earth, travelling at 2.45km per second. It became the first man-made object to reach the escape velocity of earth. Then after missing the moon it was the first spacecraft to leave geocentric orbit and enter heliocentric orbit.

A replica of the luna 1 attached to the cone
A replica of the luna 1 attached to the cone

The Luna 1 module was hermetically sealed sphere weighing 361.3kg (795.9lb) with 5 antennae extended from one hemisphere; four whip antennas and one rigid antenna. The spacecraft contained a 19.993 MHz system which transmitted signals 50.9s long, a 183.6MHz transmitter for tracking purposes, and a 70.2MHz transmitter. The batteries on board were mercury-oxide and silver-zinc accumulators. Five sets of scientific equipment were externally mounted to the unit to study the journey including a geiger counter, scintillation counter, and micrometeorite detector, along with a Sodium experiment. The device on the end of the center rod protruding out the back is a magnetometer to measure the moon’s magnetic field.

The primary objectives of the mission were to:

  • Measure the temperature and pressure inside the vehicle.
  • Study the gas components of interplanetary matter and corpuscular radiation of the sun.
  • Measure the magnetic fields of the earth and the moon.
  • Study meteoric particles in space.
  • Study the distribution of heavy nuclear nuclei in primary cosmic radiation.
  • Study other properties of cosmic rays.
    Another schematic of Luna 1
A schematic of the Luna 1
A schematic of the Luna 1, unfortunately with russian annotations

at 00:56:20 UTC on january 3rd, 119,500km (74,300mi) from earth, the spacecraft released 1kg (2.2lb) of sodium gas. This formed a cloud behind it to serve as an artificial comet. The glowing orange trail of gas was visible over the ocean with the brightness of a sixth-magnitude star.  Mstislav Gnevyshev at the Mountain Station of the Main Astronomical Observatory of the Academy of Sciences of the USSR near Kislovodsk took a photograph. This was designed as an experiment on the behaviour of gas in outer space, as well as functioning as a navigational aid helping ground control track the mission.

gas cloud of sulphur
Gas cloud photographed by Mstislav Gnevyshev at the Mountain Station of the Main Astronomical Observatory of the Academy of Sciences of the USSR near Kislovodsk

Luna 1 was made of an aluminium-magnesium alloy and sealed with a special rubber. To protect the satellite there was a cone to take the heat when passing through the dense layers of the atmosphere. When safely out of the atmosphere the cone was discarded, and the antennae unfolded. On the same half as the antennas were two proton traps to find the gas components of interplanetary matter, and two piezoelectric pickups to study meteoric particles. The inside of the unit was filled with gas at 1.3 atmospheres, to ensure high pressurisation inside. Through the design, the high pressure allows for an air circulation within the unit. This circulation drew heat off equipment and instruments, transferring it to the shell, that then serves as a radiator.

The nose cone
A replica of the nose cone in an exhibition in 1969
How it fitted
A diagram showing how the nose and luna probe fitted

The Vostok-L 8K72 was a modified R-7 Semyorka intercontinental ballistic missile.The R-7 rocket was designed by Sergei Pavlovich Korolev, known more commonly as the Chief Designer. The 8K72 version consisted of two core stages with four external boosters. The first stage and each of the boosters were powered by a four-nozzle RD-107 rocket engine burning kerosene and liquid oxygen. Total thrust was approximately 1,100,775 pounds (4,896.49 kilonewtons). The second stage used a RD-0105 engine, producing 11,015 pounds of thrust (48.997 kilonewtons). The Luna 1 was propelled by a third stage which remained attached during the translunar coast phase of flight.

Vostok on Takeoff
Vostok on takeoff with the luna 1 on board

After Luna 1 passed the moon and continued on towards heliocentric orbit, it only had a certain amount of battery power left. Because it was meant to collide with the moon it had no need for recharging. On january 5th at approximately 07:00 the radio transmitter ceased to operate at a distance of 600,000km from earth. It is still in an orbit around the sun, somewhere between mars and earth. It completes one rotation in roughly 450 days. for those who understand the terms associated with orbital mechanics here are the numbers:

  • Semi major Axis: 1.146AU
  • Eccentricity: 0.14767
  • Perihelion: 0.9766AU
  • Apohelion: 1.315AU
  • inclination: 0.01 degrees
Luna1 Trajectory
Luna 1 Trajectory

The main aim of the mission was to hit the moon, the reason was to plant 2 Soviet pennants onto the moon. They were highly durable, made from titanium with thermoresistant polysiloxane enamals, that could reportedly survive an impact with venus. Usually a few are minted to give to VIP’s and top scientists. For them, it’s similar to planting a flag. one of the pennants on this flight was a thin metal strip with the inscription “Union of Soviet Socialist Republics” on one side and the coat of arms of the Soviet Union and the inscription “January 1959 January” on the other. The other pennant was spherical, symbolising the moon, each face has the inscription “USSR, January 1959,” on one side and the coat of arms of the Soviet Union and the inscription “USSR” on the other. These pennants were eventually distributed on the moon by Luna 2.

luna 1 pennant 1

Luna 1 pennant 2
The pennants on the Luna 1, that are still inside the satellite to this day.

 

The Foundry: Drilling an Air Hole

At this point we had a cast foundry base, made out of sand and plaster of paris. To see how that was made, see the tutorial here.  Before we first test it though, we had to make one modification, and that was to drill a 30mm diameter hole in the side of it.

The hole from the outside
The hole from the outside

The idea of the hole is to allow air to come in and fuel the fire. The theory goes that the air comes in the side, and the resultant fumes (like smoke) leave via the opening at the top. It makes sense because heat rises, and takes all those hot resultant gasses up with it. Note that we don’t really care about the fumes coming off the fire at this point, we just want as much oxygen as possible to get to the coals. If hot exhaust fumes are leaving via the same hole as the oxygen, but going the opposite direction, they will interact with each other, slow each other down, and make the furnace much more inefficient.

Also notice the hole is angled down into the base of the furnace. This isn’t by accident, we want that hole to do two things, pump air into the base of the fire, and not let anything go back up the hole. This hole in the future may contain a fan, to pump more air in. We don’t want the embers flying back up the pipe and breaking the fan during use.

To drill the hole we used a hammer drill bought from Aldi, and a 30mm masonry drill bit, these parts can be pretty cheap if you search around, and the hole doesn’t have to be this exact size. Use what you can find, and make sure you get help when doing the drilling. As always, safety is important, and safety glasses and gloves would be a good idea. if one person steadies the foundry, while the other drills, it is much easier. Go slow, so that the plaster on the inside doesn’t break too much. It is easy to be too eager and create large cracks and chips, which could mean an entire restart.

The hole from the inside
The hole from the inside, notice the dust, and broken parts around the hole.

Although this was a shorter post, the next one will be about the first tests! As always, thanks for reading, and I hope to be along with another update soon. If you guys have any tips, questions, or want to show your foundry, please post in the comments below.

Why Does NORAD Track Santa?

According to legend, on December 24th 1955, Sears department store placed an advertisement in a Colorado Springs newspaper, where they told children they could call Santa Claus with the number ME 2-6681. Allegedly one digit was misprinted, and calls came through to Colorado Springs, Continental Air Defence (CONAD) Center.

Sears Ad
The Sears Ad that supposedly started it all.

In one version of the story, the calls went through to the “red telephone” hotline that connected CONAD to command authorities at Strategic Air Command. Colonel Harry Shoup, who was a Crew Commander on duty, answered the first call. The story goes that he told his staff to give all children who called later a “current location” of Santa.

Harry Shoup, the Santa Colonel
Harry Shoup, the Santa Colonel

Another description, that is more widely believed is that on November 30th 1955 a child trying to reach Santa on the hotline number in the Sears advert, misdialed and got to Shoup at his desk at CONAD. The response was not particularly kind, and no more calls came to CONAD. Then, when a member of his staff put a picture of Santa Claus on a board tracking an unidentified aircraft that december, Shoup saw an opportunity for public relations.

He asked CONAD’s public relations officer, Col. Barney Oldfield to inform the press that CONAD was tracking Santa’s Sleigh. In the press release, he added that “CONAD, Army, Navy and Marine Air Forces will continue to track and guard Santa and his sleigh from the U.S. against possible attack from those who do not believe in Christmas”. Shoup did not intend to repeat the stunt in 1956, but Oldfield informed him that the Associated press and United Press International were awaiting reports that CONAD was tracking sta again. Shoup agreed, and the annual tradition was born.

In 1958, North America Air Defence Command (NORAD) took over reporting responsibility from CONAD. The reporting became more elaborate, with stories about santa taking rest stops, or one where Santa needed to bandage up one of the reindeer. Eventually, NORAD was renamed the North American Aerospace Defence Command in 1981, and created and published a hotline for the general public to call and get updates on Santa Claus’s progress.

Volunteers answering phone calls in 2007 of NORAD
Volunteers answering phone calls in 2007 of NORAD

Now, Norad relies on volunteers to make the program possible. In 2014, NORAD answered 100,000 phone calls, and in 2015, more than 1200 U.S. and canadian military personnel volunteered to staff the phone lines. From 1997 the program has had a major internet presence with NORADSanta.org. It also has a twitter account of @NORADsanta.