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

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:

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

E-1 No.1 – or Luna 1958A by NASA. Launched 23 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 by NASA. Launched 11 October 1958, 21:42. Booster disintegrated 104 seconds into flight due to Excessive vibration.

E-1 No.3 – or Luna 1958C by NASA. Launched 4 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, 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 unfold. On the same half as the antennas were two proton traps to find the gas components of interplanetary matter, and two piezoelectric pickups for the study of 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

Part of the plan was to hit the moon, unfortunately it didn’t achieve that. Part of 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.

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.