How to prototype a PCB #2?

Question

Dear: Element 14

Hello I have made many changes to my Rocket Controller since you last saw me. First of all I added voltage regulators to my PCB to make my PCB be able to amplify the current to 9 volts to detonate the ignition. Also I have made my PCB easier to read and removed a lot of diodes because that was unnecessary to have that many diodes in there. So does this new PCB look right to you?

From: Noah

shabaz · Accepted Answer

Hi!

You're correct, this is an okay circuit to get a higher voltage to a fixed 5V output. I think he used it to drive his Atmel chip. However the part of the circuit which is used to ignite the fuse only uses this 5V supply to drive the transistor which turns on the relay. The voltage which launches the rocket (through the relay contacts) is not the 5V supply from the regulator, but rather a higher voltage from a battery (either the same or a different battery - a different battery is definitely preferable).

The relay circuit is a bit over-the-top too to be honest, but will work.

If you want a purely silicon way to do this, I can try to find you a circuit - but you'll have to test it out, no guarantee it will work.

shabaz · Answer

Hi Noah,

Unfortunately this is not what voltage regulators are for; they won't effectively launch your rockets. The reason you're maybe partly having trouble is that you might be searching for the wrong thing. If you search for 'launch controller' (which is the correct term) you'll find lots of useful information. Also, it's advised to test one channel on breadboard before laying out your PCB. Otherwise you'll have to redo your PCB, and that's wasted effort. Also, a good reason of the off-the-shelf Arduino board and a breadboard (the white plastic prototyping boards) is that they make it easy for you to prototype and test something before you create a PCB for it. Without doing this, it is like running before walking.

The website here contains some example circuits. You can see that he used a transistor and relay, and so this is a tried-and-tested solution that you could choose if you liked or perhaps make some modifications/improvements to it. On the next few pages the author walks through the entire circuit including microcontroller and the code too, and the PCB design. You can see his PCB has far thicker traces in places than your board. By reading his information and looking at the design, you can then begin to plan how your design and your PCB will look like.

shabaz · Answer

Hi Noah,

I had some time to try out a quick non-relay circuit.

I just used whatever components I had, and I've not done any calculations, so I'm not guaranteeing this circuit to work reliably always. However, I did test it since I had a little motor and a fuse spare. It was ignited outside the garage but the smell went everywhere : )

This was the circuit:

And this was the result afterwards:

For the battery (BATT_LAUNCH in the circuit), I used 4xAA, i.e. 6V.

For the microcontroller input, I didn't use a microcontroller. I just connected to a separate 3V supply to simulate that (I used 2xAA batteries for that).

The fat wires in the circuit diagram need to be fat traces on the PCB.

For safety, you should of course have a switch that disconnects BATT_LAUNCH until you're ready.

With the circuit as described, you should be able to connect it to any Arduino board and use it (but don't power the Arduino from BATT_LAUNCH, use a

separate supply).

Please use an existing Arduino schematic and modify slightly if required, there is no point re-inventing the wheel. This way you're almost guaranteed to have

a successful project.

How to prototype a PCB #2?

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