I have had my Arduino Duemilanove for a bit over a year. I got a robo kit, put it togther, ran it for a few days, then tore it apart. I have been through most of the tutorials and have been absolutely ITCHING to build something that has a real use.
I am a software developer (albeit a little green), and I do not have any problems writing the programs that I am interested in. I have a strong grounding in digital logic. Analog circuts are a far different beast. It is a very different way of thinking and the math can get pretty complex (to someone who is new) for a seemingly simple circut.
So for my practical application. I have been getting back into model rocketry with my friends and their kids. My Estes ignition system finally bit the dust. I could probably repair it if I took the time to do it, but what fun would that be? I want to build a replacement that would be based on the arduino and I am having a little bit of a problem trying to figure out the circut.
I was figuring on using a relay that is turned on by a transister. I saw a diagram on this website (will post link below) - that shows how to hook up a transistor to the arduino to switch the relay on/off. It seems like a pretty straightforward thing. A 5v output going to a 2n222 NPN Transistor. That will switch the relay “on” and the relay will do what it does. I want to try to mimic the estes ignition system as close as possible.
With 4 AA rechargeable NiMH batteries in series, the launcher outputs 20mA to the igniter when the button is not pressed. It uses a lightbulb to restrict the current, and light up for a continuity check (this is not enough to light the igniter). When you press the button down, it bypasses the lightbulb and sends 5A to the igniter, setting it off.
For now, I am only interested in the base case of building a circut that will output the 5A on the relay, I will do the 20mA part of the circut later. I want to use a SPDT relay, default (relay “off”) will be the 20mA part of the circut. When the relay is on, it should be capable of sending the full 5A for a brief period of time, maybe .5s just to be sure
Here is where I am lost.
My current list of parts:
2n2222 NPN Transistor
5VRelay that can handle 5A I was thinking these might work?
1n4004 diode (Link Below)
resistors, specifically a 1Kohm in my current circut
a 4AA battery pack to power the relay and the 5A firing part of the circut
I am using a piece of software to simulate the circut before I purchase all of the stuff to build the circut (frugal I know). It is called CircutMaker and it is telling me different results than that I am expecting. IT is possible that the app is wrong, or that I am wrong, but something does not seem to add up. He is my attempt at the circut, borrowed mostly from the pdf mentioned above.
I have a “multimeter” reading the amps on that circut, and it is telling me about 5kA? That is probably not correct. Maybe that application is adding unneeded complexity. the 5V on the left is the arduino, the 5v on the top is the battery pack.
Does anyone here have any input on what I am doing wrong, or how I could do this better? I am open to any suggestion.
Thanks in Advance,
PS: Before you warn me of the dangers of playing with fire, I am well equipped and qualified to handle the materials =) I am quite careful.