Picture of Hacking the Spy Video Trakr II
In the previous Instructable, "Hacking the Spy Video Trakr" (http://www.instructables.com/id/Hacking-the-Spy-Video-Trakr/), you learned how to open up the Trakr and install male headers in the GPIO connections on the circuit board. You also learned how to write, compile, and install a short program on the Trakr to flash LEDs by pressing the A and B buttons on the Trakr remote. Of course, getting the Trakr to flash LEDs isn’t very interesting, but now that you’ve completed your first Trakr hack, you can try more sophisticated hacks.

The voltage output directly from the GPIO pins is only 3.3 volts so, there aren’t many devices other than LEDs that you can drive with such low voltage. If you wanted to control, say, a Lego motor that runs on nine volts, you would need a nine volt voltage source yet prevent accidently sending nine volts through the Trakr’s processor and frying it.

When deciding what kind of circuit to connect to the GPIO pins, always apply the maxim, “Keep It Simple, Stupid” (KISS). If, for example, you wanted to drive a single motor in only one direction, the simplest device to keep a higher voltage source–the one used to drive a motor–from accidently passing through the Trakr’s processor is an electronic relay. This Instructable will demonstrate how to use a relay to control an external device with the Spy Video Trakr. You'll learn how an electronic relay works, what the electronic scematic diagram for a relay looks like, and what an actual electronic circuit diagram in which the relay is used looks like. You'll learn how to make conversion cables to connect the Trakr to external devices. You'll learn how to make  a larger cargo deck for the Trakr and see some examples of how some devices can be mounted on the Trakr. You'll learn how to tap into the Trakr's 9 volt and five volt power supplies. Finally you'll learn how to use the electronic relay to control an foam dart missile launcher.
vov353 years ago
Use a MOSFET. get $3, go to radioshack, look in the bin labeled "transistors".

You'll never go back to mechanical switching again.
KRA5H (author)  vov353 years ago
Thanks for the comment. I do use the L7805 in my project: Dance Dance Roverbot! Build a Light Activated Dancing Snap Circuits Programmable Robot.

vov35 KRA5H3 years ago
The 7805 is a voltage regulator, I'm trying to get you to buy some power transistors for switching reasons. :p

MOSFETs have electrically insulated gates so you won't damage your microcontroller, and they will allow you to control a significant amount of electrical power using a very small voltage and almost no current.

I know they look the same as far as plastic package/ three pins goes, but they're completely different solid state devices.

To help you understand, here's a sample circuit from the wikipedia page https://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Mosfet_n-ch_circuit.svg/220px-Mosfet_n-ch_circuit.svg.png
I'll leave you to your own devices for research from there.
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myfcr3 years ago
have you tried using an optocoupler?
freeza363 years ago
Where is the foam in this instructable?
KRA5H (author)  freeza363 years ago
The foam darts taht the missile launcher fires.
freeza36 KRA5H3 years ago
cool instructable by the way
freeza36 KRA5H3 years ago
Oh ok i see now
mikeasaurus3 years ago
Mobile platform for all kinds of awesome!
(Also, you should enter this into the foam challenge!)