RC Car Help

I am teaching myself and trying to duplicate several projects to control a basic RC car with an Arduino. I have a car disassembled and by connecting a wire from the VCC of the cars board to various pins on the IC can get the car to respond and have mapped Forward, Backward, etc.

I wrote a very basic sketch to output a digital signal from my Arduino Uno but get no response when connecting that output to the cars IC. Clearly I am missing something basic, any help would be appreciated.

CPARKTX:
by connecting a wire from the VCC of the cars board to various pins on the IC can get the car to respond

What voltage is the board's Vcc? It would need to match the Arduino Vcc in order for a direct connection to be safe.

Did you also connect the Arduino ground to the board's ground?

Umm...no (sheepish look). Like I said, I am teaching myself electronics, starting at at very rudimentary level...okay, will try connecting the Arduino ground to the RC car ground. Thanks for helping a noob.

In that case you need to appreciate that what you're proposing to do could very easily destroy the Arduino and/or the car's electronics. That risk can be avoided if you know how to do this safely but it's clear that you don't, yet. Nothing to stop you having a go if you want, but just make sure you're aware of the dangers.

PeterH - Thank your for the caution...I'd rather not all my learning be the expensive type! I used a simple volt meter to check the voltage on the RC board and it appears to be 10v, looking at the specs on this site I believe that is in the tolerances for the Arduino. Any other basic precautions I should be taking?

I think you're reading the allowed power supply voltage range. It's true that the onboard voltage regulator can tolerate up to about 20V. However the digital I/O pins are far less tolerant. The Arduino is liable to be destroyed if you connect anything less than 0V or greater than 5V (relative to Arduino ground) to an I/O pin, and the I/O pin could be damaged if you connect anything to it that draws more than about 20mA. Unless you know what you're doing, it would be very easy for you to destroy either the car or the Arduino, and it would only take a momentary mistake to do it.

So what is the correct approach? Do I add a resistor, and if so what type?

You may want to look into using an optoisolator connected from the Vcc of the RC Car to the input pin of its IC. you can then toggle the opto using the pin out of the arduino. This is of course presuming you can safely inject voltage onto the IC pin of the RC Car without damaging it. in theory so long as you are only bypasssing the cars switch so to speak, that should be fine.

The first step is to ID the chips being used in both the TX and RX this will lead you to the datasheets which will tell you the correct pin to apply your signal to and the format of that signal. Always ensure that the Arduino ground and the ground (battery -ve) are connected.

Mark

CPARKTX:
So what is the correct approach?

Learn enough electrics and electronics to safely hack into an electronic device and interface it to something it was not designed to interface with. There is no silver bullet here, and short of somebody basically doing the research for you and telling you step by step which wire to connect where I don't see any sensible way for you to do this safely.

Do you actually need to use the existing controller? In some ways it would be simpler if you could chuck that out and replace it with an Arduino and motor driver - but some of these really basic RC cars also have steering functions integrated into the controller circuit, and I can't see from here how the steering works.