Hacking a RC car and controlling it with computer

I hope you got much concept about parallel port interfacing. Now lets get more complex.
What do you think about controlling a Vehicle using your keyboard? or mouse?
Today I am going to teach you step by step procedure to control a RC car using parallel port.
Things you’ll need:

RC car(Better if you buy Multi functional car)
Circuit Board (Blank circuit board)-optional
NPN transistor : BC547 or BC548 or BC546 any of these. (4)
Parallel port male connector
Few resistor about 500 ohm or similar to that.

Now lets begin with the project.
To get the job done, you’ll need to modify the Transmitter(Remote Control) of the RC car.
Unscrew all the wires of the Remote control. And memorize or mark the Positive and Negative terminal of the circuit and write down which wire goes where in the piece of paper. Now you can break the wires as you’ve noted down all the connections.
If your car is direction controllable then you’ll have four buttons in the Remote control circuit. In a single button, two metals comes in contact and guide the car to move or turn.
What we are concerned with, is the positive “side” of the switch. For each switch, you need to identify which side is negative and which is positive(mostly the common point of contacts are negative, check the continuty or discountinuty of the negative terminal by pointing multimeter either of the point of contact of button with the negative terminal of the battery). Solder a wire onto each positive side and one wire to a negative terminal (there are many negative terminals on the PCB, it doesn’t matter which you choose because it is common terminal). You should have 1 wire per switch soldered, and one wire to the negative terminal.

Here is what I did.

Green wires are connected to the switch and black is already connected with negative terminal of the battery, you can soldier another wire with the negative terminal of the battery case as well.
Red wire goes to positive terminal of the battery…..
Now you are 80 percent done in the transmitter circuit.

You’ll have to make an interface such that computer will communicate with the remote control PCB.
For this you’ll have to read my earlier post about parallel port
If you haven’t read read the above linked post then read it and come back here again.

Ok now you are back. Hope you got little bit concept on parallel port.
I told you to buy the male connector of the parallel port with 25 pins did you buy it? Well if you did then its OK now here is what to do next.

Take the male parallel port connector and solder short wires to pins 2,3,4,5,18. Pins 2-4 will carry the data (forward, reverse, left, right and it is Positive terminal of Parallel port) and pin 18 is ground(Negative terminal from the parallel port). Side note: when doing any pc-parallel port interfacing, pins 2-9 are easily controlled data pins and pins 18-25 are all ground. Other pins have specialty functions and can be used in interesting ways for example inputing.

When completed, it should look similar to the picture above.

The rest consists on building a circuit, using the schematic (diagram) I have made up. For this you need, a bunch of small wires, solder board, four NPN Transistors(refer to materials required at the beginning of the post). Build the circuit from the schematic diagram given below. Note that, the ground is the Parallel Port Pin 18 and Remote Negative Terminal connected together, there is no ‘third’ ground .
Refer to the circuit below.

Here is a picture of the whole complete circuit (I haven’t kept any resistor for a while)
If you are confused which leg of transistor to join parallel port and which to the ground. Then Hold the transistor with flat part facing towards you.
The Left leg goes to the ground and right one to the wire that you’ve soldered in the Remote control PCB.

Now the hardware part is done in next post I’ll post about software part. Stay tuned.

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