Fitracer computer control mod

[rmglb]

I've got a 'Fitracer' (quite similar to the Bit Char-G afaik) for quite some time now. And started hooking the controller up to the parallel port of my computer.

The controller works by grounding leads to the chip when pressing a (direction) button.
I hooked it up (ugly) by soldering wires directly onto the PCB, to the buttons/chip. When inactive i set all bits high, so they are at 5volt (from computer, which is higher than the normal 2AA +/- 3Volt). And when active its' grounded. (Ground of parallel port is connected to controller ground).

It used to work qutie well until i soldered things. Sometimes I can drive the car all directions, but often only in afew directions (most of the times i have to steer to let it drive).
I also didn't want to use batteries anymore, but take power from my pc. I'm using the 5Volt line of a PS@ (mouse) connector. I read an article of someone making a plane based on a miniRC and he wrote that the chip should work on 5V or less. He used a 9V block himself so added some more components to get this voltage down.
Here my charge led starts to light up when i simulate buttonpresses, and it doesn't stop anymore. So I'm probably doing something wrong here ;P

*** The controller can work on 5Volt right?

Also charging now isn't that wise.. a transitor and resistor (in the controller) are getting very hot (even at start) and the charge led won't go off anymore. I think the car used to take a current of 0.5A from the batteries when charging. But it's about 1A now when using 5Volt from the computer.
I always thought the controller had some elctronics to measure how much the battery in the car was charged. Since measuring the voltage on the 2 charging leads showed a rising voltage till 2V and then it would stop. But now i understand that that's probably when a capacitor is full, or something.

I'd like to charge the car based on the 5V power supply, but i have to find out how to do this. My car isn't modded and has a normal 1.2V 60MA battery.
*** Any tips on how to do this?

Also i can control my car remotely using a Java Applet (grabbing keypresses) and a webcam stream. But for this i will have to make a docking station where i can charge my car. I've got some ideas for that. But what's the problem is that I can't keep running the car until the battery is empty, since then I can't drive it back to the docking station anymore.
So I'll probably overload the battery eventually, or not?

*** Any ideas about this?

Thansk for your hints/ideas/tips.

[SuperFly]

That's a great voltage to charge a dual cell...

That would be the easiest solution.

[rmglb]

Originally posted by SuperFly
That's a great voltage to charge a dual cell...

That would be the easiest solution.

Well these 2 components on the controller are getting quite hot (resistor and transistor). This might stay like this then too.

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I should try to simply power the remote control with 5V and not connect it to my pc in other ways. Perhaps the problem of the lighting up charge led will go away. That would mean i'm doing something wrong somewhere else..

And i guess i should just guestimate after what period the car should be charged again (counting the driving time). And then just charge it for some time (close to normal loading)..

I should actually be looking for a different miniRC. I saw a stepping-speed-mod somewhere, which i could use very well. Since normal speed is way too fast to control the car remotely driving circles on my table (which i sthe onyl flat surface i have here).

[rmglb]

More:
I soldered 2 wires to a PS2-USB convertor, for a 5Volt and ground line.
When I use thsi as power supply then the charging led doesn't light up when driving the car with the computer.
Ifi disconnect thsi ground line though then it does light up. Even though with a multimeter these 2 lines 'beep' ie connect trough the pc..
Perhaps the ground line trough the lpt connector can't take that much current. I'll see, since this 5Volt line and ground will be connected to the LPT connector, so all is goingtrough one wire.

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Remains the charging problem. I'd prefer to create a 1.2V line from the 5V power line.
SuperFly you say 5Volt is good to charge 2 1.2Volt batteries. But the Battery Basics 101 thread says charging voltage should be as clsoe to the battery votlage sa possible. Here it's still twice as high.
I'm not very schooled in electronics, so the only things i can think of are:
- using a transformer (using coils)
- using resistors, but for this knowing the resistance of the car battery while loading should be know ( i don't know whether there's difference while it's charging or in use).
- voltage regulator as on: http://members.aol.com/rchelicam/microszr/microszr.htm
There it's used to get to 5ish Volt isntead of 9Volt to not burn the controller.

*** So any ideas on this?
I'd also like to get a signal (line that can be 'read' by the LPT port) when the car is charging. Ie i'll have this setup:

PC +5Volt *  |------|
             |      |  * Battery +
PC ground *  |  ??  |
             |      |  * Battery -
PC signal *  |------|