Converting RC car to computer controlled car
Golgathus
currently trying to learn. I have an old RC car that I want to control
via my parallel port. After several nites of research I know how the
port works and have seen examples of converting models that are simple
all or nothings (100% speed forward/ back). But my remote uses a pot
on each of the remote's sticks. My idea is to use the 8 data pins on
the parallel port to control both the speed and directional controls at
the same time. The first 4 would be for speed, and the 2nd four for
direction. to replace the pot (analog) with the digital parallel port I
decide give up on a true DAC, instead I think a step system would be
better. the first byte (pin) would set forward/back (left/right) and
the remaining three would set speed (angle).
For instance:
Pin 2 = 20% of power into Pot.
pin 3 = 30% of power into Pot.
pin 4 = 50% of power into Pot.
In this method i would be able to combine the pins to reach 100% and
still have some of the controle that the original analog system had.
(ranges of 0,20,30,50,70,80,100)
So here are my questions/problems at last:
Is this a sound plan? Is there a better way?
Kevin Gomez
1. Use parallel port to generate the signal which modulates your RF
carrier. Need to probe around in your transmitter (Tx) with a scope if your
Tx does not have a buddy port (look for signals like in links below).
2. do '1' except use a simple microcontroller (e.g. 8-pin PIC) in between
parallel port (or COM port..) and Tx to un-burden PC.
somewhat like http://www.mh.ttu.ee/risto/rc/electronics/pctorc.htm
http://www.rc-electronics.co.uk/PCBuddyProgManV1.pdf
3. If the goal is to learn more electronics, then one other option which
should also work with non-standard Txs too is to use a digital
potentiometer - wide range here;
http://www.digikey.com/scripts/dksearch/dksus.dll?Criteria?Ref=3320&Site=US&Cat=32375472
one example;
http://rocky.digikey.com/WebLib/Analog%20Devices/Web%20Data/AD5162.pdf
Have fun,
Kevin
"Golgathus" <mtdew...@hotmail.com> wrote in message
news:1127628429....@g43g2000cwa.googlegroups.com...
eck...@gmail.com
4-bit adcs. That way with n pins you get 2^n options (16) instead of n
options as you suggest. First, though, you should make sure that the
transmitter uses the stick pots as variable voltage sources. If it
uses them in some other way, such as part of a variable frequency
oscillator as many computer gameports do, this won't work.
The digital pot option, as previously mentioned, would also be pretty
easy to implement.
chris
Golgathus
microcontroller? Don't think I'm ready for that yet.
Kevin Gomez
emulated on a couple of lines of the parallel port (one for data, one for
clock etc).
"Golgathus" <mtdew...@hotmail.com> wrote in message
news:1127877074....@g44g2000cwa.googlegroups.com...
Mike Young
> currently trying to learn. I have an old RC car that I want to control
> via my parallel port. After several nites of research I know how the
> port works and have seen examples of converting models that are simple
> So here are my questions/problems at last:
> Is this a sound plan? Is there a better way?
You need to emulate the receiver, not the transmitter as suggested
elsewhere. Skip past all that, and research what the servo needs to see for
control. The servo expects a timed pulse as its control signal, roughly 30
times a second. A high pulse of a certain duration means to hold center. A
shorter pulse means to move in one direction; a longer pulse means the other
direction. You'll find the specifics in a web search.
This means you can control up to eight channels without multiplexing 8
digital output lines. (How?) There's no messy digital-to-analog conversion.
Golgathus
car's remote to my computer, not rebuild the car. I only need to
replace the physical act of moving a joystick with a signal from my PC.
Jon Sutton
The pot in your remote will provide a voltage somewhere between 0v and
the supply voltage depending upon the position of the stick. The
electronics use this voltage to set the transmitter output such that the
center position (1/2 supply voltage) gives the neutral (stopped or
center steering) signal. As you move the stick forward the voltage
increases (or decreases depending on the make of your transmitter) and
the transmitter sends a corresponding signal. Commonly 0 volts will
correspond to full speed reverse and supply = Full forward.
I'm supposing you realise how the POT works...
From what you describe you would probably manage with 2 x 4 bit DACs,
giving you 16 voltage levels for each channel from your 8 bit port.
Which is pretty much a 'Step system' anyway.
The only issue would be getting your center position to provide the
correct voltage for 'neutral'.
The voltages might not be 0V and supply - you would need to check this
with a meter or scope and then arrange for your DAC to provide the same
voltage range. Perhaps using an OPAmp to provide buffering and a little
voltage offset.
Hope this helps.
Jon.
Si Ballenger
<mtdew...@hotmail.com> wrote:
So what have you tried so far or experimented with in your setup?
I'd think you would make a resistor bank that you would put in
parallel with the joystick pot. These resistors would be put
in/out of service via NPN transistors controlled via the parallel
port pins. You probably can get the components from the local
Radio Shack. If they have the 74HCT259 chips (276-2868, $1.49) in
stock you can use it to have more resistors available. The below
links are for controlling a homemade webcam video switcher, but
should apply for controlling resistors via the parallel port.
http://www.geocities.com/zoomkat/ppswitcher.htm
http://www.geocities.com/zoomkat/ppswitcher3.htm
Golgathus
using npn and pnp transistors. Since the remote uses both outs from
the pot, I set up a chain of risitors that act as the resistance before
the sweeper and after the sweeper to sum to 4.8K Ohm (original value of
pot). I haven't finished building the circuit yet so don't know how
well it will work yet.
Thanks for the link.
Golgathus
newtype
news:1130088825.8...@g14g2000cwa.googlegroups.com:
Have you tried to use an electronic simulator?
Are you using 2n3904 and 3906 ?
thanks
Golgathus
to use two 4 to 16 decoders.. Decided on the 74154 So now the
transistor relay (60 total transistors) wil be replaced with two 24 pin
chips. Much cleaner design and less soildering. Logic remains the
same. Just waiting for parts to arrive.