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Posted by Golgathus on September 25, 2005, 2:07 am
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Let me start by saying I am not very good with electronics (yet). I am
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?
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Posted by Kevin Gomez on September 25, 2005, 2:39 pm
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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
So here are my questions/problems at last:
> Is this a sound plan? Is there a better way?
>
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Posted by eckern@gmail.com on September 25, 2005, 9:19 pm
Please log in for more thread options It would give you more possible speeds if you set it up as a pair of
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
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Posted by Golgathus on September 27, 2005, 11:11 pm
Please log in for more thread options I was trying to avoid the digital pot, I thought that they require a
microcontroller? Don't think I'm ready for that yet.
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Posted by Kevin Gomez on September 28, 2005, 1:19 am
Please log in for more thread options Most digital pots use a serial interface (eg. SPI) which can be readily
emulated on a couple of lines of the parallel port (one for data, one for
clock etc).
>I was trying to avoid the digital pot, I thought that they require a
> microcontroller? Don't think I'm ready for that yet.
>
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