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View Full Version : Long distance Parallax servo cables. ( Long distance cable and Basic Stamp )



markuster
02-01-2010, 11:56 PM
Hi,


I need to move two Parallax servos ( one servo is closer than the other one).

The first servo distance is about 35 feet and the distance
for the second servo is more than 100 feet.

I know that energy cables ( +6 and Vss) must be thick ,
but my problem is about the PIN cable , because
the Pin cable brings little signals and this cable could bring
some interference or noise.

How can avoid these problems?

Thanks, Mark

Mike Green
02-02-2010, 01:11 AM
35 feet is marginal, but probably doable by using a separate twisted pair for the signal wire (and ground). You will have problems with noise from the motor conducted back along the power ground. You may be able to help that with filtering at the servo end (using a large capacitor across the power leads - maybe 1000uF to 3300uF).

100 feet will be problematic. An easy solution would be to use a MAX232 at each end or RS485 drivers. With the MAX232, you'll get the benefit of higher voltages over the 100 feet, filtering of noise, and control of signal slopes (rate of change). You'll get the same with RS485 along with differential signalling (probably not needed over just 100 feet unless it's an electrically noisy environment).

allanlane5
02-02-2010, 01:30 AM
Mind you, if you use the MAX232 or RS485 driver approach, you'll have to have a power voltage wire down the cable to power the remote driver chips. Having that 1000uF to 3300 uF capacitor at the remote end will be very necessary.

markuster
02-02-2010, 11:48 PM
Hi, Mike and Allan



I was thinking to use an standard 2N2222 transistor in order
to amplier the signal.

Is the MAX232 a better solution instead the 2N2222 transistor ?

It is important for me to work with long distance cables 100 feet or more
for this reason your opinion is very usefull .

Thanks, Mark

allanlane5
02-03-2010, 01:13 AM
"Amplify" the signal to what?

The BS2 already can put out a zero to +5 volt signal with 20 mA of current behind it. It's the recieving side that has a difficulty with signal loss and noise addition. The nice thing about the MAX232 is that it uses +- 9 volt signalling levels -- it has an on-chip "charge-pump" to generate those voltages. AND it uses the RS-232 standard, which was designed for these kinds of applications.

So yes, a couple of MAX-232 chips would be an excellent, reliable solution to this problem. Where a 2N2222 could be error-prone.

markuster
02-04-2010, 12:10 AM
Thanks ,


My problem is that I need a lot of knowledge of electronics
but tips from you and Mike are usefull .


Any way , do you know where can I find an schematic or explanation about how to add
the MAX232 ?


Thanks, Mark

kf4ixm
02-04-2010, 12:16 AM
here is a link that may help you to make the converters for each end of your run...

http://sodoityourself.com/max232-serial-level-converter/

it uses the max232 chips from maxim.