Buffering MCU output for remote servo control?

CuriousOne

Hello.

I'm building custom wildlife observation camera, which will be controlled using basic stamp and servos (up/down, left/right, zoom in/out, focus in/out). The control panel will be away from camera itself with servos about 30 feet. I want to deliver steady signal to servos, and also protect MCU from short circuit, hot plug, static and so on. This is why I want to buffer control outputs (servos will receive power from separate, stabilized power supply). Currently, I have the following IC in stock, and I want to re-use them, without need for buying something else. These IC's are:

CD4050
74HC04
ULQ2803

Which one will be the best choice?

Mike Green

Actually, none of those would serve as a buffer for a servo signal. The CD4050 and the 74HC04 can only deliver about 5mA. The ULQ2803 is a Darlington array, not a buffer. The Stamps have a pretty good output stage that can deliver 20-30mA. A 1K resistor in series with the output pin would protect the Stamp from short circuits and would dampen noise fed back into the the control lead from the servo motor itself. The I/O pin is already somewhat protected against static electricity and the resistor will help. Do remember that the Stamp's ground has to be connected to the servo power supply's ground.

You might want to use 4 twisted pairs for the 4 servos with a ground for each. That will help keep the control pulses from coupling through to each other over the long cable. You could use CAT5 cable for that and a separate cable for the servo power.

CuriousOne

Yes, I'm going to use STP cable, for better shielding.