Connecting PIC to servos

Printable View

- 2nd February 2015, 20:16
The Master

Connecting PIC to servos

Hi, I'm working on a circuit where I need to connect about 15 servos to a PIC chip on separate pins. Each servo will have a wire about 1m long.

In a previous thread I started about interference someone said "connecting long flying wires directly to the inputs of the PIC usually isn't the best design practice". I want to know if the same also applies to outputs.

Should I have something (optos/transistors etc) between my PIC and the servos?

Also, how many volts do servos need on the signal line? I'm using digital servos that need a supply voltage from 5 to 7.5V. My PICs run on 3.3V which should be more than enough for the servo signals but I haven't seen anything to confirm this.
- 3rd February 2015, 02:54
Archangel

Re: Connecting PIC to servos

Hello Master,
I am not sure how this thread merits OFF TOPIC status, but OK.

Kudos to ACETRONICS2 for this link http://www.societyofrobots.com/actuators_servos.shtml

he posted it in this thread http://www.picbasic.co.uk/forum/showthread.php?t=19575

It pretty much explains hobby servos. HTH
- 3rd February 2015, 11:11
Sherbrook

Re: Connecting PIC to servos

My fellow R/C modelling friend has several large models on which the leads to the aileron servos must be at least 3ft long. It all works perfectly.
Phil
- 3rd February 2015, 21:54
The Master

Re: Connecting PIC to servos

Thanks guys, looks like my design will be fine. It's good to know that the same length of wire works in other projects and that link mentions "booster extensions" which I could buy if I do run into problems.

Archangel: I used Off Topic because I didn't think this thread fit into any of the other forums.
- 3rd February 2015, 22:20
mark_s

Re: Connecting PIC to servos

Check this controller. It can control 16 servos. It uses a I2C led pwm chip. You could probably build your own with a little research

http://www.adafruit.com/products/1411
- 3rd February 2015, 22:27
The Master

Re: Connecting PIC to servos

Thanks but I am already building my own. The servo control is part of a larger board that will be responsible for controlling 15 servos, 25 solenoid valves, 2 audio outputs and several inputs.
- 4th February 2015, 01:56
Archangel

Re: Connecting PIC to servos

Quote:

Originally Posted by The Master

Archangel: I used Off Topic because I didn't think this thread fit into any of the other forums.

I was not an "issue", these questions usually crop up in other areas like PBP or PBP3 . . . , throw in some code and it could move to one of those areas as seems pertinent. The questions you asked are valid, esp. since you didn't really know the answer, if you needed to know this, others did too.

The long answer to your question is it depends upon how strong the "noise" signal is vs the signal voltage. If that wire length is able to receive over about 1 volt or so out of "the aether" it could be a problem, worse if it receives 2 volts. Twist the wires and it works better too, less noise received than straight parallel wires.