control rc servo with fb

**jm44807** · 01-25-2012, 10:32 AM

hi im a newbie and im trying to control a standard servo with fb. im not having any luck i have read in post where this is doable but no explanation how to hook it up. the servo has 3 wires but fb out only has 2. i tried hooking servo + and - to 5v then servo yellow to fb out + then fb - to 5v ground thats hooked to servo. but nothing happens. will this hook up work is there something in software i need to change ie remap output. im using visual basic i have input /outputs working for other things like activatig relay and reading sensors.

thanks for any help

**2k1Toaster** · 01-26-2012, 01:59 AM

It all depends on what sort of servo it is.

+ needs to go to whatever the servo can take. Since you hooked it to 5v, I am guessing it is a 5v servo.
- needs to go to ground if it is a standard servo, again it depends.

So you can get these from the analogue input pins if it is just one servo. But if you do, try to have it powered externally as USB will not like to power a servo...

If the yellow is the servo control that takes a PWM signal and 50% finds middle, and deviations from that turn it left and right, then it is simple. But when you have it hooked up with just power and no input, it should be completely swiveled one direction and if you move it, it moves back. If it doesn't do this, then it is wrong.

Once connected you have to determine what kind of pulse it needs. Probably a square wave from - to + at some frequency and duty cycle. Hook the + pin to the servo feedback pin via a pullup resistor like a 10K, or 2K or something. Again, depends on the servo. Then hook that node into the - side of the digital output. Send the inverse of the pulse you want, and it should work.

**jm44807** · 02-04-2012, 02:37 PM

thanks for response sorry took so long to get back i fried the stepper motor and have not replaced it yet. i did have a question on last sentence when you say "Then hook that node" what do you mean? the end of resistor? also what did you mean by inverse pulse.

thanks

**jm44807** · 02-04-2012, 05:19 PM

btw it was a hitec the new one is parallax from radioshack

**2k1Toaster** · 02-07-2012, 10:39 PM

When you connect Device A to Device B, the connection it makes can be called a node. So if you want to connect Device C to that "node" then A, B, and C all "share" 1 connection.

Inverse of the pulse. So if it you want a 20% duty cycle, send the inverse of that meaning 80% because "on" means pulling the circuit low. So if you want 20% "on time" you want the circuit low 80% of the time, which means the output of the FB needs to be "on" to 80%. It is active low.