Comments on: Simple serial servo controller

By: Stevo

Stevo — Fri, 04 Mar 2011 18:05:51 +0000

The 100 ohm resistor is ACTUALLY a good idea. They shape the pwm rising edge to prevent broadband noise on every rising and falling edge. Ever looked at the frequency spectrum of a pulse? Not pretty. It’s also a good idea to have because the servo can fail with a dead short to gnd which would pull more current through that little PIC pin damaging it. The Resistor limits the current in this situation saving the PIC.

By: Bullwinkle Jones

Bullwinkle Jones — Sun, 27 Apr 2008 08:39:53 +0000

I must apologize for last nights obviously drunken writings.. Bad Matthew!

By: kwa

kwa — Sun, 27 Apr 2008 03:04:15 +0000

Hackius, the “c” is the non-flash version. You can only burn the code into the chip once, they are just a bit cheaper than the flash rewritable ones.

By: mike

mike — Sun, 27 Apr 2008 01:59:27 +0000

It is nice having such a low parts count, it really makes stuff compact and easy to build. But you just can’t beat the dedicated servo controller chip…especially if you don’t know how to program pics like me. I know all the syntax for java and perl and stuff, I just don’t have the creativity to make good programs, so having a dedicated part to do a job is still a high priority in my book.

By: N0QBH

N0QBH — Sat, 26 Apr 2008 22:24:34 +0000

Here's a couple of my own simple PIC 12F675 servo controllers.
http://www.ringolake.com/pic_proj/servo/servo_weasel/servo_weasel.html

By: andrew

andrew — Sat, 26 Apr 2008 22:10:02 +0000

hackius: the c means that the micro can only be programmed once. since f and c types are interchangeable, the c types aren’t used much anymore except in mass production.

By: Hackius

Hackius — Sat, 26 Apr 2008 20:30:10 +0000

12C?

What does the C stand for? I know the F family of microcontrollers is named after the internal flash but I've never heard of C family.

By: brandon

brandon — Sat, 26 Apr 2008 16:41:53 +0000

I’ve built many serial servo controllers and you don’t need those resistors. All that is required is a PWM output to the control line of the servo. Thats a part count of two: servo and mcu.

By: Almost There

Almost There — Sat, 26 Apr 2008 16:32:43 +0000

I agree, the resistor between the PIC and the Servo is not required. Most Micro Controller manuals are geared toward the beginner, and have the resistor to protect the Micro against a miswire (accidentally hardwired to a power supply rail.)

It should be trivial to write a timed routine in any modern language (C#, Java...) to toggle a pin on the Serial or Parallel port every 20mS. It may have some jitter, but it also has a zero parts count!

By: julian

julian — Sat, 26 Apr 2008 12:52:11 +0000

crash, just use some atmega8, a transistor as motor driver and some usb->rs232 chip.

By: Crash

Crash — Sat, 26 Apr 2008 11:44:54 +0000

Does anyone know how to simply control a small 3-5v DC motor through USB? I would like to see that.

By: spaceballs

spaceballs — Sat, 26 Apr 2008 09:19:26 +0000

why need the resistor from the pic to servo, look at http://www.epanorama.net/documents/motor/rcservos.html it seems servos take an 5v input control wire.

By: Bullwinkle Jones

Bullwinkle Jones — Sat, 26 Apr 2008 08:15:05 +0000

“There’s nothing quite like a nice, simple hack. This serial servo controller uses a PIC12C671 and a pair of resistors. Leaving out the power supply, that’s the lowest part count I’ve ever seen.”

..”_this_ servo controller”.. The “_this_” syndrome is almost as bad as the click _here_ syndrome.. Perhaps “This _servo_ _controller_ ..” would be better.. I think I’m just taking the piss though, and also I’ve had too many beers.. I’ll shut up now.