standalone servo control

[wijnendael]

Hi experts, I am looking into the possibility of controlling a servo motor from a pic chip, can anybody give me some information/ideas on this. I wish to probably use a rack and pinion on a small hobby servo motor to lift and lower a object automatically when a input signal is received from something like a rfid chip or similar. Also a second output signal that will operate a solonoid or something to lock the lifted object when no input signal is present. In order to do this what will i need to obtain and what is the easiest method. All suggestions would be appreciated so that i can have a go at this.

 

[alec_t]

The PIC chip may not have the oomph to power the motor and/or solenoid directly, so a buffer stage will probably be needed. Since both motor and solenoid have considerable inductance it will be necessary to use back-biassed diodes, or snubber networks, to suppress back-emf spikes. If you will be using positional feedback then the PIC chip will need A/D conversion capability.

 

[wijnendael]

Hi thanks for the reply, i understand where you are coming from with your concerns and have took this into consideration. I can omit the solonoid from the circuit but it would be a nice feature. I suppose what i am really looking for is some ideas on controlling the servo (just a of the shelf modellers servo) via a pic chip. By this a mean is it simple enough to program a pic chip with something that will say just rotate the motor one way and then the other over a fixed distance via a input signal (source of signal to be looked into later). The motor should turn one way on the input signal and then automatically turn the other after a pre-determined time if another input signal says its ok to do so (forgot this input). I can do this using a running program from a pc via serial or parallel, but this defeats my object of making the unit standalone. Maybe somebody knows of of the shelf equipment that operates a servo from a pre-programmed pic chip ?

 

[wijnendael]

Hi again all, after doing some searching on the net i have found the Picaxe site that seems to offer some pre-made boards etc for running servos and dc motors. Has anyone used this equipment as i am looking at buying the starter kit and one of the servo boards for trying to see what i can accomplish with it.

 

[jpanhalt]

Here are some PIC-based servo controllers:

http://www.diy-electronic-projects.com/p150-Simple-Servo-Tester
https://www.electro-tech-online.com/custompdfs/2011/10/servo_controller.pdf
https://www.electro-tech-online.com/custompdfs/2011/10/PWM.pdf

The first one's code is in Assembly so can be easily converted to the chip of your choice. The others are in C. There is no problem providing the signal to a servo from a microcontroller. As for the power, most servos run well on 5V. Use as an average about 100 MA. Some microservos are less; some really big ones are more. Under load all servos take more power. It is not uncommon to have a model servo pull 1A under load.

John

 

[Pommie]

Have a read of this thread.

Mike.

 

[ghostman11]

i have used pommies code, works great! i had no problem running the servo direct from the pic