Driving Servos

[fritz42_male]

Sorry if I am being dumb but can anyone tell me why all the picaxe examples drive servo signals via a 330 ohm resistor and can it be omitted?

The reason I ask is I have seen other PIC hobbyists driving directly off the chip output.

I've knocked up a simple 3/4 servo controller based on the 08M proto board which works well. However, I had to bypass the 330 ohm resistor to get a triac to fire on the delay/duration timer I used it on. If I can omit the resistors from the design completely, it would simplify the board even further.

Cheers

Mike

 

[inglewoodpete]

Sorry if I am being dumb but can anyone tell me why all the picaxe examples drive servo signals via a 330 ohm resistor and can it be omitted?

The reason I ask is I have seen other PIC hobbyists driving directly off the chip output.

I've knocked up a simple 3/4 servo controller based on the 08M proto board which works well. However, I had to bypass the 330 ohm resistor to get a triac to fire on the delay/duration timer I used it on. If I can omit the resistors from the design completely, it would simplify the board even further.

Cheers

Mike

You can probably guess what the resistor is there for: as a current limiter. Yes, you can probably get away without the resistor. I haven't had extensive experience with servos: possibly the signal lead in the servo can go short circuit to + or 0v and overload the PICAXE pin. Alternatively, if you run the servo of 6v and PICAXE off 5v, there could be additional current passing. However, I'm guessing.

 

[Technical]

It's an extra protection thing, if you never make mistakes and never wire things up incorrectly then do don't need it.... if you do sometimes make mistakes its a cheap way to help protect the PICAXE!

 

[fritz42_male]

Thanks guys. That's what I assumed but wanted to check. I'll play around with values to see if I can get the SSR to fire with a resistor in place and then test with servos as well.

Cheers

Mike