AVR-Chat

Hello folks,

I have an issue that is perplexing me.

I am trying to drive a servo with a Mega 8.

I have a good solid 5 volt supply to VCC.

I am using PORTC as the PPM pins.

If I set portc.3 high (not pulsing), I see it go to 5 volts on my scope.

But as soon as I connect a load the voltage output of that pin seems to drop to 1.8 - 2.5 volts.

I have tried connecting the PPM input of the servo motor (which is just logic level stuff, right?) and a 560 ohm resistor.

I checked the docs, and the Mega8 is supposed to be able to supply 40mA out via an IO pin. Nothing else is connected on any other output pins (except the rs232 pins).

Can anyone offer any suggestions as to why this might be?

Kind Regards,
Stuart Whelan
Technical Director
Pacific Simulators LTD

DDI:      +64  3 3778866
Mobile:   +64 27 2828074

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Stuart Whelan wrote:
> Hello folks,
> 
> I have an issue that is perplexing me.
> 
> I am trying to drive a servo with a Mega 8.
> 
> I have a good solid 5 volt supply to VCC.
> 
> I am using PORTC as the PPM pins.
> 
> If I set portc.3 high (not pulsing), I see it go to 5 volts on my scope.
> 
> But as soon as I connect a load the voltage output of that pin seems to drop to 1.8 - 2.5 volts.
> 
> I have tried connecting the PPM input of the servo motor (which is just logic level stuff, right?) and a 560 ohm resistor.
> 
> I checked the docs, and the Mega8 is supposed to be able to supply 40mA out via an IO pin. Nothing else is connected on any other output pins (except the rs232 pins).
> 
> Can anyone offer any suggestions as to why this might be?

Sounds to me like you have the port set as an input and have the 
internal pullups enabled ;)

Regards,
Kat.