Clean Signal Questions

mhamen3

Hi guys,

Do you recommend putting a pull down resistor between the prop and a servo? If so what value?

Also, if I want to use an xbee module with the prop should I put anything between the xbee and the prop to keep the serial signal clean? Or is it ok to just plug it straight into the prop?

Thanks,
Marc

Leon

Servos don't need a pull-down resistor.

Mike Green

There's no need to put anything between a Prop I/O pin and something else to "keep the signal clean".

Sometimes it's helpful to put a 1K or 2.2K resistor between a Prop I/O pin and a servo control input to prevent noise from the servo from getting back into the Propeller

If the "something else" is an output and the Prop pin is an input and the "something else" operates at 5V, you'll need a 2.2K resistor to protect the Prop I/O pin from the possible 5V.

If the "something else" is an output and you might possibly make a mistake in your program so the Prop I/O pin accidentally becomes an output pin too, a 2.2K resistor between the Prop I/O pin and the "something else" will protect both from damage from the potential short circuit.

The xBee operates on 3.3V, so only the last reason applies.

Phil Pilgrim (PhiPi)

Adding to Mike's list, if the "something else" is a MOSFET gate or other high-input-impedance device that you don't want operating when the Prop is in reset, use a pull-up or pull-down to set the default state while the Prop pin that drives it floats.

Also, if the Prop pin is driving a long cable, a pull-up, pull-down, or voltage divider termination at the other end of the cable can help to prevent noise pickup from causing glitchy operation. The same holds true if the Prop is receiving data over a long cable: a pull-up, pull-down, or voltage divider termination at the Prop pin can help to reduce the effects of noise picked up along the way.

-Phil