long wires on digital signal

[Rajinder]

Hi,
I am driving a PWM circuit and low pass filter from a microcontroller. The output from this circuit will have a voltage in the range of 5-15mV.
However there is a cable (twisted pair with overall screen) between the microcontroller and this PWM circuitry. The cable is around 12-18 inches length.
I'm concerned about noise pick up as I only have a few mV that I am using.
Any help would be appreciated.
Thanks

 

[Harald Kapp]

There are a few possibilities:

1. Put the low pass filter at the end of the cable. That way the filter will suppress noise that's been picked up, too.
2. Make the PWM signal generate not 5 mV ... 150 mV but e.g. 150 mV ... 4500 mV (a factor of 30). put an attenuator 1/30 at the and of the cable to get 5 mV ... 150 mV from the higher voltage input. This will attenuate any noise, too.
3. Combine both methods: generate a PWM suitable for 150 mV ... 4500 mV as input to the cable. place the low pass filter + attenuator 1/30 at the end of the cable to filter and attenuate any noise.
4. In addition: use shielded cable, shield connected to ground, to minimize pick-up of noise as your first line of defense.

Harald

 

[Rajinder]

Thanks Harald.
What would be the best way to attenuate, a potential divider?

 

[Harald Kapp]

That's what I was thinking of.

 

[Rajinder]

Thanks