Digital Sampling of PWM

[2camjohn]

I have a LED whos power i want to control by PWM, 1khz. Duty cycle adjustable from 20% - 50%.

This LED points at a sensor.
This sensor is sampled at a rate of 25khz.


Im struggling to get my head around whether the sensor will consider the LED to be a digital series of pulses, or one analog signal.

Can any of the clever Trevors on this forum offer any advice? Websites to look at or whaterver. Its more important to me that I understand whats going on, than whether I get the correct answer.

Cheers
John

 

[Nigel Goodwin]

What sort of sensor is it?, if it will respond to the PWM pulses then those pulses will appear on it's output. You might consider PWMing MUCH higher (say 100KHz) and lowpass filtering the output of the sensor.

 

[2camjohn]

Hi Nigel,
Thanks for the speedy and sound advice as always.




Its an IR phototransistor.

Unfortunately Im restricted to software changes only right now.




The purpose of the PWM in this situation is to effectively get a lower intensity signal at the reciever, however im starting to think thats a bit of a flawed concept.

 

[Nigel Goodwin]

Its an IR phototransistor.

It will respond nicely to the PWM frequency

Unfortunately Im restricted to software changes only right now.

Does the word 'stuffed' mean anything to you?.

The purpose of the PWM in this situation is to effectively get a lower intensity signal at the reciever, however im starting to think thats a bit of a flawed concept.

Yes, but why would you want to?, is it for range finding?, easiest method though would be to switch different series resistors in circuit.

 

[philba]

The purpose of the PWM in this situation is to effectively get a lower intensity signal at the reciever, however im starting to think thats a bit of a flawed concept.

I don't understand the point of this. are you overloading the receiver or something? Put a neutral filter in front of it if you are.