Digital Sampling of PWM - Electronic Circuits Projects Diagrams Free

2camjohn · 2nd March 2007, 05:03 PM

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** · 2nd March 2007, 05:07 PM

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 · 2nd March 2007, 05:53 PM

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** · 2nd March 2007, 07:06 PM

Quote:

Originally Posted by 2camjohn

Its an IR phototransistor.

It will respond nicely to the PWM frequency

Quote:

Unfortunately Im restricted to software changes only right now.

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

Quote:

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 · 2nd March 2007, 08:13 PM

Quote:

Originally Posted by 2camjohn

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.

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2nd March 2007, 05:03 PM	(permalink)
2camjohn	Digital Sampling of PWM 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 __________________ The first rule of mstechca club is do not talk about mstechca club. http://www.electro-tech-online.com/s...induser&u=1245

2nd March 2007, 05:07 PM	(permalink)
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. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

2nd March 2007, 05:53 PM	(permalink)
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. __________________ The first rule of mstechca club is do not talk about mstechca club. http://www.electro-tech-online.com/s...induser&u=1245 Last edited by 2camjohn; 2nd March 2007 at 06:50 PM.