ADC Converter for reading PWM signals

Hi Mayank,

I see Cynthia posted back to you regarding the ADS7853 and I suspect this is part of the same query. What is the output voltage level from your INA240 and what is the minimum pulse width you are trying to capture? Since you are basically trying to read logic 0 or logic 1 (the 'off or on time' of the LED), you probably don't need a 12-bit converter. To your original question, yes, a LPF will round out the corners of your PWM signal and you may not need them for this sort of application.

Hi Tom

The output from INA240A1 can be anywhere between 3V3 to 0V. Moreover, since the PWM is of variable duty cycle, the pulse with can be of duration between 0 milli seconds and 5 milli seconds.

Can you suggest any data converter to read it?

Regards

Mayank

Perhaps I should have phrased the question differently - by "what is the minimum pulse width you are trying to capture?", I'm looking for that 1% value assuming its a valid condition. Your 0 to 5 milli second is 100% off or 100% on. What is the minimum ON (or off) time you need to resolve?

Again - if you need 12 channels, is this for 12 different LEDs in one traffic light? Are they all ON or OFF at the same time? If all you need to do is determine if the LED is on or off, would a GPIO expander work for you? Something like the TCA9535 perhaps?

Hi Tom

The minimum on time for one time period is 0.5 milli seconds.

Yes, there is a separate channel for each traffic light.

A traffic light consists of 216 LEDs and as these become faulty the total current consumption reduces.As a result the amplitude of the PWM output of INA240A1 reduces. That is why I need an ADC, I want to know let's suppose, how much percentage of my the LEDs have become faulty.

Moreover, since it is a PWM @ 200 Hz, any GPIO pin will read it On and Off at the same frequency, hence GPIO will not help in figuring out the percentage of LEDs failure.

I hope there should be some ADC to solve the case?

Regards

Mayank

OK -

Now I am beginning to see the light through the traffic. You are actually trying to measure the current sensed over the INA, which happens to be coming from 216 PWMing LEDs. So if I understand correctly, you have 10 brightness levels and each level represents the current through 216 LED's. Can you look at this as average current draw then for each brightness level?

Hi Tom

Yes, infact the brightness level is user driven on a scale of 1-100.

On each brightness level, the INA240 sense the current and gives proportional voltage output. Now as the input is PWM the output of INA240 is also PWM.

Yes, for each level the current can be average of all the LEDs. I think, this makes it clear.

I hope you may be able to help me now, 

Regards

Mayank