CCS/TMS320F28379D: ECAP prescaler for 2KHz signal measurement

Kailas Puri

Tool/software: Code Composer Studio

I want to read signal of rotating shaft which gives frequency from 20Hz to 1.73Khz.

I have initialized GPIO 16 pin as eCAP. I am reading signal but in between eCAP is reading noise.

I am using two DCDC conveters in my circuit to supply +/- 12 V. I have feeling that because of high switching frequency in DCDC converter causing noise reading in eCAP.

I have doubt that eCAP frequency is 200MHz and shaft frequency is less than 2KHz.

Shall i use prescaler for eCAP so that it will not read signal frequency above 2KHz.

If this works then how to use eCAP prescaler in program ?

over 6 years ago

0 Frank Ankapong over 6 years ago

TI__Mastermind 28275 points

Hi Kailas,

All the ECAP does is timestamp rising/falling edges. If your noise is big enough to register as a rising or falling edge, then it will be timestamped by the ECAP. Can you provide a scope shot of the signal in question?

0 Kailas Puri over 6 years ago in reply to Frank Ankapong

Intellectual 330 points

Hello Frank,

I have attached speed(in %rpm) vs time(Sec) graph. This is recorded through SCI. You can see in this there are some spikes.

These spikes are causing me trouble in closed loop control. Input signal is not noisy but in eCAP some spikes it is reading.

If i try to see input signal in DSO, there i can not see any noise.

0 Frank Ankapong over 6 years ago in reply to Kailas Puri

TI__Mastermind 28275 points

Hi Kailus,

Thanks for providing the plot. Unfortunately, the plot doesn't help me in identifying what is going on. I need to see a scope shot of the signal going into the ECAP input. Can you provide that?

0 Kailas Puri over 6 years ago in reply to Frank Ankapong

Intellectual 330 points

Thank You Frank,

But now it is difficult to use DSO probes in board.

But i will try to get it.

One question, what high and low level logic is required for eCAP ?

is it TTL ?

0 Frank Ankapong over 6 years ago in reply to Kailas Puri

TI__Mastermind 28275 points

Kailus,

To debug properly, you will need to scope the signal going into the ECAP. There is no reason to believe the ECAP is malfunctioning but rather correctly reacting to the signal on it's input.

We have VIH and VIL specified in the datasheet. This applies to all digital logic unless specified otherwise. With the exception of some special GPIOs, the device will register a logic 1 for a signal above 2.0v and logic 0 for a signal below 0.8v. Please look at the Electrical Characteristics table in the datasheet.

0 Kailas Puri over 6 years ago in reply to Frank Ankapong

Intellectual 330 points

Frank,

Thank you very much for answers.

There was some grounding issue in my circuit which was causing reading noise in eCAP.

Now its working properly.

Kailas

0 Frank Ankapong over 6 years ago in reply to Kailas Puri

TI__Mastermind 28275 points

Hi Kailus,

Glad to hear it's working now! Let us know if you ran into anymore issues.

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CCS/TMS320F28379D: ECAP prescaler for 2KHz signal measurement