Interested in capturing sinusoidal or ramp signals using LPC1549.

[doini]

Hello,
 
I am using the LPC1549 to capture square wave signals using SCT in the capture mode set for rising edge of the input signal. This is working very well.
Now I would like to capture other signals than square wave, for example sinusoidal, ramp, or other signals, so my question is how can I do that. The thing that I am interested in is to determine the frequency of the incoming signal.
I would appreciate any answer.
 
Thank you,
Doini

[kerryzhou]

Hello Doinita Marcu,

       If you just want to get the frequency of the sinusoidal, ramp wave, you still can use the same code as the square wave.

    Still use the rising edge to capture the wave.

     You can try it, any question, just let me know!

  Wish it helps you!

Have a great day,
Kerry

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[doini]

Hi Kerry,

Thank you for your answer.

I have put a sinusoidal signal (and then a ramp) on the Capture input of SCT which I had used for a square wave signal, and I used the same code as for the square wave, with capture on the rising edge, but I cannot capture these signals at all.

Any further help on this would be greatly appreciated.

Thank you,
Doini

[kerryzhou]

Helllo Doinita Marcu,

  Please give me the oscilloscope waveform  of your sinusoidal signal (and then a ramp) , I need to know the amplitude and the frequency.

Waiting for your reply!

Have a great day,
Kerry

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[doini]

Hi Kerry,

I attach pictures with 3 form waves: square, sinusoidal and ramp. The frequency for all is 22 Hz. And the amplitude is 3 V for High and 0 V for low.

In the pictures there is also the development board LPCXpresso1549 for which I wrote the code. When the signal is captured, the Blue LED must be ON, and the second channel of the oscilloscope shows the DAC output which is proportional with the input signal on channel one. You can see that for the square wave the code is running as expected, the Blue LED is ON, and there is signal on the channel 2, but for the others the Blue LED is OFF and there is not signal on channel 2.

Thank you for your help,
Doini

[kerryzhou · Accepted solution]

Hello Doinita Marcu,

   Thank you for your detail information.

    Now just use the Capture is not enough. You need to associate with the Analog comparators module, use the defined voltage to detect the high level, then after the compare happens, to trigger the SCT and count the timer, then get the input wave frequency. This method can detect all the square, sinusoidal and ramp wave.

    You can try it on your side!

    Any question, just let me know!

Have a great day,
Kerry

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[doini]

Thank you very much Kerry!

I followed your instructions and it works.

(Sorry for the late answer)

All the best,

Doini

[kerryzhou]

Hello Doinita Marcu,

You are welcome!

If you have the new question, welcome to create the new question post.

Have a great day,
Kerry

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