Arbitrary Waveform

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HD13
Posts: 8
Joined: Thu Sep 21, 2017 4:42 pm

Arbitrary Waveform

Post by HD13 » Fri Sep 22, 2017 10:01 pm

I was looking for a USB/PC scope and stumbled across the Red Pitaya.
I need to use the arbitrary waveform gen for specific pattern.
But can't seem to find or understand if the RP can produce this signal.
Its a low frequency wave and runs between 0Hz-5kHz.
It has 46 regular periods then some pause of 2 periods.
In the automotive scene it is known as an 48 minus 2 vr sensor signal.
See attachment.

If it is posted at the wrong place, could someone replace it ? :)
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JohnnyMalaria
Posts: 28
Joined: Fri Apr 28, 2017 12:43 am

Re: Arbitrary Waveform

Post by JohnnyMalaria » Fri Sep 29, 2017 4:18 am

It is possible but the frequency resolution in your frequency range is very poor. The way the RP works is that you fill a 16K buffer with the waveform and then tell it at what frequency to generate the full length of the buffer. So, if your waveform is a simple sinewave and you want 5Hz and create a waveform with 10 cycles then you'd tell the RP to generate the waveform at 0.5Hz (since 10 cycles every 2 seconds is 5Hz). Problem is...the RP's frequency resolution at this end of its operating range is really (and inexcusably) poor. The nearest you can get to 0.5Hz is something like 0.48 or 0.51Hz. You can't get exactly double that, either. In fact, based on my tests and calculations, it is not until you get above 10kHz that you can get a frequency within 0.5% of what you want.

I strongly recommend you think very carefully about how accurate your desired frequency control needs to be. If, say, you need to sweep from 1Hz to 500Hz in precise steps of 0.1Hz, the RP will not work for you.

Sorry if this is confusing.

John.

HD13
Posts: 8
Joined: Thu Sep 21, 2017 4:42 pm

Re: Arbitrary Waveform

Post by HD13 » Fri Sep 29, 2017 6:01 am

Hello Johny,

Thanks for the only reply.
I'd already ordered the Red Pitaya.

I need it to replicated a crank senor, which in real live are not steady.
They don't hold a precise frequency, crank does accelerate or decelerate depending on which of its four strokes its working in.

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