Super Clean Goertzel Operation With Ultrasonic Transducers

cgracey

Today, I finally got around to trying some ultrasonic transducers with the Goertzel mode in the streamer.

I found a bunch of water-proof 40 kHz ultrasonic transducers in the first box I checked. These are piezo devices, so they don't need any coupling caps for driving or sensing. I connected one as a generator between P0 and P1, which output a differential reference sine at 40 kHz. I connected the other between GND and P8, which was configured as a 100x ADC.

Check out how stable the response is:

All you need is two ultrasonic transducers. No passives needed. Code is attached.

EDIT: Code was updated with improved comments for clarity.

Tubular

Wow thats way better than I would have expected. So glad you found time for that detour.

Which Parallax robot was it that had 8 or more pin sensors around its periphery? Looks like it would be easy to upgrade it

DiverBob

Looking over the code I saw this line: cos,sin := polxy(127, i << -9). What is Polxy()? I don’t see it in the code and it doesn’t show up on the P2 instructions sheet.

evanh

That'll be the Spin2 polar to cartesian conversion. It'll use the cordic QROTATE command.

cgracey

@DiverBob said:
Looking over the code I saw this line: cos,sin := polxy(127, i << -9). What is Polxy()? I don’t see it in the code and it doesn’t show up on the P2 instructions sheet.

It's a Spin2 instruction that converts polar coordinates to cartesian coordinates. It uses the QROTATE instruction in PASM.