Saturday, September 5, 2020

Airball probe v8 update

It's been a while since there's been an blog post! Sorry for this. I've been completely slammed at work, and just putting in tiny bits of work on the project here and there. But we've been making progress!

This is the newest design for the probe, the "v8" mechanical and electronic form factor:

We are trying out the new scheme of having a 5th hole at 90 degrees at the bottom of the probe nose, to avoid having a bulky static probe. If that doesn't work out, we can always return to the old static probe without much change to the sensors (there's one sensor that would need to be swapped out for one of a different range, but that's minor).

This is built around a 1.5" x 3.5" circuit board that integrates an ESP32-WROOM-32U module, a Bosch BMP388 barometer, 3 slots for Honeywell SPI HSC pressure sensors, a battery charger, and a USB interface.

The temperature sensor is a TI TMP102, which is supposed to be on a tiny daughterboard. For now we don't have that and are instead jury-rigging a TMP102 breakout board stuck to the outside of the probe. The result looks like this:

The circuit board has two known bugs; everything else seems to work:
  • Missing a pullup resistor for one of the USB comms signals
  • The pressure sensors are too close together and so the plumbing is very poor
The mechanical parts need some more development to make them suitable for being a "kit", but they are getting there. Check out this album to see the process of assembly.

Link to photo album: Airball probe v8

Stay tuned while we get this working. Note that this signals a departure from the XBee comms we had previously: This one is just plain Wi-Fi. The plan is to have this thing set up a Wi-Fi base station with a unique name, and you can jump on that and telnet to a known host and port and get a stream of data messages. We tried UDP but we were getting a lot of losses; we might try that again.

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