Puck.js hardware talk

Hi!

what was the reason for switching to the MMC5603NJ magnetometer in rev 2.1?

Sadly the component shortage - plus some customers used older firmware on Puck v2.0 and 'bricked' it because of the usage of the reset pin for the LIS3MDLTR

Component availability for ST chips is awful right now. We're still using LSM6DS3TR-C but for the batch we're making now they were very hard to find and I had to pay double price for them.

The second question is somewhat related: since the 2.1 schematic is not publically available, what is the pin configuration of the MMC5603NJ? Is the reset pin of the NRF52 free again and the SDA and SCL the same as on the LIS3MDLTR in 2.0?

Yes, that's right - sorry - I just put it live at https://github.com/espruino/EspruinoBoar­d/tree/master/Puck.js/pdf

Third question: as the red LED is the light sensor, what is the "infrared in" pin used for? Does it actually work as a receiver or a sensor?

That was the intention, but sadly I never had any success with it. It may be possible to set it up using the PPI peripheral to charge the LEDs and count how long they take to discharge with https://www.espruino.com/NRF52LL#hardwar­e-capacitive-sense-on-two-pins but I haven't had time to try that.

It is however useful for the self-test, since the Puck can check that the IR leds are attached and that the FET is working.

Have you considered using a BME280 or so as the temperature sensor?

Yes, but the BME280 is £2.89 at 500-off, PCT2075TP is £0.35 - so it's a lot pricier.
And on top of that the case is sealed-ish, so the Humidity and Pressure aren't that useful. It didn't seem worth adding extra cost to the Puck for a feature that users would have had to have drilled a hole in the case for :)