Reading the HX711 using RMT

[Andreas]

Continuing the discussion from Reading the HX711 using SPI:

Introduction

@weef

A protocol like the HX711 is actually something to deal with the RMT in ESP32, similar to how Boris Lovosevic did for DHTxx and 1wire.

@weef

On another ESP32 board I am currently testing the Loboris-ESP32-micropython variant. With this, the support for DHT and 1wire is already implemented using the RMT peripheral.

@Yann Vernier

LoneTech
Dec 9, 2016, 11:34 PM

While I’ve had success porting the prior micropython bitbanging onewire code (it was mostly changing the IO mode to open drain, and replacing pyb with machine), I just managed to wake up the RMT peripheral. It could conceivably run onewire with extremely precise timing without requiring much CPU. It should only require two RMT channels (one input, one output) mapped on the same GPIO, set to open drain. 6µs should be no problem at all considering I achieved 0.05µs for the WS2812 :)

My initial RMT access code is at GitHub - lonetech/LoPy: LoPy code (MicroPython on ESP32 module).

– https://forum.pycom.io/topic/303/ds18b20-temperature-sensor/14
– Timing things on MicroPython for ESP32 - #8 by Andreas

@David Antliff

This component includes two methods of bus access - delay-driven GPIO and RMT-driven slots. The original implementation used CPU delays to construct the 1-Wire read/write timeslots however this proved to be too unreliable. A second method, using the ESP32’s RMT peripheral, results in very accurate read/write timeslots and more reliable operation.

Therefore I highly recommend that you use the RMT driver. The GPIO driver should be considered deprecated.

– GitHub - DavidAntliff/esp32-owb: Maxim One Wire Bus driver for ESP32.

[Andreas]

State of the onion of RMT library support for MicroPython

Pycom MicroPython

It looks like Pycom MicroPython already supports it out of the box.

https://docs.pycom.io/tutorials/all/rmt/

Genuine MicroPython

Matt Trentini is actively working on an ESP32 RMT Implementation for Genuine MicroPython, see also https://forum.micropython.org/viewtopic.php?f=18&t=7135#p40635.

LoBo MicroPython

@weef

Currently testing the Loboris-ESP32-micropython variant. With this, the support for DHT and 1wire is already implemented via RMT peripheral.

@Boris Lovosevic

This class includes full support for Onewire devices using the ESP32 RMT peripheral to achieve very precise timing.

– onewire · loboris/MicroPython_ESP32_psRAM_LoBo Wiki · GitHub

• esp_rmt.c
• owb_rmt.c
• machine_ow.c
• machine_dht.c

See also

@Matt Trentini

Some progress is being made […]. I’ve got an open RMT PR that I’m hoping to sneak in before the next release to at least provide basic transmit functionality.

– what features would you like to see backported to mainline MicroPython · Issue #304 · loboris/MicroPython_ESP32_psRAM_LoBo · GitHub

[Andreas]

@Matt Trentini

Some progress is being made […]. I’ve got an open RMT PR that I’m hoping to sneak in before the next release to at least provide basic transmit functionality.

Matt’s PR received some more tidying and further development during the past few days.

ESP32 RMT Implementation

[poesel]

FYI the RMT driver is in uPy 1.12 and its working. It would be ideal for the HX711 driver but the problem is that there is no way to get the state of the clock pin when using the RMT driver (at least I haven’t found one). But that is necessary to synchronize with the data pin.