Mini 5+ and DHT21 sensor

oc_geek

I've configured a DHT21 sensor on the Mini 5+
M308 S10 P"spi.cs1" Y"dht21" A"Chbr Temp [C]" ; Set DHT21 for chamber temp
M308 S11 P"S10.1" Y"dhthumidity" A"Chbr Hmdy [%]" ; Set DHT21 for chamber humidity

it is connected to the TEMP DB header for GND/3.3V and SPI2.CS1

However it reads 2000 C and 2000 %

pkos

I haven't tried that on my mini 5+ yet, but are you sure it shouldn't read spi2.cs1 in your M308? You only have spi.cs1.

Also - make sure you have the newest firmware (3.2.2). 3.2 had a regression bug that caused DHT2x to not work and show 2k all the time.

oc_geek

@pkos i thuoght SPI2.CS1 too but it tells me it does not exists... naming are a bit ...naive

pkos

Ah right. Then check 3.2.2 - it fixes the DHT problem

oc_geek

no it does not fix the issue

pkos

I'll be working on my mini 5+ tomorrow. If nobody gives you any good hints before then I'll take a look to see if I can get the DHT to run.

oc_geek

@pkos thanks !

dc42

I confirm that there appears to be a problem with DHT sensor support on the Duet 3 Mini. I have configured a DHT22 on pin spi.cs2. I can see the firmware requesting a reading and the sensor responding, but it looks like the firmware isn't picking up the response.

dc42

I found the problem. The spi.cs# pins on the 3 Mini don't support interrupts. I am looking for alternative pins to use.

oc_geek

ok thanks... will be then the third time i redo the connector LOL

dc42

The solution will be to connect the DHT sensor to one of the 5-pin IO connectors. The signal wire will need to be connected to both the iox.in and iox.out pins. The Vcc and ground pins can be connected to 3v3 and GND on the same connector. The firmware support will be in RRF 3.3beta1, due to be released shortly.

oc_geek

ohh great that's where it was before... damn cut again and rewire

So i have to Y the signal to BOTH in and out pins ?

@dc42 and the configuration in firmware what pin would it call in
Sxx P"..." ?

P.S. I think you would concur that this a pretty weird wiring setup... wonder how come the cs pins are as they are...

thanks

dc42

The issue is that on the MCU used in the Duet 3 Mini, only some pins have a pin change interrupt facility. We assigned the available interrupts to input pins. However, the input pins have a 10K series resistor to make them tolerant of high input voltages, so they can't be used as outputs in this application.

The configuration line you will need is this or similar:

M308 S10 P"io4.out+io4.in" Y"dht21" A"Chbr Temp [C]" ; Set DHT21 for chamber temp

I have this working now.

oc_geek

wow in + out LOL would never have thought about that

my wires are ready !

thanks

dc42

This is now released, see https://forum.duet3d.com/topic/21597/reprapfirmware-3-3beta1-now-available.

oc_geek

@dc42 Thank you for the prompt feedback. Will check it out, test and report back

MikeS

@dc42 just to clarify the daughter board cs pins can be used if 10k resistor is unsoldered and pads are bridged? or all daughter board cs pins can't handle interrupts?

oc_geek

@MikeS which daughter board do you ref to ?

oc_geek

@dc42 said in Mini 5+ and DHT21 sensor:

M308 S10 P"io4.out+io4.in" Y"dht21" A"Chbr Temp [C]"

tested with Rel 3.3 Beta 1

it is working now, thanks

MikeS

@oc_geek i thought you were using the daughterboard connection for the DHT which is made to be used with this: https://duet3d.dozuki.com/Wiki/PT100_temperature_sensor_daughter_board. Now i saw that you used the 12864_EXP* one. I don't understand if all expansion / daughterboard SPI pins can't use interrupts, or maybe some have it but they have the 10k resistor. In the second case the resistor could be unsoldered and, with the pads bridged, only one pin used for I/O.