HX711 scale fluctuations

[Asco]

Hello,
I'm discovering ESPEasy which is fantastic!! Thanks to all the developers!

I' have some troubles to use a HX711 to make a scale with the ESP_Easy_mega-20180624_test_ESP8266_4096.bin
I' have tried several bin but I always have the same troubles.

My ESP8266+HX711 works well if I use an arduino sketch with the lib <HX711.h> ; I get stable readings.

If I use ESPEasy, without touching the scale, I get:

Code: Select all

3552: WIFI : Connected! AP: NETGEAR94 (9C:3D:CF:2A:98:E6) Ch: 8 Duration: 2905 ms
10649: HX711: Value: -319.969 = 3502217.500
20649: HX711: Value: -344.875 = 3737986.500
30649: HX711: Value: -363.437 = 3913704.000
30654: WD : Uptime 1 ConnectFailures 0 FreeMem 20656
34537: WIFI : DHCP IP: 192.168.1.20 (ESP-Easy-2) GW: 192.168.1.1 SN: 255.255.255.0
34540: Webserver: start
40649: HX711: Value: -337.625 = 3669356.000
51161: HX711: Value: -329.406 = 3591555.500
60654: WD : Uptime 1 ConnectFailures 0 FreeMem 17848
61161: HX711: Value: -342.594 = 3716391.500
71161: HX711: Value: -346.719 = 3755440.000
81161: HX711: Value: -315.625 = 3461098.500
90654: WD : Uptime 2 ConnectFailures 0 FreeMem 17824
91161: HX711: Value: -288.687 = 3206101.500
101161: HX711: Value: -330.187 = 3598951.000
111161: HX711: Value: -329.437 = 3591851.000
120654: WD : Uptime 2 ConnectFailures 0 FreeMem 17848
121161: HX711: Value: -334.812 = 3642732.500
131161: HX711: Value: -338.562 = 3678230.500
141161: HX711: Value: -342.187 = 3712546.000

Who can help me to find what is wrong with this?

Thank you in advance!
Chris

[TD-er]

The power supply of the ESP may become noisy, due to its power demands.
I can imagine the ESP will be doing a lot less work when using a sketch that only does this reading. ESPeasy does do a lot more in the background.
How is the HX711 powered?

[Asco]

Hi Td-er,
Thank you for your help!

The HX711 is powered by a 3.3V pin of the ESP8266...I think you re right.
I'll try to do another way.

Thanks!
Chris

[osoon]

Hi Td-er,
Thank you for your help!

The HX711 is powered by a 3.3V pin of the ESP8266...I think you re right.
I'll try to do another way.

Thanks!
Chris

any luck of getting stable readings?

[Asco]

Hello Osoon,
now it works perfectly, it was because I was using a too small USB powersupply (not enought current).

Thanks

[chunter1]

How stable is "stable"?
I get these readings when using two 50kg weight-cells on channel A (gain 128, no oversampling):

Code: Select all

727944: HX711: GPIO: SCL=13 DOUT=14
728119: HX711: Value: 144.000
729119: HX711: Value: -7.000
730119: HX711: Value: 51.000
731119: HX711: Value: 53.000
732119: HX711: Value: -36.000
733119: HX711: Value: 27.000
734119: HX711: Value: 55.000
735119: HX711: Value: -16.000
736119: HX711: Value: 32.000
737119: HX711: Value: 33.000
738119: HX711: Value: -13.000
739119: HX711: Value: 16.000
740119: HX711: Value: -31.000
741119: HX711: Value: -80.000
742119: HX711: Value: -47.000
743119: HX711: Value: -42.000
744119: HX711: Value: -34.000
745119: HX711: Value: -59.000
746119: HX711: Value: 26.000
747119: HX711: Value: 16.000
748119: HX711: Value: 60.000
749119: HX711: Value: -38.000
750126: HX711: Value: -48.000
751119: HX711: Value: -61.000

I even observe a drift over time although the sensors are not moving or stressed in any way.

[chunter1]

I recorded several hours of sensor data.
The setup did not move and the temperature changed not significantly aswell.
So...I don't know what's going wrong here.

[chunter1]

Looking at the schematic and checking the PCB i found two design flaws (besides the generally totally inadequate design for a 24 bit ADC):

1.) AGND is not connected to the GND pin!! You need to make your own connection otherwise it is undefined and only connected through some body diodes!

2.) The HX711 datasheet says, that AVDD should be at least 100 mV lower than DVDD.
The resistive divider on the board however is only dimensioned for 5V supply resulting in 4.3 V.
By replacing the 8k2 resistor with a 15k the LDO now sits at 2.9 V for AVDD which is fine when using it with a 3.3 V supply.

It's funny that these crapy GREEN chinese HX711 PCBs are sold all over the places and only a view people seem to care
Next time i'll try something slightly better looking like this shielded and at least symetrically filtered one: