Troubleshooting: Scale

Symptoms

Erratic weight readings that may spike during the hottest part of the day:

Weight reading may swing widely with temperature changes:

Inspect the load cell wiring and HX711 ADC connections.

1. Inspect RJ plugs on load cells. Pins all the same level
2. Inspect RJ Jacks on hive interface board for bent contacts.
3. Replace RJ plugs on load cells with screw terminal connections.
4. Check scale feet for rocking.
5. Test system using the Test Plug described below.
6. Inspect solder connections on the Hive Interface Board and HX711 board.

Inspect RJ Jacks on hive interface board. Bent contacts.

Look inside each RJ jack on the Hive Interface Board. Make sure none of the pins are bent back. A bent pin can be carefully pulled back into place with very thin needle nose pliers.

Replace RJ plugs on load cells with screw terminal connections.

The round black cable on the load cell was not intended to be used with RJ crimp connectors. They almost work but if the wires get crossed under the strain relief, the pressure may cause the wires to short or break. This problem may take weeks or months to show up.

Solder a RJ11 jack on the load cell wires

https://www.sparkfun.com/products/14021

https://www.sparkfun.com/products/132

Test system using the Test Plug described below.

The Test Plug shorts the two inputs on the HX711 and biases them to the middle of their operating range. This will test everything up to and including the RJ jack on the hive interface board.

1. Unplug all the load cells from the hive interface board. 2. Plug in the Test Plug into any jack. 3. Let it record data for at least 24 hours.

Depending on how much the temperature of the HX711 changes, you should see weight changes of +/- .01 kg (+/- .03 lbs). If the load cells were ideal (no temperature dependence and no noise) this is the best the present system can do.

Test Plug Schematic

Test Plug pictures

If the weight changes much more, there is a problem with the HX711 or Hive Interface Board. If this tests good, the problem is with the RJ-11 plugs, the load cells or the mounting.