Load Cell Sanity Check

Projects General Guidance
1

I have an unlimited supply of generic Chinese load cells, given to me by my employer. They are 4-wire (black, white, red, green). I know they work quite well as I've used them in other projects before.

I want to simply calibrate them (some weight should read 0 with less weight being negative) and then average the readings and send out a data point every 8 seconds with Bluetooth that can be graphed by a laptop or a phone.

Thinking of buying an HX711 amplifier and an s3 dev board. Are these reasonable options? Is that all I would need?

Thanks

2

A link to their datasheet is requested.

No. You need powersupply according to the components. Breadboard for testing or protoboard and soldering.

3

Buy an Arduino that has 5V I/O

1 Like
5

What do you recommend?

6

An Uno.
You will find dozens of tutorials and libraries for using the HX711 with an Uno.
Do you really need Bluetooth?

1 Like
7

Yes, the phone can't be required to plug into the Arduino, and it needs to be able to work in places without internet.

8

image
image1920×2560 268 KB

9

Well the S3 only has BLE (Bluetooth Low Energy), I've never used it.
You will need a 5V supply for the HX711 and the S3 and some level shifters to interface the HX711 with the S3

10

Thoughts on the NAU7802 instead of the HX711?

11

If you think you will be using 5V logic enough you could go with a Uno + the Adafruit BLE shield with has 5V safe inputs. Having a Uno in your collection is never a bad idea.

12

Well give me a few days to compare the performance of each device.
Are you experienced at making PCBs?

13

Unfortunately not at all. I've only just learned to solder haha.

14

You will need a special HX711 board that also can do 3.3volt processors.
Sparkfun is AFAIK the ony one that sells a 3.3volt-logic compatible board.
Note the two supply connections; VCC and VDD.
5volt for the load cell amplifier and 3.3volt for logic.
Leo..

15

A sensitivity of 0.6 mV/V isn’t that great

16

For a 100g loadcell it is.

17

One I scavenged from a commercial 100 g scale was close to 2 mV/V. At 0.6 mV/V and 4.25 v excitation, only 15% of the HX711’s range will be engaged. That’s not great, but it may be good enough for the OP.

1 Like
18

Looks like a good alternative to the HX711 for 3.3v processors.

19

The STEMMA connector sort-off forces you to use a lower excitation voltage, so lower output and more noise from the load cell. Because the built-in progrmmable LDO can only output a lower voltage than the board's supply.
Easier, but not sure if this NAU7802 board is better for 3.3volt processors than a HX711 with two supply connections.
Leo..

1 Like