Looking to interface a weighing scale display

Other Hardware Sensors
1

So i am looking for weighing scale from which i can have a digital output.
I started off thinking to design a weighing scale from scratch but this is something that is non-trivial.

The best option for me was to get an off the shelf weighing scale and try to intercept the signal going to the LCD display and the process the data further as need be.

I am looking for something like this.

I'm pretty sure i can simply open it up and read the signal going into the display and get the weight values from it.

Anybody with experience working with displays could help me out figure out the protocol.

Any references would be highly appreciated.

Thanks.
Regards.

2

As always, "it depends". If it had a typical 1602 display it would be doable. If it is designed for low cost and a custom display the controller may be a potted chip outputting row/col to the display, in which case simply accessing all the pins would be tricky.

Also being small doesn't give much to work with. I guess they are cheap, so you might need one to tear apart for analysis and one to use in a final version.

Really there is no way to tell apart from get a device, and start poking around. Bearing in mind you may ultimately be unsuccessful and the only thing gained is a learning experience.

1 Like
3

You are mistaken. This would be as difficult as designing from scratch because it involves re-engineering a commercial product.

Maybe look for a weighscale with a serial/UART or other digital output. These will be more expensive but less difficult to work with.

1 Like
4

I found a teardown https://www.youtube.com/watch?v=Iyh6ZCYQnX0

5

These days, the easier option would be to look for a scale with a bluetooth connection.

6

I found this, may be of interest?

2 Likes
7

I just built one, the answer is in post #6. Use the KitchenScale sample sketch that comes with the library to get you started.

8

Yes I saw that one to seems workable to me

9

So my requirements are high precision, low range load cells.

I'm finding it very difficult to find a load cell for the same. I'm looking for close to 100gm load cells something I'm finding difficult to locate in my part of the world(India).

10

Can you order something like this and scavenge the load cell from it?

But honestly, if you are looking for "high precision" (currently undefined), you should go the bluetooth / RS232 / RS485 / I2C / SPI route. A DIY 100 x 0.01g or 100 x 0.001g scale would be difficult to pull off.

11

Scavenging parts from a new device is my best bet and the route I'm going to go through.

12

By high precision my take is close to a 100gm * 0.01gm weighing scale.

13

Good luck

14

Here's the thing, I got one of these from a local shop, they are battery operated with two(1.5V) batteries my best guess is the excitation voltage for the load cell should be approx 3V(this is my best guess), I'm pretty sure if I use a higher excitation voltage and use a dedicated HX711 as an ADC I think I can get better accuracy.

I plan on using 5V excitation to start with, which I guess will give me better results, how high can I go with these typical load cells I've heard people going as high as 10V and was wondering what are the drawbacks of using high voltages(heating is the first thing that comes to my mind).

15

You should not use a 5v or 10v external excitation voltage with the HX711. Use only the HX711's excitation voltage (about 4.3v). See this for why:

HX711 with external excitation voltage - Projects / General Guidance - Arduino Forum

Read this to understand some of the challenges that professionals deal with when designing a high-resolution weigh scale:

A Reference Design for High-Performance, Low-Cost Weigh Scales | Analog Devices

And if you really want to try the DIY route, you'd do best to get a SparkFun HX711, not one of the cheap green boards.

16

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.