Using another circuit's LCD-output as input?

Projects General Guidance
1

Hi!
Would like your thoughts on interfacing an off-the-shelf scale with an Arduino.
Mainly feasibility & general approach, but all ideas are welcome!

Context
I'm new to Arduino, low-medium experience programmer, built plenty of mechanical contraptions.
Planning to build a semi-automated machine.
The part I'm stuck on is weighing.
I have a 50 g ±1 mg ebay scale which would work fine (combined error 5-8% according to my tests).
How do I get the data from the scale (or its load cell) into the Arduino?

Approach: Jury Rigging the LCD Output
The display is a 7-segment LCD with 6 positions, and a decimal point (DP).
The interface is 14 unmarked leads. I'm assuming that's just a multiplexed 7-segment & DP, and one ground for each number position.

Is it possible to connect these 14 leads to the arduino, and have the Arduino read the signals meant for the 7-segment display as a data input?
I've looked around, but haven't found anyone attempting it. Is it feasible at all (with some work of course), or should I skip this approach?

Approach: HX711
Hx711 interfaces an Arduino to a load cell.
Would this work with the load cell from an off-the-shelf scale?

2

Is it possible to connect these 14 leads to the arduino, and have the Arduino read the signals meant for the 7-segment display as a data input?

Yes but it is quite complex and hardly warrants the effort.

I've looked around, but haven't found anyone attempting it. Is it feasible at all

Well I did it back in November 1987 - it was published in a magazine called The Micro User.

Attached are the text of the article, and the diagrams from it:-

BBC52.txt (11.5 KB)

BBC52D.png
BBC52D.png1129×1923 54.7 KB

3

Krister_Student:
Hx711 interfaces an Arduino to a load cell.
Would this work with the load cell from an off-the-shelf scale?

Can't say. Show us the load cell.

4

The interface is 14 unmarked leads. I'm assuming that's just a multiplexed 7-segment & DP, and one ground for each number position.

It is unlikely that it is this. You need to put an oscilloscope on these leads to see what they are doing.

Can you supply a link to the unit you have bought.

5

Sounds more like a standard common anode or common cathode display, if common anode it can be driven by a TM1637.
Six of those pins will be common for the individual digits; the other eight are for the segments a-g and DP.

6

LCDs are neither common-anode or common-cathode I fear. :astonished: :astonished: :astonished:

7

Paul__B:
LCDs are neither common-anode or common-cathode I fear. :astonished: :astonished: :astonished:

Indeed. Misread that.
Well, waiting for OP to come with detailed info on their specific device.