Bathroom Scale - Wheatstone Bridge

Hi everyone,

So I am looking into/starting a project that requires me to interface an Arduino with a bathroom scale to get a user’s weight. I picked up a Taylor 7058 scale hoping to take it apart and figure out how it works. I think (I could be wrong) the easiest solution is to use the load cells from the scale and to read the weight directly with an Arduino Uno (amplifying the signal with an op amp). I found a pretty decent Inscrutables Tutorial that basically does what I need, but there are a few things it skips over that I don’t understand. I mainly don’t understand the E+, E-, S+, S- of the Wheatstone Bridge.

What confuses me is that there are three wires for each E+, E-, S+, S- giving a total of 12 wires. So do each set of three wires get tied together (All three E+ together, all three S+ together, etc)? I get this impression from the tutorial, but looking at the circuit I don’t think that’s how it’s supposed to be and when checking the existing circuit for continuity with my multimeter between all three E+ there didn’t seem to be any.

If they aren’t meant to be tied together, then why is only one AD260 op amp with one S+, and one S- input used? Also, from the Wheatstone Bridge diagram shown in the tutorial E+ and E- appear to be power and ground am incorrect in thinking that?

Link to Instructables Tutorial (Steps 4 - 10 are about the Wheatstone Bridge):http://www.instructables.com/id/Motivational-Bathroom-Scale/?ALLSTEPS

I have also attached a picture of the circuit board that’s in my scale (not the same exact model as the one in the tutorial), it might be important to also note that my scale runs on 3V (the one in the tutorial uses 5v).

Not shown in the picture on the backside of the circuit board there are 13 vias for the scale’s display to get data from.

scale.jpg

Thanks,

Sean

SRegan:
What confuses me is that there are three wires for each E+, E-, S+, S- giving a total of 12 wires. So do each set of three wires get tied together (All three E+ together, all three S+ together, etc)? I get this impression from the tutorial...

Why would you get that impression looking at this from that "instructable" tutorial:

Google is helpful sometimes, too.

Thanks for posting the diagram, I looked over it again and immediately realized that I originally didn't notice/missed the "W R B" labels in each load cell which made me read the diagram completely differently.

I should be able to connect these properly now, thank you!

Sean