I've been working on a project lately and running into some hiccups on the latest revision. Basically we are trying to reverse engineer a digital scale. And have made 1 prototype using a load cell (beam type) with a 4 wire interface. This was easy to hook up into an INA125P instrument amplifier and works great.
However, they are very bulky, so we are looking at using a much thinner style 3 wire strain gauge sensor like this for our next version:
https://www.sparkfun.com/products/10245
Very simple in design, and easy to use by itself, but we are trying to use 4 of them (1 for each foot) like in this scale system:
http://www.amazon.com/American-Weigh-ONYX-5K-BK-11-Pound-0-1-Ounce/dp/B001S0ZJUM
Thats where the hangup on how it's supposed to be wired is. As much info as I have gathered, the 4 need to be wired up to make a complete wheatstone bridge. By tying some of the 4 wires together, then taking + and - readings off the others.
The best thread I've found so far regarding wiring 4 of the sensors is this one, but still unclear on how it's done as it seems some of the sensors have to be wired to give opposite readings as the others so they don't cancel each other out? (that was a horrible explanation!)
http://www.nerdkits.com/forum/thread/900/
here is the details of the sensors i have on hand:
resistance readings give me 1K ohm between blk/wht
500 ohm between red/wht
500 ohm between blk/red
and here's a link to my ins amp datasheet:
http://www.ti.com/lit/ds/symlink/ina125.pdf
here's a current diagram of how i have things wired up. no idea if this is the direction i should be heading or not:
on the + side i get a decent swing on ouput of the amp, .06V resting to decent press of .5V on each of the + sensors.
on the - side i get .06V resting, pressing hard on each goes down to .048V
I'm very frustrated at this point, as i know the device is simple, and we already have a working prototype with a similar device, just the lack of documentation on using multiple of these gauges is becoming tiresome. You would think there would be tons of info out there and tutorials. As digital scales, even with 4 sensors, are found everywhere.
Any help is greatly appreciated. My electronics knowledge is definitely mid pack beginner so if I could find a hookup diagram that would be awesome.
Thanks!
Taylor
However, they are very bulky, so we are looking at using a much thinner style 3 wire strain gauge sensor like this for our next version:
https://www.sparkfun.com/products/10245
Very simple in design, and easy to use by itself, but we are trying to use 4 of them (1 for each foot) like in this scale system:
http://www.amazon.com/American-Weigh-ONYX-5K-BK-11-Pound-0-1-Ounce/dp/B001S0ZJUM
Thats where the hangup on how it's supposed to be wired is. As much info as I have gathered, the 4 need to be wired up to make a complete wheatstone bridge. By tying some of the 4 wires together, then taking + and - readings off the others.
The best thread I've found so far regarding wiring 4 of the sensors is this one, but still unclear on how it's done as it seems some of the sensors have to be wired to give opposite readings as the others so they don't cancel each other out? (that was a horrible explanation!)
http://www.nerdkits.com/forum/thread/900/
here is the details of the sensors i have on hand:
resistance readings give me 1K ohm between blk/wht
500 ohm between red/wht
500 ohm between blk/red
and here's a link to my ins amp datasheet:
http://www.ti.com/lit/ds/symlink/ina125.pdf
here's a current diagram of how i have things wired up. no idea if this is the direction i should be heading or not:
on the + side i get a decent swing on ouput of the amp, .06V resting to decent press of .5V on each of the + sensors.
on the - side i get .06V resting, pressing hard on each goes down to .048V
I'm very frustrated at this point, as i know the device is simple, and we already have a working prototype with a similar device, just the lack of documentation on using multiple of these gauges is becoming tiresome. You would think there would be tons of info out there and tutorials. As digital scales, even with 4 sensors, are found everywhere.
Any help is greatly appreciated. My electronics knowledge is definitely mid pack beginner so if I could find a hookup diagram that would be awesome.
Thanks!
Taylor