Going further into my pressure sensitive pad project (see:http://arduino.cc/forum/index.php/topic,83887
), I have built a force sensing platform in order to track position and pressure of a finger on a plate.
The platform is based on four 1 kg load cells connected to instrumentation op-amps. The idea is to measure the force distribution on the four sensors according to the finger position on the plate. Please see schematics and picture below.
However I have inconsistent data coming from the four sensors. One sensor seems to be at end of its range even without pushing on the plate, another seems to be at the other end of the range, there's only one providing expected data. I wonder if it has something to do with the electronics or rather with the mechanics.
- could the cable length from the load cells to the op-amps (INA 122) be an issue ? Short cables have a 20 cm length, long ones have a 40 cm length.
- could the load cells be inconsistent amongst themselves ? These are load cells built from China on eBay.
- is it correct to tie the top of the four load cells with a rather stiff plate (8 mm acrylic) or should I use a more flexible material ?
- can I tie both top and bottom of each load cell to a common plate as shown on picture or should I let the bottom free ?
I am also looking for a solution to set an equal distance between each load cell and the bottom plate to set the top plate in the most horizontal position and therefore distribute the initial forces as well as possible. Currently it depends on the screws tying the load cells to the bottom plate only. Maybe I could use a kind of spacer with one screw between the load cell and the spacer and another screw between the spacer and the bottom plate ?
Any help would be highly appreciated.