I have a 0-1kg load cell with 4 wires: Excitation + and -, and Signal + and -. I haven't had any problems wiring them up correctly without amplification, and my voltmeter shows me a 1 mV difference between no load and full load (1 kg).
The signal has to feed into an ATmega microcontroller, so ideally I would like to be able to use the full 10-bit analogue scale when reading the values (voltages from 0 to 5 V). In any case, as it stands now, I only get 1 / 1024 as a reading under full load.
I have a prototype deadline for a product soon, and silly as I am I don't have any instrumentation amps left. I tried wiring the signal wires to a general-purpose NPN transistor, but I'm not getting any amplification. This is the transistor configuration that I tried: ignore the double cell symbol for voltage, I couldn't find anything better.
I also tried adding resistors between drain and ground, but that didn't help.
Is there any way I could obtain a usable reading using components I have right now? Ordering a proper In-amp would take too long, and I don't really know what kind of op-amp would be suited for this kind of measurement (although that might be an option).
I don't have a big selection of stuff available, mainly different kinds of transistors. And of course diodes, capacitors, resistors, and the like.