/diy/ - Do It Yourself

>>1481380
You need no constant current. I would first use two 1% resistors (e.g. 10K and 100K) connected to a known stable supply like 5V. Then measure the difference with a multimeter and see if it follows expectations. The common mode part can be removed with an instrument amp which has hi Z inputs, no buffers required. The differential gain can then be trimmed with one resistor (R2 in the image). Given the common mode signal of about half a volt, you may not need a negative rail for the amp.