I have this project in mind for a spot welder where i need to measure the resistance of the attached weld cable. The idea here is to have constant current source using an opamp with its feedback connected to the weld cable to be tested. Initially wanted to do it without re-attaching the cable to another terminal could not figure it out so made it separate.
Here is what i hope to accomplish or could be wrong completely. Once the electrodes are shorted the base of Q7(iSet_EN) is set high by the microcontroller. A voltage drop at the cable would be read at 1 & 1 & 2 of J1 which would be the total resistance of the cable.
The design and function is fairly simple during a weld. MOSFETs Q1-Q6 function as a switch and are driven by their corresponding drivers U1-U6. They switch the stored charge from the supercapacitors C1-C6. These capacitors are in 3s2p configuration with a max voltage of 8.1v. The trigger pulse is send by U8, the Atmega328 from pin 10.
The constant current source is comprised of the opamp U1, U8 send a pulse to Q7 which in turn switches on the power to U7, Q8 base current is controlled by U1's feedback.
Test.pdf (72.9 KB)