For the measurement of the resistance of another PCB I am using a current source seen in the figure below. Now I can measure the voltage with an ADC. With the measured voltage and the set current I can calculate the resistance. After I calculated the resistance I am going to power up the PCB. Now I want to measure the voltage across the PCB. But before I power up the PCB under testing I need to "disconnect" the current source. This way I can measure the voltage and the resistance with the same ADC pin.
Picture from https://cdn-reichelt.de/documents/datenblatt/A200/DS_LM_334.pdf, page 6.
I am going to feed it with 5V, and I need to measure something up to 500k. To achieve this I need a current <= 10uA (5V/10uA = 500kOhm), Let's go for a 5uA max and the circuit can go as low as 1uA. So after the current source I need some kind of switch that's doesn't change the current higher than 5uA.
I am also open for other options like another current-source which can be "disconnected". I just think this is a stable current-source and hope to work with it.