I was thinking about making a resistor decade box, but I found the rotary switches that are used in these most of the time rather expensive and a bit old fashioned. That’s why I decided to use a rotary encoder and select the resistors with a microcontroller.
Now I only had to find a way to “make” the resistance. Switching resistors with transistors or mosfets gives a high switch resistance and can’t handle AC voltages. That’s why I opted to use relays. The currents that need to be switched are rather small, therefore a small relay is sufficient. The relay board is used 2 times with different resistor values.
PCB low resistance:
|3||1K||R22, R23, R24|
|3||1R||R1, R2, R3|
|3||10R||R8, R9, R10|
|3||100R||R15, R16, R17|
|16||TQ2-24V||K1, K2, K3, K4, K5, K6, K7, K8, K9,|
K10, K11, K12, K13, K14, K15, K16
For more detail: PIC Microcontroller based resistor decade box