PIC Microcontroller based resistor decade box

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. Thatā€™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 ā€œmakeā€ the resistance. Switching resistors with transistors or mosfets gives a high switch resistance and canā€™t handle AC voltages. Thatā€™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.

Part list:
PCB low resistance:

31KR22, R23, R24
11K8R26
31RR1, R2, R3
11R8R5
12K2R25
12R2R4
13K3R28
13R3R7
14K7R27
14R7R6
310RR8, R9, R10
118RR12
122RR11
133RR14
147RR13
3100RR15, R16, R17
1180RR19
1220RR18
1330RR21
1470RR20
2100nFC1, C2
274HCT595IC1, IC3
16TQ2-24VK1, K2, K3, K4, K5, K6, K7, K8, K9,
K10, K11, K12, K13, K14, K15, K16

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About The Author

Ibrar Ayyub

I am an experienced technical writer with a Master's degree in computer science from BZU Multan University. I have written for various industries, mainly home automation and engineering. My writing style is clear and simple, and I am skilled in using infographics and diagrams. I am a great researcher and am able to present information in a well-organized and logical manner.

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