Hi, all!

I have the top circuit, which is controlled by two manually operated switches. The circuit changes the resistance between points A and B depending on which switch is pressed. I want to replace the switches with a microcontroller, so I designed the bottom circuit. The outputs of the microcontroller are either a digital one, or a digital zero. The only voltage involved is 5 V.


Will this work? What value should I use for the base resistor?


This is just a DIY project — it’s not going to land a rocket on the moon — so I don’t need super precise values. Thanks a lot!

 

The SW01 needs 5.7V into base at least to went into saturation.
Also some Ib current will be added to Ic current (output), so it will cause some output error.

I would use an optocouplers instead bjts and you are good.

 

As an alternative, consider analog switches or a digital pot. Both are easy to use in conjunction with a MCU, and more flexible.

 

use photo FET's and resistors- done.

https://www.digikey.com/en/products/detail/onsemi/H11F1M/1793945

 

Proposed suggestion using a CD4066 quad bilateral switch.
Switch A is normally ON as control A is high through R3 when both micro 1 and 2 are Low. Output = 50K
Micro 1 ON: turns ON switch D, Output = 0 ohms.
Micro 2 ON: turns ON switches B and C.
Switch C turns OFF switch A by pulling control A to ground.
Switch B ON and switch A OFF, Output = 100K

 

You can lose the transistor in the original circuit if you put two 50kΩ resistors in series and put SW02 across one of them.

 

Thank you, everyone! I happen to have some 4066, so I'll try those first.