Switching capacitors with analog Mux

Thread Starter

E_enthusiast

Joined Aug 20, 2020
25
I was wondering if it is possible to switch the capacitor which with two resistors forms the astable configuration in a 555 timer using a CD4051 analog multiplexer
 

dl324

Joined Mar 30, 2015
11,485
Welcome to AAC!

It depends on the circuit. Post a schematic so we can see if you'd be stressing the switches.
 

ronsimpson

Joined Oct 7, 2019
908
Connect the smallest capacitor directly to the NE555. Then through the CD4051 add more caps in parallel to make larger values. I know you will have to do a little math but; The oscillator will run more stable. The effects of the 4051 will be less.
1597949365053.png
 

Thread Starter

E_enthusiast

Joined Aug 20, 2020
25
Connect the smallest capacitor directly to the NE555. Then through the CD4051 add more caps in parallel to make larger values. I know you will have to do a little math but; The oscillator will run more stable. The effects of the 4051 will be less.
View attachment 215206
Thank you for the advice, I really appreciated it
Current through the multiplexer will be less than 1mA, so it should work.

Cropped, brightened image:
View attachment 215203
Thanks for everything.. appreciated
 
You did not indicate the Vcc value.

The “on” resistance of a CD405x multiplexer is reduced significantly with increasing voltage.
The 555 will support 15 volts, as the CD40xx logic does, so try to use that voltage.
 
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If you only have +5 volt available, use the 74HC4051 version.

I ran precisely into this problem years ago with the CD40xx devices, but the 74HC40xx were an order of magnitude better. From memory.

Google the datasheet for actual values.
 
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