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

 

Welcome to AAC!

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

 

Welcome to AAC!

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

Is it fine with you if a draw it?

 

Is it fine with you if a draw it?

Any way you want to do it. Photos of screens are the least effective because of moiré patterns; screen captures are better in that case.

 

Any way you want to do it. Photos of screens are the least effective because of moiré patterns; screen captures are better in that case.

 

CD4051 should work OK.
SG

 

Is it fine with you if a draw it?

Illustration is fine- just be clear and consistent in how you draw it, and label everything both with a label like 'R1' for first resistor, and it's value (whether Ohmic, Voltaic, Semiconductor or otherwise).

 

Current through the multiplexer will be less than 1mA, so it should work.

Cropped, brightened image:

 

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.

 

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.
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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:
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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.

 

Yeah the vcc is 5 volt.. so can you please tell me the on resistance of the mux at that vcc value

 

Yeah the vcc is 5 volt.. so can you please tell me the on resistance of the mux at that vcc value

It's in the datasheet. Worst case is 1300 ohms.

Resistance also depends on temperature and signal voltage.

 

It's in the datasheet. Worst case is 1300 ohms.

Resistance also depends on temperature and signal voltage.
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This helped a lot, thanks

 

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.

 

Maybe the switch resistance of CD4051 will be too much, and then you can use 3 N MOSFET, logic level Vgs=5V, MOSFET have a low resistance of Rds.