# Is there a demux IC that allows a default signal (not just digital 0) to go to the non enabled outputs?

I am trying to control multiple servos using a Demux and I want the selected output to have one pwm signal and then all of the non selected outputs to receive the same default pwm signal instead of a digital 0. This way all of the non activated servos will hold in one position and only the single activated servo gets a signal to rotate it.

I know I can just do this with logic gates, but if there is a specific IC that does this or there is a name for what I am describing I would like to be pointed in the right direction.

• What is "a signal"? A DC voltage? A fixed PWM signal? Please click the "edit" link under your question ... – Transistor Dec 1 '18 at 23:41
• sounds like a job for a micro-controller – jsotola Dec 2 '18 at 0:18
• all of the non selected outputs to receive the same default signal .... do you realize that you are saying that all the non-selected servos will return to a 'default' or 'home' position .... is that what you actually want? – jsotola Dec 2 '18 at 0:24
• @jsotola I am using a micro controller to create the pwm signal and to control the select lines. I want the non selected servos to return to the same position. That is why I want them to all receive the signal. – Sammy Ochoa Dec 2 '18 at 2:19

## 2 Answers

Use a set of 2-to-1 MUXES.

Most micro-controllers have two or more PWM generators. Thus you can use one to 'move' a servo and the other to 'position' a servo.

To switch between the two you use a 2-to-1 mux per servo where the inputs are connected to the two PWM signals.

Now if you control each mux select signal separately you can switch between the two PWM settings. Your program should make sure that only one select is 'active' at a time to meet your requirements.

any analog mux/demux can have pull-ups or pull-downs connected to the outputs allowing the default to be configured.

or you can use a resistor to pull to a default signal,

• The default is actually a PWM signal, not a logic level. May I encourage you again to capitalise and punctuate properly. Not doing so is sloppy and detracts from the credibility of your answers. – Transistor Dec 2 '18 at 10:33