# Input voltages to multiplexers

1. Nov 21, 2008

### BillyBobjoe

Hi All

I am wondering does anyone know the voltage limits of standard mux such as 74151A.
I aim to place diferent voltage levels into the mux and select one input as the output that will go to an ADC. The voltages will be of increasing values i.e 4V, 8V, 12V 16V etc. Is 16 Volts too much to go into an input of a mux?
If 16V is ok, is then placing this 16 Volts into an ADC allowable or is it two much

Thanks

2. Nov 21, 2008

### Proton Soup

it appears to be a digital MUX http://www.tecnoradio.com.br/eletronica/datasheets/74XX/%20DM74151A.pdf [Broken]

Last edited by a moderator: May 3, 2017
3. Nov 21, 2008

### Staff: Mentor

So if you want to MUX analog voltages, you will need to use Analog Switches or Analog MUXes. You can google those terms to get a selection of parts, or go to Analog Devices and Maxim's websites to find some typical parts...

4. Nov 22, 2008

### MATLABdude

Most analog switches (and ADCs for that matter) will have an absolute voltage input of 5V (or less, depending on what it takes in as a supply voltage).

You could use an array of relays (fun AND noisy!), but you'll still run into the problem of how to sample these large voltages with the ADC. Usually, a voltage divider scales down the voltage to an acceptable level (which can actually be sampled).

Could you elaborate on what you're trying to do with this switching network, and why you need those voltages?

5. Nov 22, 2008

### BillyBobjoe

the basic idea was to use a microcontroller to perform calculation with these voltages. The voltages need to be digital going into the microcontroller therefore the use of the ADC.

Is a voltage divider the best way of performing a sort of step down ratio? Its needs to be power efficient. The use of multiple Dc-dc cobverters proberly wouldn't be too efficient either would they?

6. Nov 22, 2008

### uart

Yes it's normal to scale the voltages with voltage dividers in this situation.