For my project I need a lot of analog inputs that are driven by 12V. Usually that would involve a voltage divider for each input.

I’ve come up with the idea to use a analog multiplexer to switch the input before stepping it down to 3v levels. But most multiplexer IC’s cannot cope with large analog voltages. I would be needing a multiplexer that handles 3.3v digital pins select drive the 12v analog input.

But maybe this would work? : http://uk.farnell.com/jsp/displayProduct.jsp?sku=9664548&CMP=e-2072-00001000

I use the 4051… up to 15v 8 inputs to 1 output

I think you’ll find that the multiplexing works as low as 3 volts … Perfect you only need one voltage divider…

Cheers Ian

Thats wonderful news. Do you need to put 12V at the chip too, or are the inputs tolerant?

Thanks Ian

Unfortunatley Not! Minimum 5vdc supply with vdd+5vdc max analogue signal ie… on 5v supply + 5vdc = max vin of 10 volts analogue in, But even if you supply 15vdc you cant go above with your analogue… as it’s 15v max throughout

CD4051BCN by fairchild…

Cheers Ian

Eeerm I read that twice but I still can’t follow…

How much should I put on the chip (Vdd/Vcc versus Vss/Vee) to drive +12V inputs with a 3v digital pin? Sorry if this sounds stupid, but I am stil a new to this

It just means that you can only raise the analogue in voltage 5 volts above the power rail, but no more than 15 volts…

Just power the thing at 12 volts and use 12 volt signals and stick a voltage divider on the 4051 output and if you supply 0 - 3.3v from the FEZ to the multiplex signals you’ll be good to go.

Cheers Ian

P.S. you okay with the voltage divider?

[quote]Just power the thing at 12 volts and use 12 volt signals and stick a voltage divider on the 4051 output and if you supply 0 - 3.3v from the FEZ to the multiplex signals you’ll be good to go.
[/quote]

Great,thanks. I just wanted to make sure the Fez supply would be enough to drive to signal selectors… Will any 4051 do this or do I need to select a specific supplier? Over here in the Netherlands there’s not much choice in shops/parts and i don’t want to spend \$5 shipping on a \$0.25 part.

Also, yes: I am really getting the hang on this voltage divider stuff.

most CMOS devices will do just check the data sheet your looking for 3-15v digital input as they have level shifters built in…

Cheers Ian

P.S. it also specify’s a different rail voltage

Thanks I will let you know my results