Best way to create 16ch ADC on ATMega16?

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#1
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I have an application where I need 16 ADC channels and I am using the ATMega16 which has 8-channels

What is the best way to double the amount of channels? By best I mean part cost/availability/simplicity

I need to stick with DIP parts.

Should I use 8 2-ch analog MUXs?

I was looking at this 2ch MUX:
http://www.futurlec.com/74HC/74H...

My only concern would be I am now multiplexing the analog signal twice (once external of the AVR and once internally) and that the loss may be considerable?

The analog values I will be reading are DC (i.e. I'm not measuring any AC-like waveforms... just the result of a voltage divider)

Thanks
Barron

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Silly idea - a second AVR perhaps? ;)

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Quote:
Should I use 8 2-ch analog MUXs?

I was looking at this 2ch MUX:
http://www.futurlec.com/74HC/74H...

How about using two 'HC4051s (8:1). This combo
can mux one Avr analog input to 16 sources, and
requires 4 digital control lines.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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tpappano wrote:
How about using two 'HC4051s (8:1).

And we use 2 Analog Devices ADG728s. Same idea. Don't quite know why we didn't use the HC4015s.

Stu

Engineering seems to boil down to: Cheap. Fast. Good. Choose two. Sometimes choose only one.

Newbie? Be sure to read the thread Newbie? Start here!

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I'm liking the 2 HC4051s idea and just using one pin on my AVR :)

Thanks.

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Quote:
How about using two 'HC4051s (8:1). This combo
can mux one Avr analog input to 16 sources, and
requires 4 digital control lines.

Err not quite, you need 2 analog inputs on the AVR, one for each 8:1 mux. 5 Digital control lines - 3 addresses and one /ENABLE line for each chip. Using 1 analog input on the AVR you will only get 15 analog channels mux'd and will need only 3 address lines (leave bot 4051 enabled but use one analog line to mux the 8 lines from the second chip)

Why not use 1 16:1 mux. needs one analog input and 4 address lines

Klave

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Hello,
I would use 2x 4051. Use the 'Enable' as your 4th adress line (one enable needs an inverter e.g. transistor) then you can connect both outputs in parallel as one 4051 is always disabled.

Klaus

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Quote:
Err not quite, you need 2 analog inputs on the AVR, one for each 8:1 mux. 5 Digital control lines - 3 addresses and one /ENABLE line for each chip. Using 1 analog input on the AVR you will only get 15 analog channels mux'd and will need only 3 address lines (leave bot 4051 enabled but use one analog line to mux the 8 lines from the second chip)

Quote:
Hello,
I would use 2x 4051. Use the 'Enable' as your 4th adress line (one enable needs an inverter e.g. transistor) then you can connect both outputs in parallel as one 4051 is always disabled.

Actually, you can avoid the need for the inverter by
driving both '51s 3 address bits in parallel, ground
both chip's enables, and run the mux outputs into
two Avr analog inputs. Five total lines, same as if
using one analog input with a chip select line and
inverter.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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A single 4067 would seem easiest to me.

Ralph Hilton

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Quote:
A single 4067 would seem easiest to me.

That would do the job nicely. I just never got
into using the 24 pin devices because the larger
packages seemed more difficult to fit into my
pc layouts. Of course, this was with "dips" back
in the "tape and film" era 8-)

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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I went to put the 4051 into my schematic and realized it was going to take a bit more resources.

I am just going to go with the 4067 and be done with it... I especially dont like the concept of parallell MUX outputs, I am confident it would work fine but I like to keep my analog signals as untouched as possible.

Thanks for the help everyone.