hey i have a project that includes a battery bank with 20 12vdc batteries.
them I would like to be able to monitor separately.
there for I seek a form of a one wire voltage sensor.
or is there a project where I can use a attiny45 as one wire unit.
kim jessen
If you wish to monitor each battery separately you need to appreciate that both battery terminals will be operating at a voltage somewhere between 0V and 240+ (more like 300V). You will therefore require some form of multiplexing system such that the selected battery negative terminal can be connected to the attiny negative reference and the battery positive terminal can be connected to the attiny input terminal (via a suitable potential divider resistor chain)
So, the measurement system is simple - but the means of connecting a single battery to the measurement will be extremely complex.
One method would be to use double pole relays, at least 1 relay per battery, but this would require a separate micro unit to sequence each relay in turn. You then have to ensure that only one relay operates at a time (to prevent shortening batteries) which itself may require further relays.
You might be better having individual attinys attached to individual batteries and then monitor their outputs via individual opto-isolated data lines.
The DS2438 is a special OneWire battery monitor. I don't know if it will work with 12V.
There is also a common ADC OneWire, like the DS2450.
This question comes up about once a year. It results in a long thread with people pitching in their own method. There are no easy answers which ever one you chose.
This is one such thread:-
http://forum.arduino.cc/index.php?topic=134908.0
There are others if you google.
Hi,
Big First Question, how are they wired, all in series or all in parallel?
Makes a big difference.
Tom.... 
..and if they are wired in series I hope you know what you're doing. Get yourself across those and it's "Goodbye Kim!"
Russell.
Have you ever heard of the optocoupler.
Each battery supplies its own module which then sends the data to the main prosesor using the one Wier protecol.
it will work the same way as if you measure across each battery with a multimeter.
I can just not see the big rocket science in it.
Kim
Peter_n!
Thank you it was exactly something like that I was interested in.
Now I need a bidirectional optocoupler which can be used to make the galvanic separation.
and so should the task be done.
many thanks.
Does anyone have a suggestion for an optocoupler?
I have found a few but if you know one.?
Kim Jessen!
Hi,
Can you answer post #4 please.
Tom....
kimjessen:
Have you ever heard of the optocoupler.
Each battery supplies its own module which then sends the data to the main prosesor using the one Wier protecol.
it will work the same way as if you measure across each battery with a multimeter.
I can just not see the big rocket science in it.Kim
Have you ever tried to run a 1 wire bus protocol over an opto isolator?
Or maybe you are going to have a processor on each battery, in which case you need to communicate with 20 serial channels on the controlling Arduino.
Peter_n hehe you are brilliant it looks like the solution.
Tom it is mixed 4 x 5
Grumpy_Mike No has not tried but would try with a bi-directional.
kim.