[arnolde]

Filter? Of course not, you want a clean square wave signal, you dont measure the voltage (it's not PWM) but you measure the frequency, and calculate the voltage from that. It's much more precise, and easy to do with a µC.

Personally I got some MCP3909 because they go from -1V to +1V, but then I found out they don't put out the signal in such a nice way as I want. I dont know any others to recommend, just call up any decent electronics website (newark?) and search for "volt 2 freq" and there will be about 10 types to choose from, and read the datasheets...

The MCP3909 seemed ideal because they each have 2 A/D inputs, already laballed "current" and "voltage" but it seems the 2 normal freq.outputs are not seperate outputs of these seperate values, but in fact the chip calculates "power" from the inputs and puts that out instead. On the SPI output however, it will output both in "clear". But there is more decoding necessary on that one, and it's meant for higher frequencies (1mhz) and Im not sure if I can go slow enough. Anyway I'm a little confused by the datasheet and so I'll just have to try them out.

Another approach, of course, would be to just stick a µC with A/D ports onto the measurement circuit (instead of the v2f) and output direct values in clear text via opto-isolated RS232 serial, and that can be sent to a) the charger logic and b) a cockpit instrument. Actually.... hmmm... that sounds even better. I think I may well just do that. I just thought of that myself :-) only drawback is, that part then isnt isolated from the pack so you have to disconnect it when messing around with it (updating firmware, etc.)