Electronics > Projects, Designs, and Technical Stuff

ideas for reading a lot of voltages?

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KTP:
I want to build a cell level LVC (and monitor HVC while charging) for my LiMn battery and maybe eventually for a LiFePO4 battery or *gasp* the lightweight but dangerous LiPo packs (I think I would still charge these outside in a gas grill or something even with cell level monitoring  ;)

Anyway, I am going to start simple, and have a Atmel microcontroller monitor the individual cell voltages and disable the electronic brake input to the brushless motor controller on the bicycle if any cell drops below a preset value (the cells are good from 4.1V down to 2.5V but I would like to leave some room and maybe only discharge them to 3V.

Most of the Atmel microcontrollers have just one 8 channel A/D...I don't think any of them have four ports of A/D.  I am thinking I would need to use an analog mux or perhaps hang three more A/D off of a serial data line from the Atmel.  Suggestions?

Filtering on the inputs should not be a problem as I really don't need a fast update (even reading the cell voltages once per second would be acceptable).

After I get this working I will add a few more things, like a shunt to measure peak watts to the motor, average power, and keep track of battery AH consumed.  Perhaps also I will tap off of the hall sensors in the motor to give me a speedometer, and run a serial line to a small lcd on the handlebar.  But starting simple first.

Thanks for any tips

alm:
The ATTiny261/461/861 has 11 ADC channels, I don't think you can get more. Analog muxes would be fine unless they're more expensive than ADC's, since you don't need any speed, multiplexing them is a good solution. Scanners (which is usually a bunch of relays for isolation wired to each channel) are often used for this type of work in automated test setups.

NiHaoMike:
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1786,P87985

KTP:

--- Quote from: NiHaoMike on July 10, 2010, 04:19:17 am ---http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1786,P87985

--- End quote ---

Neat part!  Way overpriced though ($14 for 1-100 quantity).  I could have 4 AVR chips and measure 44 cells for less than that.  I still need to look up how much serial A/D chips are (or the analog mux).

EEVblog:
Use the parametric search and sort by number of ADC channels. 3 devices have 16 channels.
http://atmel.com/dyn/products/param_table.asp?family_id=607&OrderBy=1169&Direction=ASC#760

As do most of the XMEGA AVR's.

Dave.

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