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| Battery pack voltage monitor with I2C or SPI |
 Posted: Tue Jul 27, 2004 3:52 pm |
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Hi,
any know of a IC that can monitor a single battey voltage, ideally with I2C or SPI interface, Ideally I want a small IC that has an interface so I can read the voltage from it, I want to have several of hese so I can monitor a battery pack in series.
Thx |
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Ttelmah
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| Re: Battery pack voltage monitor with I2C or SPI |
| Posted: Wed Jul 28, 2004 2:23 am |
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| Guest wrote: | Hi,
any know of a IC that can monitor a single battey voltage, ideally with I2C or SPI interface, Ideally I want a small IC that has an interface so I can read the voltage from it, I want to have several of hese so I can monitor a battery pack in series.
Thx |
Seriously, ADCs, are allways going to be more expensive, than multiplexers. Remember, that if you have an ADC, reading the voltage across a battery, if it is also going to communicate using I2C (or indeed any digital bus), then the 'ground' of the chip, will need to be at the system 0v (or the unit will require optoisolaton). So you would then need an ADC, that supported 'differential' measurement, and had an input voltage range, covering the voltage at the 'top' of the battery pack. These are all features that make a device expensive.
It'd be far cheaper, to simply use an analog multiplexer, with a single ADC, and sequentially read the voltage at the top of battery1, then at the top of battery2 etc.. This is the approach used by the micro based fast battery charge IC's.
There are several simple I2C AD converters, that can be used with a suitable multiplexer to do this, or (of course), the internal ADC, on most PICs is also capable of this (remember in either case, you will need a scaling divider to bring the input range below that acceptable to the IC.
The Philips PCF8591 is a 8bit ADC, with four input multiplexer, which is typical of the type of IC normally used for this sort of application.
Best Wishes |
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