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Battery Level

NosePickerNosePicker Posts: 54
edited 2008-08-06 21:52 in BASIC Stamp
Does anyone know how to use a basic stamp to read the percentage of remaining battery life of a 12v DC battery?
It does not have to be exteramly acurate but something to tell me an approximate level.
Percent may not be the right word to use either.

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Thanks

NosePicker

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-07-25 16:05
    Look at this discussion of the RCTIME statement: www.emesystems.com/BS2rct.htm.
  • NosePickerNosePicker Posts: 54
    edited 2008-08-06 01:32
    After searching for a MAX471 or MAX472 I found they are now being discontinued. I am not sure but does anyone know if the replacement part would be the MAX4729 and/or MAX4730?

    And as a side note would the later be used for testing the battery level of a 12vDC battery?

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    Thanks

    NosePicker
  • metron9metron9 Posts: 1,100
    edited 2008-08-06 02:01
    You can use a voltage divider to divide the cutoff level to 1.4V the threshold of a stamp pin.

    If you want for example 11.5 volts to be the cutoff then use a 1K ohm and a 140 ohm divider. At 11.5V the voltage will be 1.4V and you have about 10 mA of current.

    If you can apply a load to the battery then test it or make sure you test it when the load is applied it will be more accurate.

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    Think Inside the box first and if that doesn't work..
    Re-arrange what's inside the box then...
    Think outside the BOX!
  • Tracy AllenTracy Allen Posts: 6,664
    edited 2008-08-06 21:52
    NP,

    If you want to monitor the battery voltage, you only need the resistor and capacitor in the RCTIME circuit as described at this URL.

    You don't need the MAX471 or MAX472, which are for monitoring the power supply current. The chips you asked about for alternatives are completely different things, analog switches, not high side current sense amplifiers. There are a lot of possible high side current sense amplifiers available from Maxim, Linear Tech, Zetex and others, however, most of them are available only in surface mount packages. The MAX47x came in an 8 pin DIP, and the output as a current source lent it well to an RCTIME conversion scheme. But again, you don't need the chip if you just want to monitor the battery voltage and not the current.

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    Tracy Allen
    www.emesystems.com
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