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RE: [SeattleRobotics] Low battery indicator?

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  • Bryan Minugh
    Is your voltage regulator one of the newer low-dropout types (needs only 5.5volts in for a 5 volt output). If instead you have one of the old designs (like
    Message 1 of 2 , Jul 31, 2000
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      Is your voltage regulator one of the newer "low-dropout" types (needs only
      5.5volts in for a 5 volt output). If instead you have one of the old designs
      (like the 7805 and LM340-05) the output sags if the input falls below about
      7 volts. A green LED goes dark if it's leads see less than 2.1 Volts. I
      guess if you connected a green LED (with a series resistor) from the input
      side to the output side of your (old?) regulator it would go dark about the
      time the regulator is dropping out. Although the current through the LED is
      passed around the regulator, it shouldn't upset the regulation if the
      minimum load is always more than the LED current.

      The LED goes dark when the battery is low, instead of lighting up (the
      opposite of the action you asked for), but it is a simple design (just an
      LED and a resistor) that puts no additional drain on the battery.

      -Bryan Minugh

      -----Original Message-----
      From: Gray Chris [mailto:GrayC@...]

      A real cheap solution is to just make a comparitor using an op-amp or a
      comparitor and compare the unregulated voltage to a resistor divider
      reference setup using your regulated voltage.

      Chris.


      -----Original Message-----
      From: macmen@... [mailto:macmen@...]
      Sent: Monday, July 31, 2000 3:43 PM
      To: SeattleRobotics@egroups.com
      Subject: Low battery indicator?


      I would like to add an LED to my PCB that will light when the
      main battery is discharged to a preset level.

      Lumex makes a low battery indicator (SSL-LX5099LBI-SRD) that
      is in effect an adjustable-voltage indicator that lights when the
      voltage drops below a preset level. Is there a better solution
      available? If I were to use this indicator should it monitor the
      unregulated voltage in or the regulated five volts (i.e. with the
      detection voltage set to 4.95v)?

      Any suggestions would be appreciated.

      Greg Schumacher
      macmen@...
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