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'[EE]: Quick circuit question'
2001\10\14@163941 by

Hi all. This is going to be a bit odd, but I haven't had much sleep
lately, and I just want to make sure my thinking is correct. I am
designing a simple continuity tester, with a rechargeable battery. I
would like the battery to be charged through the same two terminals it
uses to test with. Because the indicator is an LED, I can't just connect
up a supply, because that would reverse bias the LED and cause no

-----|>|-------                 diode
|             |
|             |
--|<|--/\/\/\-|                 LED + resistor
|             |
|             |
---            |
-----           |                 rechargeable battery
|             |
|             |
o             o                 test/recharge terminals

my theory is that in regular operation, the current will go through the
LED and light it in the event of a continuous circuit. If I apply the
proper polarity recharge voltage to the terminals, it will reverse bias
the LED, but forward bias the other diode, and charge the batteries.
Question is, will it work? What diode should I use so that I might
minimize the voltage drop?

Thanks,

Josh Koffman

--

And a quick follow up question too. What if Instead of a regular diode,
I add in another LED as my "charging" indicator. I would have to
increase the charging voltage to take into account the larger voltage
drop correct?

Thanks,

Josh Koffman

Josh Koffman wrote:
{Quote hidden}

--

Not if you use a regular diode (as picutred, but put
in another resistor/LED combination as pictured, but
in the opposite direction.  This would be another
circuit branch, and not part of the charging loop ...
but will be correctly biased to light when charging).

Good luck,

ATM

--- Josh Koffman <listsjosh3MTMP.COM> wrote:
{Quote hidden}

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--

Thank you! That's just the kind of suggestion that I needed. Do you have
any ideas of what kind of diode I should use for the regular diode? Here
is the updated schematic just to make sure I have it right:

--|>|--/\/\/\--                 Charge LED + resistor
|             |
|             |
|----|>|------|                 diode
|             |
|             |
|-|<|--/\/\/\-|                 Continuity LED + resistor
|             |
|             |
---            |
-----           |                 rechargeable battery
|             |
|             |
o             o                 test/recharge terminals

Josh Koffman

Allen Mahurin wrote:
{Quote hidden}

--
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