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The led is off until it hits a threshold low voltage then comes on telling you its time to change batteries. |
Gee, that looks familiar....
In fact, I "invented" that one, too...I added the comparator's output pullup resistor after finding that it never entered the green state without it. I considered the one-color behavior a bug, since I'd gone to the trouble of using a bicolor LED.
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I was about to build something with one but using a not logic gate to reverse the power |
Yes, I briefly considered using digital logic, but analog seems a lot better suited to the problem.
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A comparator shouldn't really oscillate - that's what the histeresis |
I wasn't aware that comparators with hysteresis built in existed. The LM311's datasheet specifically recommends adding hysteresis if you get oscillation. In my case, oscillation would be a minor feature, so I ignored the issue.
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For something to give one a little more info as to battery level, the circuit I made here is usefull. |
Indeed. I guess that chip was made to be used with bargraph modules. Interesting use of discrete LEDs instead.
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Hadron, I like your solution. It isn't much more compllicated or expensive or size-consuming than tangent's |
The use of a voltage regulator as a reference is an interesting tradeoff. A zener's adequate for the job, but it requires 1-2mA so it's not too "soggy". That regulator probably only requires 0.5mA in the adjustable version. But you do pay for it! The adjustable one is only available in 8-pin packages, and it runs nearly $3. Me, I think I'll burn the current and save the cash. I might change my mind if I needed a highly accurate voltage set point, which zeners can't provide.
It's a good circuit, hadron. A little excessive for my immediate purposes, but still interesting.
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I finally managed to get it to work |
Very nice. Economical. It's probably lower current than my design as well. I like that it doesn't blink at three-leg parts, too.
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I've had some good results using Panasonic voltage detectors such as in this circuit: |
I had that in mind when I wrote about blinking indicators above. My specific problem with those Panasonic monitor ICs is that they don't come in very high voltages. But, you could combine the blinker circuit with some of the others in this thread.