Low Battery Mod Using LM-741

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Mr. Saturn
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Low Battery Mod Using LM-741

Post by Mr. Saturn » Tue May 12, 2009 8:36 pm

Ok guys, I’m in the final stages of building my portable. I’ve got almost everything good to go, there’s just one more major thing I need help with: the low battery mod. Although it’s enticing to leave it out and just enjoy my portable now that it’s functional, I’d really like to have a low battery indicator; I feel like this will make it complete.

I’ve browsed the forum and found Mario’s guide, but I decided to attempt to use the LM-741 for power consumption purposes. I’ve looked around online and found some information, but unfortunately I’m not too familiar with this stuff. I got a diagram and a pinout but I’m having a hard time interpreting and understanding it. The main site I’m using for a reference diagram is the link posted by Rekarp (http://www.reuk.co.uk/LM741-OpAmp-Voltage-Indicator.htm).

I know I’ll need to get the Zener diode(s) for this circuit to work, but the diagram shown for the low voltage indicator does not show them. So, I guess my questions are:

1. Is the diagram for the low voltage indicator (link included above) only showing the part of the circuit that differs from the high voltage indicator (also included on the link above)? To clarify, am I using the same diagram from the high voltage indicator with the only change being off pin 6?

2. Should I even bother using the LM-741, or just use a “2N3904 transistor or equivalent (like 2N2222 or 2N4401)” as described by Mario? What would you all recommend? Is the power saved using the LM-741 significant over the other method?

3. Being the noob that I am, and having a gap in knowledge of electronics, would it be possible for someone to indicate specifically which things connect to which pins? Or explain the diagram from the link (so that it’s clear to me and that I might understand it / learn from it)? This would be a huge help.

If it helps this is what I have for the pinout: 1. offset null; 2. inverted input; 3. non-inverted input; 4. V-; 5. offset null; 6. Output; 7. V+; 8. n/c.

Thanks for all your help. I appreciate everything.

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codeman
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Re: Low Battery Mod Using LM-741

Post by codeman » Wed May 13, 2009 8:53 am

I'll be honest, I didn't read the whole thing. But just a word of warning...you probably don't want to use the LM741. It's not a single supply op-amp, which means you'll need a negative voltage rail for it to work. Search for a single supply op-amp and use that instead.
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Rekarp
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Re: Low Battery Mod Using LM-741

Post by Rekarp » Thu May 14, 2009 4:52 pm

codeman wrote:I'll be honest, I didn't read the whole thing. But just a word of warning...you probably don't want to use the LM741. It's not a single supply op-amp, which means you'll need a negative voltage rail for it to work. Search for a single supply op-amp and use that instead.

mmmm no you don't :|

1. Is the diagram for the low voltage indicator (link included above) only showing the part of the circuit that differs from the high voltage indicator (also included on the link above)? To clarify, am I using the same diagram from the high voltage indicator with the only change being off pin 6?

Yes

2. Should I even bother using the LM-741, or just use a “2N3904 transistor or equivalent (like 2N2222 or 2N4401)” as described by Mario? What would you all recommend? Is the power saved using the LM-741 significant over the other method?

I would use the LM-741. But I am a freak for efficiency.

3. Being the noob that I am, and having a gap in knowledge of electronics, would it be possible for someone to indicate specifically which things connect to which pins? Or explain the diagram from the link (so that it’s clear to me and that I might understand it / learn from it)? This would be a huge help.

The numbers on the yellow triangle are the pin numbers.
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codeman
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Re: Low Battery Mod Using LM-741

Post by codeman » Wed May 20, 2009 5:20 pm

Well just based off my experience using the thing as an amplifier...and reading the datasheet...a negative supply is needed. Also looking at the schematic representation, there are current sources in there that need to be biased with a negative supply. Unless of course you bias your inputs properly, but that would be annoying I would think. Either way, I'm just personally not a fan of the 741 :wink:
What I have shown you is reality. What you remember, that is the illusion.

"Say, what does this button do?"

All the dishes rattle in the cupboards when the elephants arrive

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