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CMOY power level indicator

post #1 of 8
11/15/05 at 6:53pm
Thread Starter 
My son (11 yr old) would like to have me build him a CMOY for Xmas this year. Every time one of his friends comes over he has to show them one of the ones I've made (it's coolness factor for him and he's a science freak). Is there a way to put some sort of indicator on the amp that would remind him he needs to change the battery? I was thinking just some blue LEDs that would turn off when the voltage hit 6.5V or so. The problem at this age is he probably wouldn't notice the amp sounding bad!


edit: Oh yeah, any recommendations for an inexpensive mp3 player to go with this. No way I'm buying him an Ipod to destroy!
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post #2 of 8
11/15/05 at 7:12pm
There is a method for doing just this incorporated into the Pimeta. Take a look at the project page and you should be able to figure it out.
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post #3 of 8
11/15/05 at 7:36pm
Thread Starter 
Quote:
Originally Posted by dsavitsk
There is a method for doing just this incorporated into the Pimeta. Take a look at the project page and you should be able to figure it out.

Thanks. Hadn't thought to look there. I need to try a Pimeta someday.
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post #4 of 8
11/16/05 at 12:25am
Quote:
Originally Posted by Blooze
edit: Oh yeah, any recommendations for an inexpensive mp3 player to go with this. No way I'm buying him an Ipod to destroy!
My 2c: Flash players are very cheap on places like ebay. Sound quality aint mind blowing, and your limited to 512mb - but its a nice cheap mp3 player that will handle almost anything you throw at it.

Rob.
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post #5 of 8
11/16/05 at 12:14pm
Thread Starter 

Low Voltage Shutoff instead?

Quote:
Originally Posted by dsavitsk
There is a method for doing just this incorporated into the Pimeta. Take a look at the project page and you should be able to figure it out.
Would something like this work?
[IMG][/IMG]

Tangent has mentioned using a mosfet to actually shut of the power when it drops to say 6V or so for an alkaline 9V. Never having dealt with mosfet, is there anyone who could give me a heads up about implementing them in this manner.
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post #6 of 8
11/19/05 at 9:03pm
Thread Starter 
After posting this question over at Headwize, I decided it may be better to have a battery cutoff instead of just an indicator. The following circuit was recommended to me and is discussed in the Head-Fi thread "The Lipo Project". I'm not wanting to use SMD size pieces here for the sake of ease of installation (my soldering skills aren't up to it yet).

[IMG][/IMG]

Looked at mouser #827-AME385BEAS for a reference, #595-TLV2401IP for the opamp, but I'm not sure what specs I need to be looking for in the mosfet. This CMOY will be running on a single 9V alkaline and I think a 6V cutoff would probably be appropriate, unless someone could recommend a better cutoff point. Any help would be greatly appreciated.
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post #7 of 8
11/20/05 at 5:29pm
Quote:
Originally Posted by Blooze
I'm not wanting to use SMD size pieces here...Looked at mouser #827-AME385BEAS for a reference, #595-TLV2401IP for the opamp
Personally, I'd look at more generic parts here. For instance, the LM385 for the reference, and the LM358 (yes, confusing names) for the op-amp. For such a simple circuit, cheap parts are just peachy. The only tricky thing about the op-amp is that it be fairly close to rail-to-rail, and be fairly low power. The 358 qualifies.

Also, you're right to go up to a 2.5V reference, or at least consider them. With a CMoy, you're not likely to be restricted to 1.25V references.

Quote:
I'm not sure what specs I need to be looking for in the mosfet.
Low Rds(on) spec, primarily. The ON resistance of the MOSFET will be the impedance of your power supply, so the lower the better. Again, generics to the rescue: the IRF510 can be found at Radio Shack, and has an ON resistance of only about half an ohm.

Quote:
I think a 6V cutoff would probably be appropriate
Only if you are using an active rail splitter. Otherwise, you probably can't get down to that level before the amp starts clipping, with most audio op-amps.

If you are using a low-voltage audio op-amp, then I'd recommend 5V instead.
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post #8 of 8
11/20/05 at 7:51pm
Thread Starter 
Quote:
Originally Posted by tangent
Only if you are using an active rail splitter. Otherwise, you probably can't get down to that level before the amp starts clipping, with most audio op-amps.

If you are using a low-voltage audio op-amp, then I'd recommend 5V instead.
I will probably use a TS922AIN opamp from mouser as I have to put in a good sized order with them and there's not enough on the list to qualify for the minimum at Digikey.

Thanks for the all the suggestions as I've never really used a regulator or mosfet in a circuit that wasn't already designed and tested.
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