I'm bending a small book strip and I'm trying to add a power switch with an LED to show the unit is turned on. The power switch seems to be working fine, but when I test the LED in line, it cuts all audio from the unit. The LED does light up when the unit is powered on, though. I've tried placing it in several different points on the circuit and it does the same thing every time. Does anyone know why it would block audio like that? Is there a different way you're supposed to wire up a power LED that I'm not aware of? Any help would be greatly appreciated!
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Can I see a picture of how you're wiring this? I don't know exactly what you're circuit bending, but there should be a regulated power source, and you should be soldering the LED to that with the appropriate resistor. Keep in mind that a single LED with the incorrect value resistor is capable of drawing enough power to cause things like audio failure, or worse.
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I took a photo, but I'm not sure how to add images on this forum. What I'm bending is from of a children's book that has a simple audio device attached. All it does is play sounds when you press the buttons. It's very basic.
I'm relatively ignorant when it comes to incorporating LEDs into projects. The way I have it right now, I just clipped the wire coming from the positive battery terminal and inserted the LED in line. Are you saying I should be including a resistor in this setup?
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Sea of Souls
That's almost as bad as what Apeshit thought you did. In this case, you're powering the existing circuit with an LED voltage drop which can be 1.9v to 4.0v for green LEDs! The reason your LED doesn't burn out is because the circuit load acts like a resistor and the reason why your audio dies is because there isn't enough voltage after the voltage drop.
Solder the power cable back to the way it was originally. Then wire a resistor between the power source and your LED's anode, then wire the LED's cathode to ground. Start with 1k resistance and if it's too dim, try a smaller value.
Is that thing powered by one or two coin cells batteries?
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Thank you! That solved the problem. I'm still pretty ignorant about certain components, so that was a good lesson.
It's powered by three coin cell batteries, by the way. Would it be better to replace those with larger batteries?
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Sea of Souls
southboundpachyderm wrote:
Thank you! That solved the problem. I'm still pretty ignorant about certain components, so that was a good lesson.
It's powered by three coin cell batteries, by the way. Would it be better to replace those with larger batteries?
I wouldn't just replace the batteries with larger ones. There are different voltages after all. If you can calculate or measure the voltage of all three batteries together, then you can figure out which batteries are safe to use. I'm guessing the batteries are in series and are 1.5v each. You'll get longer life with bigger batteries and can effectively add more components like LEDs, but you need to match that voltage since there probably isn't a voltage regulator per se. If the batteries are 3v and measure 9v in series, then a 9v battery will be fine to use and get you longer life. If the batteries are only 1.5v in series then you can either use AA or AAA in series to get 4.5v.
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Okay, thank you. The batteries are 1.5v each, so I think I'll upgrade to three AAA batteries.
One more question...I notice the power LED dims when there is audio output. Do you know why that might be happening? And is there any way to prevent that?
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Sea of Souls
AAA's will provide more current than the coin cells, so that should help with the dimming.
To be honest, we have to assume it is an unreliable power source. The audio circuit probably takes everything it's got just to work, so dimming of the LED is expected. Whats happening is that once all of the available current is being drawn, the voltage begins to droop. So if there is more current available, the voltage will remain more stable.
There are a few things we can do once you swap in some AAA's.
1. you can increase the resistor value.
2. you can wire a transistor in the mix to regulate the amount of current the LED gets.
But you may not need to do either of these once the power supply has more "juice" to offer.
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I switched to AA's and you were right - it decreased the amount of dimming on the LED considerably. It also changed the sound quite a bit, and in a really interesting way, so I'm thinking I'll add a switch to be able to go back and forth.
When I increase the resistor value (right now I'm using a 470 ohm), the LED becomes too dim overall. The transistor solution sounds interesting. How would I wire that up?