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Hello

I'm working on a small project where I use stand alone ATmega 168 for some audio and LED fading.
It will be a small pcb that runs on 12v and has a audio line input and output.
A Sharp GP2Y0A02YK infrared distance sensor will be used to control audio volume and LED brightness.
It all works quite well except for the things.

As soon as i plug in the Sharp sensor I get a high pitch sound on the speaker.
I'm not sure why this happens but I think  I need to separate the audio from the power supply.

The second issue is that my 5v power regulator is getting really hot.
Even if the circuit is only drawing about 100mA.

Here is the circuit diagram. Any suggestions?

« Last Edit: August 13, 2010, 05:31:23 pm by tripmaster » Logged

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Even if the circuit is only drawing about 100mA.
In my experience with the 7805 regulator, 100mA is a substantial amount of current not to mention the fact that it has to drop 12V down to 5V. Is it absolutely necessary to run it off 12V? I have connected 12V into a 7805 and ran one LED with a 220ohm resistor and the regulator got pretty warm..
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I just read a similar distance seneor from Sharp. There is an oscillation circuit that drives the IR LED. Not sure why but I suppose the high frequency oscillation on the LED is creating noise and your speaker is getting it. Try to add a cap between the sensor 5V and GND. If you can desolder your sensor and hook up some external wires to it, away from the speaker, see if it works. Do you have a ground plane on your PCB?
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As soon as i plug in the Sharp sensor I get a high pitch sound on the speaker.
I'm not sure why this happens but I think  I need to separate the audio from the power supply.

You might try placing a small capacitor (non-polarized) between the audio inputs/outputs and the DS1809, plus caps across the power supply pins and grounds of the DS1809...

Quote
The second issue is that my 5v power regulator is getting really hot.
Even if the circuit is only drawing about 100mA.

That's because the 7805 is not a very efficient beast, especially when dropping 12V to 5V, as noted. You should really put a heat sink on that device, and maybe a small fan. However, it might be better to look into one of the "new" switcher regulators for replacing the 7805; they aren't cheap, though; see:

http://www.dimensionengineering.com/DE-SW050.htm

...as an example.

 smiley
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Also the TRACO TSR-1 series, up to 96% efficient, up to 36v input with no heatsink required.
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Thanks for the advice.

While working on an other project that also involved audio I recalled that it might be a good idea to get the ground of the audio and the Sharp as far from each other as possible.
So I placed the sensor right next to where the power enters my breadboard and the noise was gone.

I also changed the caps for the 7805. I now use a 100n parallel witch a 100u on the input and a 100u on the output. I let it run for some time and it didn't get very hot.
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