SparkFun Forums

[thankyou]

I was wondering if a tinyAVR that only needs 0.7V to operate could use an audio signal as the power source. I am using the Sparkfun 3.5 mm audio jack breakout board, and if I plug in an audio source, can I amplify that signal and rectify it to get 0.7V? If it's possible, how would I do this? Using the TIP and GND pins? I don't have much experience with audio. I'm wondering if anyone has ever tried this or if it has been done.

[leon_heller]

Have you read the data sheet? No AVR will work on 0.7V!

[thankyou]

There is a boost converter in the 0.7V tinyAVR:
http://www.atmel.com/technologies/lowpower/default.aspx

[jremington]

The ATtiny43U is a mildly interesting chip, but it does require some specialized external components (inductor, capacitors and Schottky diode) that make it less easy to use than other AVR chips. It would be easier for a hobbyist to use one of the tiny boost converters made by Pololu, together with a regular ATtiny.

Unless you are using audio from a speaker output, there is very little power available and usually this is at very low voltage, so it would be impractical as a power source. An audio amplifier requires power, so why not just power the micro instead?

[Mee_n_Mac]

To expand on the answer above, a "line level" audio signal might go from -2V to +2V MAX and is meant to go into something like a 10k load, thus the output driver doesn't need to have much current capability. If the audio you're talking about is a speaker line, then there's potentially plenty of voltage and current (depending on how loud you turn the volume to) but most music has passages of soft and loud sound. It's hard to predict that you'll have enough power to run through the soft passages ... unless you really crank the volume.

Is the signal still supposed to be used as audio w/the MCU drawing from it or just power for the MCU ? What type of audio signal are you talking about, line level or amplifier output ?

[jremington]

Line level audio could be used to power "energy harvesting" micropower circuitry, although there may not be a good reason to do so. For example, Linear Technology's LTC3108 chip can be used to generate usable voltages from DC as little as 20 mV or AC signals of higher amplitude, which includes thermoelectric generators, tiny solar cells and piezo disks. The chip is intended to power very low duty cycle applications such as remote sensors. http://www.linear.com/product/LTC3108

[Mee_n_Mac]

The chip is intended to power very low duty cycle applications such as remote sensors.

Good point and generates another question for the OP. What's the AVR intended to do ? Is intermittent operation acceptable ?

[thankyou]

Thanks for all the responses! I have the pins of the audio jack breakout board connected directly to the pins of another audio jack that is attached to headphones. My application is very simple and so I was wondering if it's possible to take advantage of the audio signal for power. I don't want the extra weight of a battery. I was thinking that a capacitor could charge up to provide energy during the low volumes of music.
The signal is supposed to be used as audio w/the MCU drawing from it.

[jremington]

And what is that MCU supposed to do, or is this a secret?

[thankyou]

Sorry it's a secret hahaha. I'm willing to try experiments to see if I can get enough power from an audio signal, I'm just wondering where to start.

[Mee_n_Mac]

It's useful to answer the questions asked directly otherwise you'll get nothing but guesses for answers.

I might guess that you're going to rectify the signal but then think about what music is left for the headphones.

BTW the signal to a headphone set is not line level but nor is it guaranteed to be a speaker level signal. A lot of headphones amps are low power and bias the output signal on some DC level.