Problem with 9V power supply to Arduino Uno, MP3 shield, servo motor, LM386 amp.

Other Hardware General Electronics
1

Hi,

I'm making some little music, beat boxes with kinetic graphics on the front triggered from a GP2Y0A21YK general purpose type close proximity sensor. Everything's working fine except for the power supply. I've had everything running with a 9V battery to the audio amplifier and a 9V ac adaptor for the Arduino Uno, MP3 shield and servo motor but I want to take the battery out of the equation so I've daisy chained the power to the LM386 audio amplifier (kit) onto the 9V ac adaptor. Now as soon as I turn it on I get a high frequency drone and the audio is distorted. The servo runs, no problem and I've disconnected it to see if it's pulling too much power but the distorted audio is still there without the servo running. Any ideas on how I can power this up from the one 9V ac adaptor, the one I'm using is from Sparkfun, which I got in Australia from littlebirdelectronics. Thank you in advance for any solutions to this ...

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2

Is the 9V supply regulated? Is has to be regulated for an audio amplifier.

3

Are all the grounds connected together? Have you measured the voltage to see if it's really 9V?

4

Thanks, all the grounds are connected and it is 9V but I'm not sure how to check if it's regulated and also exactly what that means?

5

Remove all load from it and see if it's still 9V.

6

Ok, will do ...

7

What frequency band is this "high frequency drone" like?
You should be able to tell without instrumentation whether it sounds like

repetition rate fundamental

1 to 5 kHz
5 to 10 kHz
off the scale

is that constant or does it depend on things?

main harmonic content

purish sinewave
square wave
pulse train
other

is that steady or does it depend on things?
for example, if it sounds like a pulse train, and 200 ohms from arduino +5 to arduino GND makes it louder / fatter pulses then you'd diagnose arduino pwm draw is a possible noise source and decouple with one or more big capacitors for power supply of each of the audio and arduino circuits, separated by 5 Ohms. That might do the trick.

Answering the description of the sound would help with both choosing the right decoupling capacitor and identifying the root cause of anything bad going on.

8

Thanks for the sonic detail. I'm re-wiring on the weekend (that might also be an issue) and will check the frequency response and get back with more detail. Thanks again, much appreciated ...

9

This is a kit, you built it yourself?

Might be worth posting some close up shots of your circuit board, you may have a diode or capacitor backwards or something silly, if you got the polarity wrong, you'd have seen more of a smokey effect floating up in the air, with a burning smell..

This is where a cheap 555 timer circuit comes in handy, you can create a probe which simply sends out little beeps then you can share the ground and poke and prod the amplifier to see at which stage the amplifier fails.

10

I think it's a 5 to 10 kHz, pulse train and both are pretty steady, but I've only kept the connection going for 10 secs or so …

11

Yep, it's the K102: LM386 Audio Amplifier kit from http://www.circuitcreations.com/Circuit_Creations_Kits.html

I put it together and checked it with other input/output sources and it works fine, so I'm hoping the amp, as I've built it, is not the problem. I'll go back and have a look, see if everything is polarized correctly and thank you for the tip ...