LED lights up using USB-power but not using +8V DC from power jack??


I have built dB-meter that will also light up a VU-meter depending on the incoming sound to the microphone.

Everything works just fine when using USB for power the whole circuit (including Arduino, Network shield, OP-amps and the microphone). But when using the power jack that has been designed to deliver +8V DC, the VU-meter dosen't work, even with the same code. The microphone still function correctly and records audio and save it on a SD-card (have been observed). The VU-meter uses RGB-leds that lights up at a 0 output from a pin and the Anod is connected to 5V. The VU-meter RGB's are connected to different output pins.

All components in the circuit uses the GND on the Arduino UNO for grounding. The entire circuit should therefore have the same GND.

The circuit also works fine if both the USB and power jack are connected but as soon as the USB cable is removed the VU-meter dosen't work.

Any ideas?


But when using the power jack that has been designed to deliver +8V DC,

What? The power jack delivers nothing it takes in a voltage.

What is the current rating of your external power supply?

Sorry my bad!

230 V AC down to 9 V AC 500mA. Then I have designed a voltage regulator after that adapter with diodes and capacitors, to make a delivery of +14V and -14v DC to power the OP-amps, and then I use a LM7808 to make a stable +8V DC for powering the Arduino via the power jack.

It looks like your power circuit can not provide the current. Have you got the capacitors in the right place to stop it oscillating? Cair to post a schematic of this power supply.

Of course!

Here comes the schematic of the power supply. The +8V is used to power the arduino through the power jack and also power the electret microphone with +3V through a voltage divider. The ±14 V are used to power the OP-amps.

Power supply.png

The schematic has a LM7809 but in the real circuit it is a LM7808!!

Thanks, that looks OK so the only thing is that transformer. Have you checked the output voltage under load?