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Support Forum » 30 V DC Adapter

August 20, 2011
by plehrer
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Hi, I soldered my positive and ground wire to the plug that connects to the DC Adapter that comes with the LED Array Kit. In the LED Array Kit project PDF it says that the adapter for the kit outputs 9 Volts. However, I checked for voltage with a Multimeter and it read 30 V. Also, in the documentation it said that the 7805 voltage regulator can handle 7 V to 30 V. So, I hooked it up to my original Nerdkits with the temperature sensor program running and all I got were two lines of "###" in the LCD. I checked that the kit was in run mode and not in programming mode. Also, when I ran the project with the USB cable as the source of power, it works just fine.

Below is a link to a picture of the wires soldered to the plug for the adapter. I believe that I did get the correct wires soldered to the correct joints. Also, when I used the multimeter it read 30 V only when the green wire (ground) of the plug was connected to the black wire of the multimeter and the red wire (positive) of the plug connected to the red wire of the multimeter.

Should I not expect the DC adapter to work with the original Nerdkits because it outputs too many volts?

Red and Green (positive and ground) soldered to the DC Adapter plug

August 22, 2011
by hevans
(NerdKits Staff)

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Hi plehrer,

The power brick is an unregulated power supply, which means it is rated to output a certain voltage at a certain current. In this case I believe it is 9V at 300mA. When you measure it unloaded, the reading doesn't really mean much since your multimeter is drawing practically no current from it. Your picture is a little fuzzy for me to be able to tell if you got the connection right, but you can double check with your multimeter. Make sure whichever lead is positive relative to the other one goes into the input of the 7805, and the other lead goes to ground. Measure the voltage between the output of the 7805 and ground, is that 5V. Then measure the voltage from the input of the 7805 to GND, that is the output of the wall wart which when the MCU is turned on should be in the more sane 9-12V range. Let me know what you find.

Humberto

August 22, 2011
by plehrer
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I measured the voltage as you suggested from the input of the 7805 to GND on the temperature sensor kit and it showed 14 V with the multimeter set at 200 on the orange part of the dial. (I hope this setting is correct.) The LCD with the temp sensor still doesn't work when powered by the power brick. However it works fine when powered by the USB to serial cable.

The power brick does in fact work with the LED Array kit so I know the wires are connected to the right leads from the plug. The voltage on the LED array kit from the input of the 7805 to GND fluctuates from 12 V to 13 V, again with the multimeter set to the 200 on the orange orange part of the dial.

I hope I did this correctly.

Thank you for your help, Peter

August 23, 2011
by hevans
(NerdKits Staff)

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Hi Peter,

What you are measuring seems reasonable. Did you measure the output of the 7805 to GND, is that a good clean 5V?

Humberto

August 23, 2011
by plehrer
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Yes, output is a clean 5 V from the output of the 7805 to GND when using the adapter on both the temp sensor kit with the LCD and the LED array kit. Would an adapter with a lower power output do the trick? It would be nice to have a wall adapter power it instead of my computer.

August 24, 2011
by hevans
(NerdKits Staff)

hevans's Avatar

Hi plehrer,

You actually have me pretty confused right now. Given the numbers you have measured there is no good reason why your adapter should not be working. Could you perhaps post a good close up picture of your entire setup (with the power adapter connected), perhaps there is something wonky that I'm not thinking of. Is the 7805 getting hot at all when you connect the power adapter?

Out of curiosity, can you remove the programming switch entirely from your board, this will prevent your chip from booting into programming mode, and then connect your power adapter. See what happens.

Humberto

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