LCD doesn't run on external power

Hey
I'm new here, I could use some advice on my project.

I use an Arduino Uno R3 in combination with a sainsmart 4x20 i2c LCD -> :
LCD
One needs to include LiquidCrystal_I2C.h and Wire.h for it to work.

When I upload the code and the usb plug is still connected it works fine with the "Hallo World" example,
but once I unplug the USB and plug in my 7V, 2A external supply the backlight tuns on for a few seconds, without showing anything, and then it shuts of. The LED on the back of the I2C board stays on.

I measured the voltage with usb its 4,9V while external gives me 4,95V. So this should be fine.

Any ideas? please..

Why would you deliberately use a 7V 2A AC/DC adapter when there are 5V ones on the market?

Why would you deliberately use a 7V 2A AC/DC adapter when there are 5V ones on the market?

Because he would then have to cut the end off the 5v adapter so he could connect the wires to the 5V and GND pins on the Arduino. By using a 7 v adapter he can plug it directly into the supplied connector.

Don

… once I unplug the USB and plug in my 7V, 2A external supply the backlight tuns on for a few seconds, without showing anything, and then it shuts of.

Are you sure about the supply specifications? Is it DC? Is it really 2A and not 0.2A? Is the polarity correct? Is the size correct (does it fit snugly)?

Don

floresta:
Because he would then have to cut the end off the 5v adapter so he could connect the wires to the 5V and GND pins on the Arduino. By using a 7 v adapter he can plug it directly into the supplied connector.

Don

I never had to cut off anything on my AC/DC adapters.

I buy the 5.5mm x 2.1mm or 5.5mm x 2.5mm CCTV DC power adapters on eBay. Such as http://www.ebay.com/itm/10Pcs-New-5-5mm-x-2-1mm-DIY-Female-CCTV-LED-DC-Power-Plug-Jack-Adapter-Connector-/271684143463?pt=US_Surveillance_Cables_Adapters_Connectors&hash=item3f41a30967
They have worked for the 12V and 5V AC/DC adapters that I have bought on eBay for my LED strips.

ChrisCP:
I measured the voltage with usb its 4,9V while external gives me 4,95V. So this should be fine.

floresta:
Are you sure about the supply specifications? Is it DC? Is it really 2A and not 0.2A? Is the polarity correct? Is the size correct (does it fit snugly)?
Don

He answered most of this already, but if as you say, it is 0.2A not 2A, that would do it, not enough oomph. However, if current limiting is at play, you might expect the voltage to drop below rated?

Regards,

Graham

ieee488:
I never had to cut off anything on my AC/DC adapters.

I buy the 5.5mm x 2.1mm or 5.5mm x 2.5mm CCTV DC power adapters on eBay. Such as http://www.ebay.com/itm/10Pcs-New-5-5mm-x-2-1mm-DIY-Female-CCTV-LED-DC-Power-Plug-Jack-Adapter-Connector-/271684143463?pt=US_Surveillance_Cables_Adapters_Connectors&hash=item3f41a30967
They have worked for the 12V and 5V AC/DC adapters that I have bought on eBay for my LED strips.

Which raises the question, are you plugging an external ac/dc adaptor directly into the jack socket on the Arduino board, or using one of those adaptors and feeding the 5V line directly?

Graham

ghlawrence2000:
Which raises the question, are you plugging an external ac/dc adaptor directly into the jack socket on the Arduino board, or using one of those adaptors and feeding the 5V line directly?

Graham

Feeding the 5V directly which I know is discouraged.

I never had to cut off anything on my AC/DC adapters.

I buy the 5.5mm x 2.1mm or 5.5mm x 2.5mm CCTV DC power adapters on eBay.

Feeding the 5V directly which I know is discouraged.

I'm curious about how you get that big barrel connector into the little tiny holes?

Don

Hey

Thanks for all your replies!

There are a few more components to the whole setup.
To complete this - there is one (old) 42v - 0,7A DC supply powering two stepper motor controllers and the two nema 17 motors connected to them.
One 7v-2A DC supply that powers the arduino via the external power supply input.
The LCD from my first post. One analog joystick. In general its a simple two Axis positioning System.

Everything was running fine until I tried to connect the LCD.

I found out today that the problem was the 42V supply. It was positioned too close to the Arduino. Even with 15 cm distance between them the LCD did not work at all. The signals got jammed up because of the electrical field around the 42V supply.

The two DC supplies were connected to the same 230v AC line so when switching them on at once I got the impression the external power for the arduino was the cause of the Problem.

I think since all the other signals are digital this had no effect on them. - steppers were doing fine.

If anybody ever comes across a problem like this, check the electromagnetism. (you can see very fine moving lines on the LCD) The Arduino seems to be sensitive to it when it comes to I2C signals.

Hope I could explain this well enough english is not my native language :wink:

Thanks again!

floresta:
I’m curious about how you get that big barrel connector into the little tiny holes?

Don

AC/DC adapter  <--> 5.5mm x 2.1mm or 5.5mm x 2.5mm adapters <--> Arduino
                                                            <--> 5m LED strip

I'm not really that ignorant. I was just trying to answer your question.

As you finally have admitted, there's more to it than just using a 5 volt adapter in place of a 7 volt adapter.

Don

floresta:
I’m not really that ignorant. I was just trying to answer your question.

As you finally have admitted, there’s more to it than just using a 5 volt adapter in place of a 7 volt adapter.

Don

I never said that you were ignorant. Your own insecurities brought that thought about in your head.

I merely was explaining what I did. If using a 5.5mm x 2.5mm adapter as a convenience item is “more to it” then I guess there is “more to it”. I prefer not to cut and solder wires if I didn’t have to. My project required 5V for the LED strips. The Arduino can run on 5V.
2 birds with 1 stone.