Dim LCD

Projects General Guidance
1

The subject pretty much says it all. Can an Arduino power a standard 16x2 LCD and a series 2 XBee at the same time?

If not, could either be powered by a 3xAA battery pack? (Which would combined output 4.5v)

Note that the XBee uses the XBee Explorer Regulated from Sparkfun - it takes a 5v input and I assume it brings that voltage down to 3.3v for the XBee. So the batteries shouldn't undervolt it or something. But can a standard 16x2 LCD take 4.5v power instead of 5v?

Thanks!

2

Yes, an arduino can power an LCD plus an Xbee. Now, what do you to use to power the arduino? :wink:

3

The standard input voltage for an arduino is 7V-12V if you're using external source.
I used a 9V external battery to run tests with my arduino and zigbee and the battery dries up within 2 days.
Not a very good idea to use batteries.

4

liudr:
Yes, an arduino can power an LCD plus an Xbee. Now, what do you to use to power the arduino? :wink:

9v.

The exact problem I'm having is - when I turn on the Arduino, the LCD is very dim and the backlight doesn't turn on. Originally I assumed the XBee was the root of the problem, as this showed up when I attached the XBee. I don't think that's the case anymore, as I snipped the +5v wire going to the XBee and the LCDs still dim.

One other thing - it's going through an I2C expander with the library here as well as an IDE cable. It worked fine before.

Well, I'm off to go check my soldering for errors for the umpteenth time. Thanks guys!

EDIT: Oh - the logic works just fine. It prints what it's supposed to print. Thought I should mention that.

5

You need to understand the difference between Power, Voltage, and Current. (You are only focused on Voltage.)

Power is the product of Voltage and Current. Voltage is pressure. Current is flow.

Since current is flow, you need to determine how much current each device is going to consume and how much current your source can provide. Look at the spec sheets for each of the components you are using to determine how much current they are going to consume (or draw.)

I used a 9V external battery to run tests with my arduino

9V batteries are an ABSOLUTELY LOUSEY source of current. You are FAR better off using a AAs than a 9V.

6

Thanks for letting me know.

Although I plug it in through USB and it does the same thing.

7

I have several projects with LCD and other stuff running on 9V battery. The 9V battery is week in power so if you want to draw more than 100ma or so current the voltage drops from 9V quite a lot. I suspect the LCD back light is consuming too much power. Do you have a current limiting resistor on the lcd back light?

8

liudr:
I have several projects with LCD and other stuff running on 9V battery. The 9V battery is week in power so if you want to draw more than 100ma or so current the voltage drops from 9V quite a lot. I suspect the LCD back light is consuming too much power. Do you have a current limiting resistor on the lcd back light?

No, it shouldn't need one, though. I assume that it's baked into the thing. Again, it's worked in the past.

I threw 6 AAs in a battery pack and plugged it into the Arduino. No dice. The LCD is still dim.

Is it possible I somehow fried the LCD?

9

I figured out the problem. On one of the pins on the LCD's 16 pin header, the solder had broken. I resoldered that, and it works just fine.

Thanks all!