I've got a queston to the Arduino UNO R3 when using a display which is HD44780 conpatible.
My circuit:
Arduino UNO R3 on which there is an ethernet shield and a RFID-Shield by SparkFun (13.56 MHz, Module SM130).
I attached the circuit which doesn't contain the RFID-Shield because I couldn't find a component for Fritzing and the code.
My problem:
I want to connect the display which supports 5V to the RFID-Shield. This even works but the display is hardly readable.
My retailer told me that I should include a 110 Ohn resistor (which I didn't include into the circuit attached) into the GND-line to increase the brightness.
But (as I expected it) the display got even darker instead of brighter. So I thought I could connect the Arduino to an external power supply (5V, 1500mA).
But even that didn't bring any success. So have you got any idea how I could increase the display brightness?
I've got another question: If the Arduino is not connected to USB but only to an external power supply the display (and the RFID-Shield) don't work.
What can I do to solve this problem?
You should have a variable resistor between pin 3 and GND. This sets the contrast of the display. Adjust it until the display is to your liking. A typical value variable resistor to use is 10K?.
thank you for your very fast reply. But what do you mean by a variable resistor? And do you mean the 3rd connector on the display or the digital pin D3 by "pin 3"?
Do you mean I should use a potentiometer? But potentiometers (at least all that I've seen so far) have three connectors. So how do I have to connect the resistor?
I mean the third pin of the display (your light blue wire), and a variable resistor is two pins (middle and one end) of a potentiometer.
Also, it looks like you have no proper ground connection - pin 1 of the display should be connected to ground; I see nothing connected there at all.
Pinout:
1: Ground
2: VCC (+3.3 to +5V)
3: Contrast adjustment (VO)
4: Register Select (RS). RS=0: Command, RS=1: Data
5: Read/Write (R/W). R/W=0: Write, R/W=1: Read
6: Clock (Enable). Falling edge triggered
7: Bit 0 (Not used in 4-bit operation)
8: Bit 1 (Not used in 4-bit operation)
9: Bit 2 (Not used in 4-bit operation)
10: Bit 3 (Not used in 4-bit operation)
11: Bit 4
12: Bit 5
13: Bit 6
14: Bit 7
15: Backlight Anode (+)
16: Backlight Cathode (-)
in my case these two cables are not connected at all. So do those pins enable the backlight? Where do I have to plug them in?
Also, it looks like you have no proper ground connection - pin 1 of the display should be connected to ground; I see nothing connected there at all.
But the display works. In my opinion it wouldn't work at all if there was no connection to ground. So what about that problem?
I said no proper connection to ground. There will be a connection via other routes, but that connection won't be direct to ground, but via other components. If there is a ground pin you HAVE to connect it to ground - it's there for a reason. USE IT. Yes, it will "work" without it, but not for long and not very well.
If the display has a backlight (some do, some don't - the ones that don't still often have the connections as it's a standard board) then connect the - to GND, and the + to +5v. It might need a resistor in there too (it's just LEDs), depending on if there is one there already or not (again, some do and some don't). The data sheet for your specific display should tell you.
