Hey guys and gals, I have a HD44780 LCD (blue BG, white text) wired up to this picture ( http://lcdsmartie.sourceforge.net/lcd44780.gif ) but with the following changes:
- Pins 18-25 on Printer port are not grounded
- I wired 3 10ohm resistors in series to have a 3.5V reading for the LED backlight.
- I have a 330ohm resistor wired in series for the LCD giving voltage at 4.5V
Power input is coming from a 5V molex plug. The blue lights up, but I get no white text or blocks. This is the spec sheet:
http://www.crystalfontz.com/products/20 ... ATMIJP.pdf
Can you guys recommend anything or see something special about the lighting?
Our new official repo is on github
LCD Smartie version 5.6 is released!
Download it now: https://github.com/LCD-Smartie/LCDSmartie/releases
LCD Smartie version 5.6 is released!
Download it now: https://github.com/LCD-Smartie/LCDSmartie/releases
wiring my CF lcd screen
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mattcro
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I take it the power is coming from the PC's own power supply and you used a spare disk drive power connector? That should provide the ground connection to the parallel port, but it might be worth a try to connect pin 18 (and optionally pins 19-25) on the printer port to the circuit ground. At least one other person on the forum has been caught out with this.
If you're using a separate power supply, you definitely need at least one of the port ground pins (18-25) connected.
Where is the 330ohm resistor connected? In series with the LCD power supply (between 5V and LCD pin 2) or between pin 3 and ground? The 4.5V mentioned in the datasheet is the LCD (NOT the logic/controller chip) drive voltage, which controls the contrast and is set by connecting a resistor (fixed or variable) between LCD pin 3 and ground. The normal method is to connect a variable resistor as shown in the Smartie schematic you linked to. Try using the variable resistor as shown, and you'll be able to adjust the contrast to suit. It could be that in your circuit the contrast is very low and you just can't see any blocks or text.
Other than that, thoroughly check the wiring...
If you're using a separate power supply, you definitely need at least one of the port ground pins (18-25) connected.
Where is the 330ohm resistor connected? In series with the LCD power supply (between 5V and LCD pin 2) or between pin 3 and ground? The 4.5V mentioned in the datasheet is the LCD (NOT the logic/controller chip) drive voltage, which controls the contrast and is set by connecting a resistor (fixed or variable) between LCD pin 3 and ground. The normal method is to connect a variable resistor as shown in the Smartie schematic you linked to. Try using the variable resistor as shown, and you'll be able to adjust the contrast to suit. It could be that in your circuit the contrast is very low and you just can't see any blocks or text.
Other than that, thoroughly check the wiring...
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z-lite
- Posts: 3
- Joined: June 11th, 2007, 5:03 am
I have 3 5V wires. One to pin 2, one to pin 3 but with a 330 ohm resistor in series to the LCD (pin 3) and the 3 10 ohm resistors in series to the LED (pin 15). It is connected to the same PSU that everything in my computer is powered by. I will ground 18 and see if I get a different result (and 19-25 if that fails too)
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mattcro
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The +5V to pin 3 is probably the problem. Pin 3 on the LCD sets the contrast and needs to be close to 0V (ground) for good contrast. Try connecting the 330ohm resistor to ground instead of 5V and you should see dark blocks (or hopefully sensible text!) on the display.
The data sheet says 4.5V between Vdd (that's +5V) and pin 3, so pin 3 needs to be at about 0.5V above ground.
You'll have to experiment with the resistor value (or use a 10K variable resistor) to get the best contrast setting.
It's best to connect the ground to pin 18 on the parallel port, but your circuit should work without it since the signal ground connection is provided through the power supply.
The data sheet says 4.5V between Vdd (that's +5V) and pin 3, so pin 3 needs to be at about 0.5V above ground.
You'll have to experiment with the resistor value (or use a 10K variable resistor) to get the best contrast setting.
It's best to connect the ground to pin 18 on the parallel port, but your circuit should work without it since the signal ground connection is provided through the power supply.
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z-lite
- Posts: 3
- Joined: June 11th, 2007, 5:03 am
The good news is that I found the 10k pot that I ordered a few years ago from Jameco for this project (and now finally have the electrical comprehension to do it). The pot has 3 pins, do I ground one of the outer pins, wire the 5V with the 330 ohm resistor to the other end and pin 3 of the LCD to the middle pin?
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mattcro
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- Location: Scotland
That's about right! You don't really need the 330ohm resistor if you're using the pot.
I'm assuming here that the pot is the type with a shaft that you fit a control knob onto, like for a volume control.
Looking at the pot with the shaft pointing at you and the pins pointing down, the leftmost pin connects to +5V, the middle pin to the LCD pin 3, and the rightmost pin to ground.
If I've got that right, you should find that turning the knob clockwise increases the contrast. If not, swap the two outer connections. You'll probably find that most of the useable range is at the clockwise end of the pot's rotation. You can also try disconnecting the +5V from the pot - that may give you smoother control over the contrast. The best setting varies a bit between different LCDs and depends on temperature, viewing angle and the exact supply voltage.
I'm assuming here that the pot is the type with a shaft that you fit a control knob onto, like for a volume control.
Looking at the pot with the shaft pointing at you and the pins pointing down, the leftmost pin connects to +5V, the middle pin to the LCD pin 3, and the rightmost pin to ground.
If I've got that right, you should find that turning the knob clockwise increases the contrast. If not, swap the two outer connections. You'll probably find that most of the useable range is at the clockwise end of the pot's rotation. You can also try disconnecting the +5V from the pot - that may give you smoother control over the contrast. The best setting varies a bit between different LCDs and depends on temperature, viewing angle and the exact supply voltage.