Testing a HD44780 driven LCD

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barrystyle

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Hi all,

First post here.

I am looking to test a HD44780-based LCD screen, which is currently connected to another circuit.

From what i've seen, 5v to Vcc and normal ground isn't enough to get the LCD to light up. I have tried directly powering the backlight, this also does not work. Will the LCD display anything at all without the backlight?

Are there any easy resistance checks etc I can do to make sure the LCD is working?

I am not sure if the circuit which provides it with data is working either, so I am trying to cross out possibilities here.

Thanks for any replies,
james
 
You simply need to connect the power the the module, and a contrast control - by adjusting the contrast you should be able to see a single row of black rectangles.

Obviously this is only a VERY limited test, but it proves it's not dead - and is what you get if the program isn't initilising the LCD correctly.
 
i dont have any pots available, what resistance do you recommend to get any display at all?
also, do i just go from the contrast pin to ground?

(sorry am still learning)
 
barrystyle said:
i dont have any pots available, what resistance do you recommend to get any display at all?
also, do i just go from the contrast pin to ground?

(sorry am still learning)
Click to expand...

You need a pot - slider to contrast pin, ends to +ve and chassis.
 
i cant actually identify which pin is the 'contrast' pin on the controller, does it have a shortened name?

im also confused about the pot pinout, are you able to show me a diagram with what you mean?
 
barrystyle said:
i cant actually identify which pin is the 'contrast' pin on the controller, does it have a shortened name?

im also confused about the pot pinout, are you able to show me a diagram with what you mean?
Click to expand...

Check my PIC tutorials, the LCD hardware one shows how it conects.
 
barrystyle said:
i dont have any pots available, what resistance do you recommend to get any display at all?
also, do i just go from the contrast pin to ground?

(sorry am still learning)
Click to expand...
You can try a 1kΩ (or in proximity) resistor from the contrast pin to ground. Using a pot allows for changes in temperature, and different makes of displays.
 
I've found a pot is essential. Even on the same model LCD from the same supplier, there are enough differences that the contrast setting the works for one doesn't result in seeing anything on the other.
 
hi all,

have hooked up with a 10k potentiometer, yet i cant get any display at all.
ive tested to make sure the powersupply is putting out 5v min under load.
ive tested the connections from the HD44780 board pins to the potentiometer outputs (i soldered onto the data board), there is no resistance.
so i just assume i have a dead lcd and move on?

**broken link removed**
 
It looks like you have it connected to a circuit?, you may not be able to test it in this way if it's not fully disconnected.
 
just isolated the lcd from the data board, still doesnt work.
noticing the 5v and gnd are swapped in lots of generic lcd pinouts ive seen, i then tried swapping them around and the HD44780 went past 60 degrees celcius so ive most likely cooked it...
 
barrystyle said:
just isolated the lcd from the data board, still doesnt work.
noticing the 5v and gnd are swapped in lots of generic lcd pinouts ive seen, i then tried swapping them around and the HD44780 went past 60 degrees celcius so ive most likely cooked it...
Click to expand...

If you'd got it powered the right way round, the contrast pot connected correctly, and you couldn't get any display by adjusting the pot - then it was probably faulty anyway.
 
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