Hello everyone,
Before starting with my issue I would like to tell you that this is my first arduino project and that I'm generally just a hobbyist with limited knowledge.
I am trying to use an LCD display that I have purchased from eBay (link) but I cannot make it show anything.
Another issue is that I can not control the contrast from pin3.
I have searched in this forum and the only info I found is that if I connect pins 1,2,3,15,16 I should at least see some blocks, but I cant see anything.
I have uploaded a couple of pictures on my DropBox (couldn't attach here due to big size)
DropBox Pictures
Am I doing anything wrong?
Is it possible to fix it?
Ps. I couldn't find any datasheet that I would be 100% sure that it's for my LCD
You have connected A, K to 5V, 0V. So I would expect the Blue backlight to shine.
I would be happier with a small resistor e.g. 47R. You can see that R8 is 100R from your photo.
Obviously you need to connect RS, EN, RD, D4, D5, D6, D7 for it to display any text.
If you own a DMM, you could check whether A, K are reversed.
The displays may be cheap for a reason. OTOH, there would be a lot of bad feedback.
David.
I finally found a solution.
Even though EVERY tutorial on the Internet says that you need to connect the contrast pot to 5v, for some reason, the pin3 is powered internally for this specific LCD, so all I had to do, was to not connect the pot to 5v.
See attached picture.
P.S. thank you david_prentice, I saw your comment after I have found the solution.
You don't actually need to connect data pins to see if contrast works. As for for A and K pins, they control the brightness, not the contrast. But thank you anyway
The VO pin needs to be about 0.4V on most 5V displays.
Many have a 10k pullup on the pcb. So all you need is a resistor 0R .. 470R between V) and GND to produce the contrast voltage.
Your pot is providing a "variable resistor" if you have disconnected one end terminal of the pot.
Measure the successful resistance. I bet that it will be between 0R and 500R.
Bill Perry will probably know whether panels exist without the pullup. Obviously those displays need to have a pot instead of a single resistance.
David.
Even though EVERY tutorial on the Internet says that you need to connect the contrast pot to 5v, for some reason, the pin3 is powered internally for this specific LCD, so all I had to do, was to not connect the pot to 5v.
It should have worked either way.
Bill Perry will probably know whether panels exist without the pullup. Obviously those displays need to have a pot instead of a single resistance.
I haven't run into any.
If the manufacturer of the board has followed the "Drive Voltage Supply Example" shown in Figure 21 of the HD44780 data sheet then the 'pullup' function is provided by a ladder network of four or five resistors providing the various voltages needed by the display.
NOTE that that above mentioned figure shows the lower end of the variable resistor going to -5V which is required for extended temperature range displays. It can be (and normally is) connected to GND for standard temperature range displays.
Don
