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I'm hooking up an LCD to my Teensy 3.2. All the connections are correct, except I had the contrast pin going to ground.

This results in the screen being filled with square blocks. If I tilt the screen I can see the text I entered is visible on the LCD so that confirms everything is working ok.

I tried to hook up a 1k potentiometer. Pin 1 to ground, pin 2 to contrast pin on the LCD and pin 3 to power. It seems that my potentiometers are dead, if I mess with the pins on the pot I get a brief display but nothing consistent.

I don't have any other pots to hand, so for the moment is there anything I can do to get a decent contrast to the display?

This is the LCD I have: https://www.amazon.co.uk/gp/product/B00ALNHTVY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Any help would be much appreciated.

Edit

I got some new potentiometers today, works fine :)

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  • 2
    \$\begingroup\$ Use resistors from 1 Ohm to 1 kOhm to get appropriate contrast. Trial and errors \$\endgroup\$ – 12Lappie Jan 23 '17 at 18:16
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In figure 2, page 7 of this document, it suggests using a 10K to 20K pot between Vcc and GND, so you might try using some 5k resistors to create a voltage divider that you can tap off of:

    Vcc
     |
    5k
     | (tap here)
    5k
     | (or here)
    5k
     | (or here)
    5k
     |
    Gnd

Try connecting the contrast input to one of the connections between the various 5k resistors and decide which gives the best result.

If you don't have 5k resistors, most any value 1k or above should work, as long as it isn't drawing too much power from your supply.

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  • \$\begingroup\$ Is it possible to break the LCD? I ask because before I connected the pot I had contrast to ground. All blocks were lit up and if I tilted the display I seen the text. I used the 1K pot, tested it and noticed the pot had faulty connections. I put the contrast back to ground to test and now I see line 1 and 3 show white blocks, the other 2 are blank. If I tilt the screen I see no text. I haven't changed any connections. Image: i.imgur.com/cUHkpH2.jpg \$\endgroup\$ – BugHunterUK Jan 23 '17 at 18:41
  • \$\begingroup\$ @BugHunterUK Since the contrast input is designed to be driven by a pot connected between Vcc and ground, applying any voltage in between should be okay. Connecting it to ground should certainly not hurt it I would start connecting the contrast input to Vcc/2, i.e. the tap between the middle resistors. If you haven't connected the display up to a micro yet, the pattern you see may just be what it initializes to. \$\endgroup\$ – tcrosley Jan 23 '17 at 20:22
  • \$\begingroup\$ FYI, in case you didn't know, the question "is it possible to break the LCD" has now been asked by the OP as a separate topic here so it's probably best to discuss that question over there, to avoid duplication. \$\endgroup\$ – SamGibson Jan 23 '17 at 22:05
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It is hard to tell what pin 1, 2 or 3 are. The pot should have one terminal to BCC, another to ground, and the wiper to your contrast pin.

Alternatively, you can use a spare mcuu pin to generate that voltage. Let me know if that's thee route you want to go down with.

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