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Potentiometer causes(?) gibberish on LCD

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  • Potentiometer causes(?) gibberish on LCD

    I have a 2x20 (4-bit) Seiko hd44780 lcd which I am planning to mount in the car as soon as I got the contrast straightened out.

    WHen I have the contrast pin wired to gnd, the screen shows nothing. When it's wired to +5 it's readable but very dark.

    Now that I have the pot wired in, it still works if I have it turned up to 5V, but if turn it down to a comfortable viewing contrast (3.8V) the screen soon starts showing a storm of gibberish. In some cases, it returns briefly to showing proper output and in other cases the screen goes blank.

    I've tried wiring the pot in both 'directions':
    (1,2,3)=(+5,Cntr,gnd) & (1,2,3)=(gnd,cntr,+5)
    ... but it shows the same behavior either way

    What's going on?

    The pot: (It's the 63X-103)