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Topic: SOLUTION: To poor contrast using a POWERTIP PC1602LRU-HWB High temperature LCD (Read 2 times) previous topic - next topic

insanityideas

This particular LCD is a special high temperature version of the standard powertip LCD display (as indicated by the H suffix). It is designed to work at temperatures between 20-70c, which means if you wire it up following the "hello world" examples it won't appear to work (blank display) because the contrast is so poor due to the low temperature. This solution will probably work with other LCD displays showing a similar issue, but no promises.

This post is to help people out who have suffered this problem and don't know the solution, I originally found the fix on this read-only part of the forum, however the solution was a bit clunky so I wanted to post a better way.

To make the contrast higher you have to draw the contrast pin to a voltage lower than the ground voltage that the board uses. Normally you would do this using a power supply that has multiple rails, or some other multi component solution, but there is a quick fix that is good enough for most situations.

Connect up your circuit as normal, tying all components to a common ground. But rather than connecting this directly to the negative end of your power supply... connect it through a diode, and then connect the LCD contrast pin to the negative power supply end of the diode. Because a normal diode has a 0.8v voltage drop across it you have now created a voltage divider that will hold the LCD contrast pin 0.8volts lower than the ground for the rest of the circuit. Make sure the diode is sized to handle the total power requirements of your entire circuit and is connected with the silver stripe closest to the negative lead of the power supply.

This 0.8volt difference seems to set the contrast just right, but if you need it darker add another diode in series.

In some cases this extra voltage divider might cause issues as the circuit ground is floating 0.8volts above the power supply ground, which could affect measurements taken by the arduino that are relative to the power supply ground.

pefo

Hi, try to generate negative voltage from PWM pin ... http://www.piclist.com/tecHREF/microchip/pwmvee.htm

or use 555 to create negative voltage.

555 volatge inentor works fine - tested.  - link: http://www.electronicecircuits.com/electronic-circuits/555-negative-voltage-power-supply-circuit

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