The only major drawback with this LCD module it requires a -ve Bias Operating voltage (Vo = pin3) for a visible display.
There are two ways around this:
1)use a dual supply
Or
2) Use a -ve pump charge circuit, driven by a spare pin of microcontroller. So a single 5V supply is all that's required
This article is covering option 2.
First is the hardware:
Components are very cheap and readily available are:
1) 1N4148 signal diode 2 off
2) 22 uF 2 off. Voltage is not critical e.g 25V is OK.
3) 10K Trimmer.
Third item is not an additional expense, since this is required anyway to alter contrast.
- Neg drive LCD.JPG (15.15 KiB) Viewed 4613 times
I decided that a waveform frequency driving the circuitry could be about 1 - 2 KHz .
With equal on/off that means required interrupt frequency should be double.
Using Timer 2 set at 3.9KHz (since timer 1) is used for something else.
I have just got a spare pin to toggle every time interrupt is accessed. That way a frequency with a duty of 50% is produced.
Conclusion.
Using this method appears to work out cheaper than paying out for a display that requires a bias between 0 and +5V
Adjusted so o/p was at -0.5V with respect to ground, and display text was crystal clear.
Note: Display is connected to port A. Pin that is used to drive charge pump is A6
Target oscillator frequency is 4MHz
So you will need to adjust those settings for your device and frequency.
Flowchart was created using Flowcode V4.
If you try this out please let me know how you get on.
Thank you.