Tom Lewis wrote:
I also bought a £1.66 LCD Moduel display, because it was dirt cheap and uses "HD44780" which I saw some tutorials used, alas it is 5V.. Ebay Link
I would love for this to be my first project, getting this LCD to display some text, Is it possible with the kit that I bought? I have read online that its dangerous playing with anything that isn't 3.3 volts as it could fry the pi, I haven't got a clue where to start!
LCD's such as this work perfectly when the control signals are 3.3Volt, in fact just 2.0 Volt is enough.
With LCD's as this its possible to read the contents of the LCD registers, which potentially would put 5V on the data lines, but its possible to wire the LCD up so that you can only write to the registers.
If you are still afraid you make a mistake simply wire 1K resistors in series with all the wires going to R-PI GPIO's! This would largely protect the Raspberry PI from putting 5V on its inputs.
It would mean the current flowing from the 5V source into the GPIO's would be limited to 5V - 3.3 V = 1.7 Volt which divided by 1K give a current flow of 1.7 mA. So in worst case just 1.7 mA will flow into the GPIO's through the protection diode inside the GPIO port logic to the SoC's 3V3 supply.
Because the LCD's inputs have a very high input resistance 1K resistors do not diminish the voltage level reaching the LCD.
normally a power on reset capacitor is connected to ground, is pulled up to VCC, but with these kinds of LCD's a strange trick is used to make them compatible with two fundamentally different 8-bit microprocessor busses, one as used by microprocessors like the intel 8085 and z80, and the other like 6809 and 6502. When controlling the LCD it doesn't matter which one you pick, but it matters for the software, so you have to be aware which one you use.
Normally the LCD is controlled by writing bytes into an 8-bit register, but when you have a limited number of control lines, you can switch the LCD to "nibble mode". Only control the upper 4 bits, and tie the lower 4-bits to ground. Then send a "magic sequence" to the LCD which will switch the LCD to nibble mode.
Details are in the LCD's datasheet.
Also remember to add a resistor divider, or potentiometer for the LCD contrast, and a series resistor for the backlight LED's.
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