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tonyhughes
Posts: 951
Joined: Wed Dec 26, 2012 3:46 am

LCD display on really long wires

Thu Feb 14, 2013 10:23 pm

I would like to put a small two-line LCD display screen in the hallway by the front door, so as we come home, at eye level, we can see number of new emails, new voicemails, how many times the door bell has been rung, how many missed calls we have etc etc.

I can do all those tasks, but can I use super long cables from GPIO pins to a display (i.e. 20 meters?).

If not, what would be the preferred way.

I would rather use an existing Pi that lives in the office, than redeploy a Pi into the hallway.

pgman
Posts: 22
Joined: Sun Jan 06, 2013 8:34 pm

Re: LCD display on really long wires

Sat Feb 16, 2013 1:38 am

Wouldn't advise trying to directly connect to an LCD over more than about 50cm. What you are best off doing is using a serial to parallel converter chip and connecting that chip direct to the LCD.

Have a look at this blog http://www.rpiblog.com/2012/07/interfac ... ry-pi.html
It explains how to connect a Pi to a PCF8574 I2C serial to parallel chip and then in turn to an LCD. If you are OK building your own then there is a circuit diagram included. If your not into circuits then you can either buy a board with the chip on it (ebay search for "i2c lcd 1602") or buy a serial LCD board from someone like sparkfun or even ebay.

There is a driver library call LCDproc that handles all kinds of connections to LCDs, including PCF8574 chips.

The other thing to be aware of is that most displays and driver boards are 5v, and the Pi GPIOs are 3.3v, so its important to make sure that none of the pins going to the Pi GPIO pins are carrying 5v. If you make the circuit yourself this is easy, as you just make sure there are no pull-up resistors to 5v on the I2C busses of the chip, (the necessary pull-ups are already on the Pi). If you are in any doubt though, then connect a level shifter between the Pi and the chip - again search ebay.

I should point out that I've not tried using this with the Pi, this info comes from my Arduino experiences.

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