completely new to this... pic16f690 and HD44780 message

[shelbournes]

Sorry in advance if this topic has been covered before.

I have some experience on programming pic chips ..mainly I have been using them to drive leds

My next project is to program a pic chip pic16f690 to drive the HD44780 controller.

I want to put a pre written message on the chip so that when it is powered up the screen will show the message
(the chip i have is this one) http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=290347322886

I have so far only got the screen to come on with all black squares on the first row.

Does anyone know of a simple program that I can write to the chip which contains a message...
or does someone have a .hex that I can program to it that I can test to see if it works...
I have just downloaded HI-TECH so if it is possible that I can program with that I could try that way... Please remember that I am a complete novice to this .... we all have to start somewhere

Thank you so much for your time in reading this and any help will be most gratefully received.
kind regards to you all

[Rohit de Sa]

All black squares may mean a contrast pin issue. HD44780 LCDs have a "-Vee" pin which is used to adjust the contrast. For correct display, the pin needs to have anywhere from -1.6v to +1.9v, depending on the exact driver chip used. So you may need to connect a potentiometer on the -Vee pin, and you may also be required to provide a negative supply.

According to the ebay page, you also get a diagram showing interfacing connections. Try out the circuit shown. Post it here if you still have problems.

Rohit

[shelbournes]

thanks so much for the reply
i found the pinout schematic for this lcd screen on
http://www.scribd.com/doc/6564385/4dmc?__cache_revision=1233900667&__user_id=-1&enable_docview_caching=1

it is the 4dmc-162-3

but cannot see a -vee pin listed ...sorry if i seem a bit stupid ...but i would love to get this going for a project

unfortunately the tutorials are not for this style of lcd.... have already had a word with the seller about this ...not too much help

if anyone has tried programming a message to one of these i would love to try it ...
if they have a schematic they have used this would be wonderful ....thanks again for replying

[Rohit de Sa]

-Vee corresponds to -Vo.

Look at page 14 of link you posted. It shows you how Vo needs to be connected. In all likelihood you will need to connect it like shown on the left. However, do note that LCDs which require a Vo drive like the one shown on the right (on the same page), are not uncommon.

A few steps that you can follow for troubleshooting:
-Hook up the LCD and apply power to it and the microcontroller. If the LCD starts up with black squares, then it probably is a contrast problem. This can be rectified by connecting a pot to Vo and twisting it about till the squares just disappear.

-If the LCD starts fine (ie no black squares), and only gets the black squares when you write data to it then you've probably not connected the data pins correctly.

-If the black squares appear and disappear at random, then there is a loose connection at Vo. Fix the connection; also put a 0.01uf capacitor on Vo.

I am assuming that you know what code to use, right? 4 bit mode + FlexLCD driver....

Rohit