LCD module - PC Parallel port

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I am using HD44780 based 2x16 character LCD Module. (Model : CCS1620CSL) I
am using it in 8-bit, 2line mode.





I've wired up  the LCD module to the Parallel Port of PC as shown here :
http://www.codeproject.com/csharp/cspplcds.asp



Nothing appearing on LCD except 16 black boxes. No effect of init routine.



Signals on Parallel port is working fine. I've checked them using
multimeter.Still there is no activity on the display except 16 black box.



One thing is - signals on parallel port are as follows:

2.48 V for Logic 0

5.5 V for Logic 1



Can this be a problem? Any ideas???



Thanks and Regards,

-Neo





Re: LCD module - PC Parallel port
Hi Neo,

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should be less then about 0,5V. You must have a short circuit
somewhere...or your port is defective. Check your wiring.

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Thats good.

HTH
Wolfgang

--
From-address is Spam trap
Use: wolfgang (dot) mahringer (at) sbg (dot) at


Re: LCD module - PC Parallel port
I checked connecting it to another machine. Output voltages are the
same.

O'kay, How can I make the voltage 2.48 -> 0 (for Logic Low) and 5.5 ->
5 (for Logic High)? So, that it comes in the acceptable range of
HD44780 LCD module?

Thanks,
-Neo


Re: LCD module - PC Parallel port
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By connecting the ground ?

Meindert



Re: LCD module - PC Parallel port
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I don't know if the parallel port wired correctly, but the resistor
on pin 3 of the LCD should be a 10k pot, wired between +5 and GND
and the center of the pot to pin 3 of the LCD. Right now you have a
fixed contrast and you want it variable.
rw

Re: LCD module - PC Parallel port


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rw is right,
             and this could be a contender for the '16-black boxes', the
contrast is too high. Have you used the circuit with the pot (incorrectly
wired in the diagram as rw has already mentioned), or the circuit without
the pot. My recommendation...you need the pot (not all LCDs behave the same
in my experience).

Also, how did you measure the 0V level?. Did you measure it when the PC was
attempting to write to the display? or did you measure it when the PC was
idle?. If you have a scope it would be better to capture a data burst and go
from there.

Don't shoot me down, but you did measure the data port signal with respect
to your parallel port 0V and you have connected the parallel port 0V to your
5V supplys 0V? It doesn't show this connection on the schematic. If you are
using an isolated 5V supply (a battery?), then you do need to connect the
parallel port 0V to your 5V supply 0V line.

Jim
www.picmodules.com




Re: LCD module - PC Parallel port
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hi, which pin is the ground on the PC-printer port?
That schematic shows nothing.
rw

Re: LCD module - PC Parallel port
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got the answer:
any of the Green pins (G18, G19, etc)on the printer port is GND. So pick
one of those to connetec to the power supply GND to and you have the
proper reference.
rw
to your input levels.

Re: LCD module - PC Parallel port
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The problem was solved when I connected parallel port GND to +5V power
supply GND.

Now, It's rocking!!!

Thanks a lot to all of you.



Just to understand - why this was a problem, I thought GND is always the
same whether it is from parallel port or from the power supply. Isn't it the
potential difference, and that should be the same in either case?



I really appreciate and thanks to all who shared their ideas and help me
make it rocking :-)



Cheers,

-Neo



Re: LCD module - PC Parallel port
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when you add a power supply to a system (your pc) they must have a
common reference point (GND)
rw

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