problem with Nokia Color LCD

confini · Joined: 29 May 2006 Posts: 6 Location: Italy

Hi everybody!
I am experiencing a strange behaviour with a Nokia 6100 color LCD:
I am using the code as in this example from the CCS code library, with the difference of having a 18LF4520 instead of a 18F4620, a 20Mhz clock for the PIC and that we use MCLR pin for reset.

The strange thing is that the LCD works correctly, but this morning after removing power from my lab PSU, and attaching batteries to the system (my system is powered by 2 AA batteries, with a stepup for having system VCC at 3.3V) the lcd went off, like dead (displaying full blue).
Of course reconnecting the PCBs to the lab PSU didn't give any result... still blue!

I checked the connections between my main PCB and the LCD PCB, where there is the circuit for obtaining the 6.8V for the LCD led) and they are OK. Also power is OK, measuring constant 3.3V as VCC, also to the LCD and constant 6.8-6.9V at the LCD led contact.

So the HW seems OK, I think problem is in SW. But what ?

any help would be GREATLY appreciated, all the best,

Nicola

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

1. When you connected the battery-powered DC-to-DC converter
to your PIC and LCD, did you accidently reverse the polarity ?
If so, some devices were probably damaged (such as the LCD)
or the flash program in the PIC may have been partially erased.

2. When your circuit was running from the lab power supply, what
voltage were you using ? Was it +3.3v, or was it +5v ?
I ask this question, because if you have Brownout reset enabled,
and the Brownout voltage is set for +4.2v, when you switch to
a Vdd of +3.3v, then your PIC will be always be held in reset.
It won't run.

3. When you use the lab PSU, does your PIC do anything ?
The LCD appears dead, but what about the PIC ?

amcfall · Joined: 20 Oct 2005 Posts: 44

If you have spare hardware I'd give that a shot, I've had great luck with my screens. I bought three figuring I'd blow a few up but no smoke so far.

What connections does yours have? The little .5mm pitch surface mount connector came loose on one of my hand soldered boards and I had to rework it.

Avery

confini · Joined: 29 May 2006 Posts: 6 Location: Italy

Hi,
thanks for your posts, here is my answer to you:
1) I have and hardwired connection, so I didn't invert the polarity
2) I was running my circuit with my lab PSU set at 2.4V (same as the 2 AA batteries in series)
3) with the lab psu attached the whole circuit (PIC + LCD + all the other devices connected to the pic) works good. Even with batteries all is fine, except the LCD! This is why I am going crazy!

for the connections I use this connector:

http://www.sparkfun.com/commerce/product_info.php?products_id=570

to connect the LCD to its PCB, and a flat cable from the LCD pcb to the main pcb.

What I don't really understand is that sometimes works, sometimes not... if it wasn't working at all, I could think of an HW problem, but this "work/not work" leaves me really without any idea.
I've also changed the LCDs (I have 3 of them) and the situation didn't change at all...

amcfall · Joined: 20 Oct 2005 Posts: 44

What pic does 20Mhz at 2.4V? I sure could use one.

Do you have another adapter board with fine pitch connector? Intermittent connections can be a pain to debug.

Avery

confini · Joined: 29 May 2006 Posts: 6 Location: Italy

Hi,

>
> What pic does 20Mhz at 2.4V? I sure could use one.
>

I don't know this. My pic is 3.3V powered at 20 Mhz, I get 3.3V as output from a stepup which gets 2.4V as input.

Anyway I have another board, tested and it has the same behaviour.
I think I am going to cutoff the connector and use cables directly soldered to the LCD itself...

thanks again,

Cirutech

amcfall · Joined: 20 Oct 2005 Posts: 44

Which LCD do you have? The one with the brown cable from Sparkfun? That is the one I have tested with. I have also not etsted over 8Mhz, though the display should work IIRC. Haven';t looked at the Epson data sheet recently.

Also, if the LF4520 is like the LF4620 20Mhz is too fast at 3.3V, I think the max is around 9Mhz.

Avery

confini · Joined: 29 May 2006 Posts: 6 Location: Italy

Hi,
and thanks for your answers.
Yes, I am using brown-cableld LCDs from Sparkfun.
About the clock speed, I think that the 20Mhz clock is ok, owing to the fact that the rest of my circuit works properly, and also according to this post the use of a 20Mhz crystal for a PIC18LF @ 3.3V should be ok.

all the best,

Cirutech