LCD Madness

[jimi252]

Hello, and sorry to bother you guys! but before i shake hands with all 3phases at work, maybe somebody can help me here.
I have a PIC, its a 16F877...and i have this 2x16 character LCD, which i think is a standard hitachi 44780 LCD. I think both the LCD and the PIC are working fine..seperately that is... when the LCD is connected to power supply, i see the first line is filled...nice...now the problem is that when i connect the display to the PIC... the display doesn't get initialized. nothing happens.. and the PIC dies..and it wont start/restart unless i disconnect the wires goin to the LCD
I tried tons of codes.. this has nothing to do with code.. i tried all ports and all configurations 4/8 bits... I'm sure i got the GND/VCC/contrast wires connected to the right pins since it shows the first line and the contrast thing works.. so i guess all the other pins follow in the standard manner RS/RW/E/D0-D7..
any comments would be much appreciated... thanks guys!!!

 

[blueroomelectronics]

You need to post a schematic, code, etc...

 

[futz]

There's working 16F877 code and schematics on my web-site if you want to have a look.

 

[jimi252]

hey.. thanks for the prompt reply guys..
basically I think its a hardware issue since the pic wont work if the LCD is connected to power or to the pic... the second I disconnect the lcd power, the pic turns on. (I put some indicating leds). the schematics are exactly as the ones at your page, futz.. (is that a pullup 10K on R/S pin?? and why??)..
I thought maybe someone can identify this LCD, so I attached some bad quality photos.. on the back it has this yellow sticker that says HMC-16215 SG-LY-12-1 0033, so I searched, and found the manufacturer's page. as expected the datasheets can't be downloaded..

 

[futz]

it has this yellow sticker that says HMC-16215 SG-LY-12-1 0033, so I searched, and found the manufacturer's page. as expected the datasheets can't be downloaded..

Ya, it's a Hitech unit
**broken link removed**

Their site, as you say, is absolutely useless. But most LCDs these days are pretty much standardized.

Yes, a RS pin pullup is needed. 4K7 is enough. I don't see it in my schematic though - guess I forgot. Actually, the EPE schematic I learned from recommends pullups on all lines except R/W and of course Vee, VDD & Gnd. I only did the RS one and it works fine.

 

[jimi252]

yea that's what I believe... but I think both my PICs don't agree so...

 

[futz]

yea that's what I believe... but I think both my PICs don't agree so...

You have enough power? If your power is sagging and can't supply both PIC and LCD then your symptoms might make sense.

 

[jimi252]

just tried the pullups idea.... nothing...
oh.. no my power supply is a badass... its a switching PS from an old pc.. very odd...
check this out... when Vcc of LCD is disconnected, pic works.. when reconnected, pic dies... now, when data wires between pic and lcd are disconnected, pic wakes up again.... very odd... i tried a different pic. and different ports..and this happens with 4/8 bits connected regardless..hehehe!!

 

[futz]

just tried the pullups idea.... nothing...
oh.. no my power supply is a badass... its a switching PS from an old pc.. very odd...
check this out... when Vcc of LCD is disconnected, pic works.. when reconnected, pic dies... now, when data wires between pic and lcd are disconnected, pic wakes up again.... very odd... i tried a different pic. and different ports..and this happens with 4/8 bits connected regardless..hehehe!!

Well you've got something bad going on there. Go over every connection again. Assume nothing. Check everything, no matter how mundane and simple you think it is. It's most likely a silly mistake. I make em all the time.

It could be software too...

 

[eblc1388]

j... when Vcc of LCD is disconnected, pic works.. when reconnected, pic dies... now, when data wires between pic and lcd are disconnected, pic wakes up again.... very odd.

Your PIC has not died. It just loops in an infinite loop for the LCD BUSY check, as most LCD codes do.

 

[donniedj]

Get a decent camera an get a clue on debugging. Not necessarily in that order.

 

[mvs sarma]

just tried the pullups idea.... nothing...
oh.. no my power supply is a badass... its a switching PS from an old pc.. very odd...
check this out... when Vcc of LCD is disconnected, pic works.. when reconnected, pic dies... now, when data wires between pic and lcd are disconnected, pic wakes up again.... very odd... i tried a different pic. and different ports..and this happens with 4/8 bits connected regardless..hehehe!!

Jimi252, Please try to put a schematic as to how you wired it , with maximum details. Perhaps the asm file too would help.

 

[AtomSoft]

Since we are all on the same sort of subject i Have a 2x16 LCD from dipmicro and everything used to work fine untill i unplugged it and tried to use it for 8 bit mode on another board now it doesnt work right on neither of them. Just shows white blocks on lcd and sometimes it will start with futz code from :
**broken link removed**

Im using a 18F1320 without the junebug... The issue is it works when i disconnect and reconnect the power rapidly but only for a few seconds. then back to white blocks... any thoughts?


EDIT: Now it doesnt even show the text on it no more... Is this a LCD issue like stuck in 8 bit mode or something?

 

[futz]

Since we are all on the same sort of subject i Have a 2x16 LCD from dipmicro and everything used to work fine untill i unplugged it and tried to use it for 8 bit mode on another board now it doesnt work right on neither of them. Just shows white blocks on lcd and sometimes it will start with futz code from :
**broken link removed**

Im using a 18F1320 without the junebug... The issue is it works when i disconnect and reconnect the power rapidly but only for a few seconds. then back to white blocks... any thoughts?

EDIT: Now it doesnt even show the text on it no more... Is this a LCD issue like stuck in 8 bit mode or something?

There is no such thing as "stuck in 8-bit mode". Sounds like a power or contrast problem. Sometimes they're the same thing because too little power changes your contrast setting. And they will do that "works for a few seconds" thing. I've seen it. Probably works till the capacitors charge up (probably stupid wild guess)? Fed it decent power and it was fine again. Meanwhile, adjust your contrast and see what happens.

 

[blueroomelectronics]

How are you powering the LCD? From the Junebugs USB power? If so futz's USB might have the oomph to do it but many USB supplies will not (a powered USB hub will)
LCD backlights can draw anywhere from 65ma to 180ma this may cause your USB port to shut down.

 

[AtomSoft]

Its weird and doesnt seem to be a power / contrast issue . Im running offa 7805 and even tried a 317 from a 12v supply so its pretty good and since it used to work and jsut stopped when i took the lcd off and tried something else i think i might have damaged the LCD itself so i guess im going to have to buy some more LCDs to check if its the LCD itself...

 

[AtomSoft]

No there is no Junebug at all in my project just the chip alone with the LCD and a reset circuit thats all...(oh yeha a ICSP circuit) so yeah its powered from either a 9v battery or a 12v-15v transformer plugged into wall with a 7805 as a regulator.... Remember this used to work 100% before i removed it so it might be LCD hardware damaged...

 

[arhi]

Remember this used to work 100% before i removed it so it might be LCD hardware damaged...

Have you removed it while circuit was powered up? I never tried that, but heard, on more place then one, that removing the LCD while circuit is running will kill it.

 

[AtomSoft]

lol actually i have but many times lol maybe thats what happened but its funny since it works sometimes but im sure its dead but heh its only $6 ill buy like 4-5 more and make sure no power before removing next time...

 

[AtomSoft]

Tried it on junebug as exact as possible from futz tutorial and now i get like a flashing 4 block thing that flashes in various locations and ever 2 seconds or so so i assume its the LCD for sure now thanks guys ...