LCD problem - Electronic Circuits Projects Diagrams Free

Night Rider · 2nd April 2008, 02:46 PM

Hi guys!
I have a problem and i can't understand what kind of problem is that. I made a power supply for my bench. I made two channels 0-30V and one channel -30V-0V. Also i put 0.1ohm resistors to measure the current of all three channels. Then i decided to display the voltages and the currents via 2x20 LCD controlled by a PIC16F877. I transformed the voltages and the currents with op amplifiers to bring them at 5V maximum at the six analog pins of the uC. I wrote the program, i burned the pic, i turned the switch on and the problem is that the LCD displays nothing except if i put my fingers on the pins DB4, DB5, DB6, DB7. Only then the LCD displays and working as i programmed the pic. I drive the LCD with four pins data and not with the eight. 4Mhz clock for the pic. It is the first time i saw this kind of problem at pic-LCD's. Is the problem to the connector? Cold soldering perhaps?
Please help!

ericgibbs · 2nd April 2008, 02:49 PM

Do you have the LCD's 'contrast' pin connected.?

Night Rider · 2nd April 2008, 02:58 PM

Yes, it's all ok. I played with the contrast and the light.

Pommie · 2nd April 2008, 03:04 PM

Disconnect everything except the pic, the LCD and a 5V supply. Then try to get it to display "Hello World!". If it doesn't work then post your code and a schematic and we should be able to help you get it working. Then you can go on to other things.

Mike.

Night Rider · 2nd April 2008, 03:08 PM

Ok guys, thanks. I'll search it more and i'll tell you the results.

ericgibbs · 2nd April 2008, 03:10 PM

Quote:

Originally Posted by Night Rider

Yes, it's all ok. I played with the contrast and the light.

I am assuming that the DB7 thru DB4 are the pins that are wired and that DB3 thru DB0 are floating.

You say you can change the contrast of the LCD pixels using the pot OK.

When you hold your fingers on the pins it adds capacitance and the LCD pulse edges are degraded, that is, the rise/fall times are increased.

Can you increase the LCD 'enable line' time periods, [within the program] as a test,?

Night Rider · 3rd April 2008, 04:18 PM

Ok, i made a lot of projects with this type of program and are working fine. I'll test this. I played a little with the voltage and current at the contrast and at the supply and worked. I'll try to make it perfect.
Thanks!

Night Rider · 5th April 2008, 01:29 PM

I built the circuit on a raster and it works perfect. So, the problem i supposed is at the pcb. But i can't believe i'm telling this, because there is no shortcircuit, there is no opencircuit after a detailed test. Also i observed that when i'm placing far the crystal with the two capacitors, the oscilator circuit, it failed for the most times(at the raster). But at the pcb the oscilator circuit is only 2cm far from the uC. There is nothing else connected to the uC. Here is a foto of the pcb. The two wires are for 5V LCD supply. Rather i'll make another pcb to test it. Thanks all for your thoughts.

Night Rider · 5th April 2008, 01:36 PM

Here are the fotos

mvs sarma · 5th April 2008, 02:10 PM

please put a 0.1uF MLC cap across Vdd and Vss close to the PIC chip. I didn't fine one. perhaps this might help to normalize

blueroomelectronics · 5th April 2008, 04:08 PM

It doesn't appear all the VDD & VSS pins are connected. You need to connect them all.

mvs sarma · 5th April 2008, 04:48 PM

Congrats Bill,You got it,

Pins 11 and 12 not used .

blueroomelectronics · 5th April 2008, 04:50 PM

Quote:

Originally Posted by mvs sarma

Congrats Bill,You got it,

Pins 11 and 12 not used .

Actually both answers yours and mine are essential. Was there any large filter cap on the board? That'll help too.

mvs sarma · 5th April 2008, 05:32 PM

Quote:

Originally Posted by blueroomelectronics

Actually both answers yours and mine are essential. Was there any large filter cap on the board? That'll help too.

Many a time, people are pushing projects without any filter components. Few examples are very accurate LC meter from www.electronics-diy.com and few projects from www.josepino.com like LCD clock cum calender. Most of these don't contain needed Vdd line filters.

blueroomelectronics · 5th April 2008, 05:53 PM

The 0.1uf caps are important enough you could buy IC sockets with 0.1uf caps built in for TTL ICs.
I wish simulators would complain if you didn't have them.

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2nd April 2008, 02:46 PM	(permalink)
Night Rider	LCD problem Hi guys! I have a problem and i can't understand what kind of problem is that. I made a power supply for my bench. I made two channels 0-30V and one channel -30V-0V. Also i put 0.1ohm resistors to measure the current of all three channels. Then i decided to display the voltages and the currents via 2x20 LCD controlled by a PIC16F877. I transformed the voltages and the currents with op amplifiers to bring them at 5V maximum at the six analog pins of the uC. I wrote the program, i burned the pic, i turned the switch on and the problem is that the LCD displays nothing except if i put my fingers on the pins DB4, DB5, DB6, DB7. Only then the LCD displays and working as i programmed the pic. I drive the LCD with four pins data and not with the eight. 4Mhz clock for the pic. It is the first time i saw this kind of problem at pic-LCD's. Is the problem to the connector? Cold soldering perhaps? Please help!

2nd April 2008, 02:49 PM	(permalink)
ericgibbs	Do you have the LCD's 'contrast' pin connected.? __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

2nd April 2008, 02:58 PM	(permalink)
Night Rider	Yes, it's all ok. I played with the contrast and the light.

2nd April 2008, 03:04 PM	(permalink)
Pommie	Disconnect everything except the pic, the LCD and a 5V supply. Then try to get it to display "Hello World!". If it doesn't work then post your code and a schematic and we should be able to help you get it working. Then you can go on to other things. Mike.

2nd April 2008, 03:08 PM	(permalink)
Night Rider	Ok guys, thanks. I'll search it more and i'll tell you the results.

3rd April 2008, 04:18 PM	(permalink)
Night Rider	Ok, i made a lot of projects with this type of program and are working fine. I'll test this. I played a little with the voltage and current at the contrast and at the supply and worked. I'll try to make it perfect. Thanks!

5th April 2008, 01:29 PM	(permalink)
Night Rider	I built the circuit on a raster and it works perfect. So, the problem i supposed is at the pcb. But i can't believe i'm telling this, because there is no shortcircuit, there is no opencircuit after a detailed test. Also i observed that when i'm placing far the crystal with the two capacitors, the oscilator circuit, it failed for the most times(at the raster). But at the pcb the oscilator circuit is only 2cm far from the uC. There is nothing else connected to the uC. Here is a foto of the pcb. The two wires are for 5V LCD supply. Rather i'll make another pcb to test it. Thanks all for your thoughts.

5th April 2008, 02:10 PM	(permalink)
mvs sarma	please put a 0.1uF MLC cap across Vdd and Vss close to the PIC chip. I didn't fine one. perhaps this might help to normalize __________________ Regards, Sarma.

5th April 2008, 04:08 PM	(permalink)
blueroomelectronics	It doesn't appear all the VDD & VSS pins are connected. You need to connect them all. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

5th April 2008, 04:48 PM	(permalink)
mvs sarma	Congrats Bill,You got it, Pins 11 and 12 not used . __________________ Regards, Sarma.

5th April 2008, 05:53 PM	(permalink)
blueroomelectronics	The 0.1uf caps are important enough you could buy IC sockets with 0.1uf caps built in for TTL ICs. I wish simulators would complain if you didn't have them. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com