Maximun Cable Length for PIC to LCD

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- 27th November 2007, 16:15
wildbilly

Maximun Cable Length for PIC to LCD

Hello all, I have just finished a project which includes displaying on three LCD displays. Thanks to a great method by Darrel Taylor. http://www.pbpgroup.com/files/2_LCDs.gif
His idea works fantastic. What is the maximum cable length of cable that can be used between Pic and LCD? I have all the three LCD working close to the PIC but 20 feet away I get gibberish. Am I just stuck with a shorter length of cable or is there a work a around.

Thanks.
- 27th November 2007, 18:12
KVLV

i guess max around 2feet for TTL level. if you require longer length i suggest using serial lcd.
- 28th November 2007, 18:27
Darrel Taylor
wildbilly,

Great, glad that's working for you.

I can't answer the main question, as I've never tried to go more than a couple inches to an LCD.
But, I'll agree that serial might be a better way.

However, I think there's two possible sources for the garbled text. And I might be able to do something about one of them if you still want the parallel interface.
1. PBP sends everything out to the LCD at the MINIMUM pulse widths defined in the HD44780 datasheet. Which means approximately 1 Mhz squarewave signals since the enable pulse only lasts 1 uS. That's going to be tuff to get through 20 feet of ribbon cable.
 
2. The other source could be inductive pick-up, like an antenna.
 Can't help much if that's the case.
If the problem is #1? It may be possible to slow down the LCD data to a point that will propagate thru the long ribbon.

Using the technique described in the LCD_Anypin thread, we could create whatever timing is required to slow it down to a reasonable speed.

If you want to try, let me know.
You'll have to do the testing though.
- 28th November 2007, 20:07
wildbilly

Thank you KVLV. I think you are correct about using serial instead. It would be nice though to be able to use the parallel interface. I do enjoy a challenge and it keeps PicBasic interesting.
Thanks Darrel, I have read the LCD_Anypin thread and that is very interesting. I am up for the leg work. I am willing to try and I will do all the testing required.

Thank you.
- 28th November 2007, 20:16
Ioannis

Quote:

Originally Posted by Darrel Taylor

....
2. PBP sends everything out to the LCD at the MINIMUM pulse widths defined in the HD44780 datasheet. Which means approximately 1 Mhz squarewave signals since the enable pulse only lasts 1 uS. That's going to be tuff to get through 20 feet of ribbon cable.

....

Well in this case, I would suggest to use double the number of flat cable wires and the middle ones connected to the ground point. It won't eliminate the problem but will help for sure.

Ioannis
- 28th November 2007, 20:36
mister_e

at very least, if you really want to waste that amount of cable, place some cap close of the LCD VDD/GND (47uF (or greater) + 10 uF tantalum and finally 0.1 uF ceramic)

I don't think there's a real problem with the length of cable so far, my feeling is that you just need to filter the Vdd rail properly at the end and probably play with COMMANDUS & DATAUS DEFINEs.
- 28th November 2007, 23:25
Darrel Taylor

Quote:

Originally Posted by wildbilly

I am up for the leg work. I am willing to try and I will do all the testing required.

Shouldn't take much, but you'll need to install the HighJack routines first.
And you'll also be using the LCD_Anypin files, so download them too.

Start with that, and you should be able to get the LCD working on a Short cable first.

After that, we'll adjust the delays and see what happens on a long one.
If you have any problems getting LCD_Anypin to work, let me know.
- 29th November 2007, 17:04
w7ami

Maximun Cable Length for PIC to LCD

wildbilly,

It should be possible to send data over 20 feet to your display and have it work, but not using ribbon cable. All the conductors are parallel to each other and divided by insulation. In other words you have a bunch of capacitve coupling between the lines. Also the ribbon cable is likely not shielded so any manner of garbage will be picked up from the nearby environment. I have an absolute encoder (10 lines of TTL data) working over a distance of 50 feet in a high RF environment.

First as stated earlier make sure you have cleaned up the power to the LCD with good bypass capacitors with short lead length. You will need to put the displays in some sort of metal box. Then use a shielded cable with twisted pairs (signal and ground on each pair) between the two units. Then if you are still having problems mess with the pulse widths.

Terry
- 1st December 2007, 20:09
wildbilly

2 Attachment(s)

Hello all. As W7AMI suggested, I have tried filtering the supply and I have changed the cable to shielded pairs but no luck. Darrel I have installed the Highjack routines and also included the LCD_Anypin.pbp and VirtualPort.bas in the PBP folder. I then added the Include file in my main program just below the define Parameters.

INCLUDE "LCD_AnyPin.pbp"
I am using MicroCode Studio and when compile is run I get the error
Line 87:Bad expression. (LCD-AnyPin.pbp)
The LCD_AnyPin file is opened and the line LOW LCD_RS : HIGH LCD_E is highlighted causing the error. I have included two images. The green Display is connected on the short cable and the Blue Display is connected to the long cable. As you can see blue is not displaying what the green is and the character on the blue display is constantly changing.
- 1st December 2007, 20:25
Charles Linquis

I think the problem is that it is just plain too cold where you live!
- 1st December 2007, 20:37
wildbilly

That's a good laugh. I thought someone would have that reply.
- 1st December 2007, 21:39
Darrel Taylor

Quote:

Originally Posted by wildbilly

Darrel I have installed the Highjack routines and also included the LCD_Anypin.pbp and VirtualPort.bas in the PBP folder. I then added the Include file in my main program just below the define Parameters.

Excellent!

Does your main program have this section (modified for your hardware of course).
The old lcd DEFINES can be commented out.

Code:

;----[ Change these to match your LCD ]--------------------------------------- LCD_DB4 VAR PORTA.0 LCD_DB5 VAR PORTB.3 LCD_DB6 VAR PORTB.7 LCD_DB7 VAR PORTC.1 LCD_RS VAR PORTD.4 LCD_E VAR PORTA.1 LCD_Lines CON 2 ' # of Lines on LCD, 1 or 2 (Note: use 2 for 4 lines) LCD_DATAUS CON 50 ' Data delay time in us LCD_COMMANDUS CON 2000 ' Command delay time in us INCLUDE "LCD_AnyPin.pbp" ; *** Include MUST be AFTER LCD Pin assignments ****
- 1st December 2007, 23:08
wildbilly

Hi Darrel. I added the list below and no longer have the error but no longer have a display on
the LCD. I only have two black bars.

'LCD_DB4 VAR PORTB.0
'LCD_DB5 VAR PORTB.1
'LCD_DB6 VAR PORTB.2
'LCD_DB7 VAR PORTB.3
'LCD_RS VAR PORTB.4
'LCD_E VAR PORTB.7

The list below works fine.

'LCD Parameters
'============
DEFINE LCD_DREG PORTB ' LCD Data port
DEFINE LCD_DBIT 0 ' starting Data bit (0 or 4) if 4-bit bus
DEFINE LCD_RSREG PORTB ' LCD Register Select port
DEFINE LCD_RSBIT 4 ' LCD Register Select bit
DEFINE LCD_EREG PORTB ' LCD Enable port
DEFINE LCD_EBIT 7 ' LCD Enable bit
DEFINE LCD_BITS 4 ' LCD bus size (4 or 8 bits)
DEFINE LCD_LINES 4 ' Number of lines on LCD
DEFINE LCD_COMMANDUS 2000 'Command delay time in us
DEFINE LCD_DATAUS 50 'Data delay time in us

My LCD is connected just like your example " http://www.pbpgroup.com/files/2_LCDs.gif
- 1st December 2007, 23:59
Darrel Taylor

Bummer,

OK, let me re-create it here.
Back at ya soon.
- 2nd December 2007, 03:18
Darrel Taylor

OK,

Just to make sure, I went thru the steps again myself.
Have it working here on a 16F88. One thing I had to add that wasn't mentioned here, although it was in the other thread ...

Code:

PAUSE 500 : LCDOUT $FE,1 : PAUSE 250 ; Initialize LCD (You may not need this, ; but some displays are picky)

But so that I can compare Apples to Apples, What PIC are you using?

I bought 25ft of ribbon today, just to make sure. But haven't hooked it up yet.
- 2nd December 2007, 03:22
wildbilly

I added the code
PAUSE 500 : LCDOUT $FE,1 : PAUSE 250 ; Initialize LCD
with the same result. I am using the 16F877a
- 2nd December 2007, 06:38
Darrel Taylor

Apples it is .. :)

Built a 16F877A breadboard. With LCD on the above mentioned ports.
Still haven't hooked up the ribbon yet, just wanted 1 LCD at this point.

Here's the Breadboard.
http://www.pbpgroup.com/files/wildbilly_BB_sm.JPG
Click image to enlarge

And here's the program it's running.

Code:

@ __config _HS_OSC & _WDT_OFF & _LVP_OFF & _CP_OFF ADCON1 = 7 CMCON = 7 DEFINE OSC 4 ;----[ Change these to match your LCD ]--------------------------------------- LCD_DB4 VAR PORTB.0 LCD_DB5 VAR PORTB.1 LCD_DB6 VAR PORTB.2 LCD_DB7 VAR PORTB.3 LCD_RS VAR PORTB.4 LCD_E VAR PORTB.7 LCD_Lines CON 2 ' # of Lines on LCD, 1 or 2 (Note: use 2 for 4 lines) LCD_DATAUS CON 50 ' Data delay time in us LCD_COMMANDUS CON 2000 ' Command delay time in us INCLUDE "LCD_AnyPin.pbp" ; *** Include MUST be AFTER LCD Pin assignments **** PAUSE 500 : LCDOUT $FE,1 : PAUSE 250 ; Initialize LCD (You may not need this, ; but some displays are picky) LCDOUT $FE,1,"Hello wildbilly",$FE,$C0,"Must be something",$FE,$94,"In the Hardware" Main: ; toggle LED pause 1000 goto Main

Can you see anything I've done different??
- 2nd December 2007, 13:57
wildbilly

Your apple must be the Macintosh because yours is working and mine is not.
Ok, here is what I have found. I have loaded your code to a new main program and could not compile it. I am getting this error: "opcode expected instead of '_config' "
for this line @ __config _HS_OSC & _WDT_OFF & _LVP_OFF & _CP_OFF

and I get these errors for this line : INCLUDE "LCD_AnyPin.pbp"
"opcode expected instead of 'writeport' "
"opcode expected instead of 'delayus' "
"opcode expected instead of 'outputport' "

I have checked the Hijack code included in the PBPPIC14.lib file and I think it was modified correctly. Any clues?

Thanks
- 2nd December 2007, 19:39
Darrel Taylor

1 Attachment(s)

Quote:

I am getting this error: "opcode expected instead of '_config'

Ah Ha, You aren't using MPASM as the assembler.

Almost anything written with ASM mixed in the program, needs to be compiled with MPASM. The assembler that comes with PBP is OK for PBP itself, but it just doesn't have the capabilities needed for ASM, even though sometimes it will compile OK.

Here's a hex file for mine if you want to try it.
If yours isn't runnung at 4Mhz, I'll change it to your crystal.
- 2nd December 2007, 20:12
Ioannis

Quote:

Originally Posted by Darrel Taylor

Apples it is .. :)

Built a 16F877A breadboard. With LCD on the above mentioned ports.
Still haven't hooked up the ribbon yet, just wanted 1 LCD at this point.
 

I can't add anything more on Darrels suggestions, but have to admit that the breadboard is very tidy good looking! An art in breadboarding!

The background that seems like a pcb, what is it?

Ioannis
- 2nd December 2007, 20:58
Darrel Taylor

Thanks for noticing Ioannis,

The first breadboard I ever bought came with a box of 3M pre-cut jumpers.
I just thought that's the way it's supposed to be done.

Thanks to my "Glowing Eyed Monsters",
I also learned to trim the leads off of the parts so they sit flat on the breadboard.
There's another breadboard of mine in that thread too. Same style.

I never knew how bad a breadboard could be till I ran across this ... :eek:
http://cs.nyu.edu/~jhan/ledtouch/
- 2nd December 2007, 20:59
wildbilly

Yeah! He is indeed very neat. I am inspired to do the same. The background looks like a chair seat. Darrel your wildbilly.hex file ran ok. I have never used MPASM. I should try and get it going.

Thank you.
- 2nd December 2007, 21:25
Darrel Taylor

Quote:

The background looks like a chair seat.

DING! Give that man a cigar. :)
I forgot to answer it. oops.

Quote:

I have never used MPASM. I should try and get it going

Just go here... at the bottom of the page, install the MPLAB IDE v8.00 Full Release Zipped Installation
http://www.microchip.com/stellent/id...&part=SW007002

Are you using MicroCode Studio for the IDE?
- 2nd December 2007, 21:40
mister_e

one of the less neat prototype i've never ever saw ...
http://www.botmag.com/articles/bionic_stamp.shtml

:D
- 3rd December 2007, 00:23
wildbilly

Hi Darrel. I am using Microcode Studio.
- 3rd December 2007, 00:47
Darrel Taylor

Great. That makes it easy.

After installing MPLAB ...

In MCS, go to the View | Compile and Program Options | Assembler Tab

Click the Find Manually ... button and point it to
C:\program files\microchip\mpasm suite

Then check the Use MPASM checkbox.

You should be good to go.
- 3rd December 2007, 00:55
Darrel Taylor

OOPs, one more thing to get that to compile.

In your PBP folder, open the 16F877A.INC file, and comment out the __config line with a semicolon ;

Now you should be good to go.

mister_e,

At least now I know where to go if I need some extra wire.
Sheesh. :)
- 3rd December 2007, 02:40
wildbilly

Hi Darrel. I have installed MPLAB IDE v8.00 Full Release and setup was done as mentioned.
Now when compiled I get the MPASM window showing the process and then shows 18 errors.
This goes by very fast and starts green and then goes red. The errors are similar to what I had before. Here are a few. I have omitted the path for each error.

205 : Found label after column 1. (WritePort)
205 : Illegal opcode(_Char)
234 : Illegal opcode(_LCD_DATAUS)
249 : Found label after column 1.(DelayUS)
267 : Illegal opcode(LCD_COMMANDUS)

and many more
- 3rd December 2007, 03:24
Darrel Taylor

Arrrrgh!

Sorry to put you thru all this, it shouldn't be that hard.

I can't really say what's happening from the errors you showed.
I could probably see what's wrong if you could send the .LST file.

It'll be too big to post, but you could email it to
darrel at pbpgroup.com

It should've worked :o
- 3rd December 2007, 13:08
nomad

you all must have cringed when i posted my first blinky on bread board. lol mine are true ratsnests. guess it's time to buy some neato jumpers and stop being a disgrace. sniff lol
- 3rd December 2007, 15:11
mister_e

Quote:

Originally Posted by Darrel Taylor

mister_e,

At least now I know where to go if I need some extra wire.
Sheesh. :)
 

Have a look at the last lines of the link... About The Author.. :eek: i'm afraid
- 3rd December 2007, 15:54
mackrackit

Quote:

Have a look at the last lines of the link... About The Author.. i'm afraid

And to think I did not have to go to school to be that messy:)
- 4th December 2007, 09:10
dideco

A CMOS chip as a buffer (such as 4050) can be added to the parallel cable to use longer wires. Also some resistors will help to make a kind of current loop by placing 2.2-4.7 Kohms close to inputs of the LCD unit.

LCD_Lines CON 2 ' # of Lines on LCD, 1 or 2 (Note: use 2 for 4 lines)
LCD_DATAUS CON 50 ' Data delay time in us
LCD_COMMANDUS CON 2000 ' Command delay time in us

"Data delay time" should be longer, such as 500 microseconds or longer. This will help the commads to reach display safely. Pulse decreases because of cable capacitance and resistance (RC time constant). LCD displays can load data in its register buffers in a very short period but cannot execute it as fast as loading. Thats why command delay time is 40 times longer.
- 8th December 2007, 19:06
wildbilly

2 Attachment(s)

Thanks Dideco for your input, I will carry on with Darrel's method for now as I find it quite interesting and I have been at it for a while. Darrel, here is what I have found so far. I have been able to get your Hijack routines to work without any errors. I am now able to see a perfect display on long lengths of cable. I have tried 20 to 40 ft of 22 awg multi-cable and the display is perfect. I did not need to adjust any delays. I have not been able though, to get the displays to switch properly using the method you described for your 2 LCD's on one pic display method. Have a look at Display_1 and you will see the display is correct using your sample code. On Display_2 you will notice that there are problems on both displays when using the hijack routines.

Thanks.
- 8th December 2007, 20:43
Darrel Taylor

HI wildbilly,

Sounds like your up to speed with me now. http://www.picbasic.co.uk/forum/images/icons/icon14.gif

I've been bogged down all week with work, so I'm kind of glad you had problems.
I'm sure it's not the same from your point of view.

So anyhow, I've found that the resistors used to select each display seem to act as a filter with the extra capacitance of the ribbon. The enable line gets rounded off pretty bad.

Fortunately, with "HighJack", we're not limited to just one Enable pin anymore.
We can have as many as needed. And that's the next step.

We'll use the previous "Disable" pins as the "Enable" line for each LCD. The resistors are no longer needed. Then instead of Disabling the display you don't want to write to, you'll Enable the one's you do want.

This takes a few modifications, but it's not too bad.

First, in the main program, change the LCD definitions to this ...

Code:

;----[ Change these to match your LCD ]--------------------------------------- LCD_DB4 VAR PORTB.0 LCD_DB5 VAR PORTB.1 LCD_DB6 VAR PORTB.2 LCD_DB7 VAR PORTB.3 LCD_RS VAR PORTB.4 LCD_E1 VAR PORTB.5 LCD_E2 VAR PORTB.6 LCDEN VAR BYTE BANK0 ; Enable bits for each LCD LCD1EN VAR LCDEN.0 LCD2EN VAR LCDEN.1 LCD_Lines CON 2 ; # of Lines on LCD, 1 or 2 (Note: use 2 for 4 lines) LCD_DATAUS CON 50 ; Data delay time in us LCD_COMMANDUS CON 2000 ; Command delay time in us INCLUDE "LCD_AnyPin.pbp" ; *** Include MUST be AFTER LCD Pin assignments **** LOW LCD_E1 ; Start with Enables OUTPUT LOW LOW LCD_E2

Next, in the LCD_AnyPin file, there's a section that says "DO NOT Change anything below this line".
Change it to this ... :)

Code:

ASM LCD_Port_HNIB macro ; Port definition for LCD High Nibble Vbit LCDCDFLAG, _LCD_RS ; Select Command/Data register DelayUS 2 NOP Vpin 4, _LCD_DB4 ; Put the High Nibble on the bus Vpin 5, _LCD_DB5 Vpin 6, _LCD_DB6 Vpin 7, _LCD_DB7 DelayUS 2 btfsc _LCD1EN ; Set enable(s) High bsf _LCD_E1 btfsc _LCD2EN bsf _LCD_E2 DelayUS 5 ; hold for 5us bcf _LCD_E1 ; Enable(s) Low - Clocks data bcf _LCD_E2 endm ;----------------------- LCD_Port_LNIB macro ; Port definition for LCD Low Nibble Vpin 0, _LCD_DB4 ; Put the Low Nibble on the bus Vpin 1, _LCD_DB5 Vpin 2, _LCD_DB6 Vpin 3, _LCD_DB7 DelayUS 2 btfsc _LCD1EN ; Set enable(s) High bsf _LCD_E1 btfsc _LCD2EN bsf _LCD_E2 DelayUS 5 ; hold for 5us bcf _LCD_E1 ; Enable(s) Low - Clocks data bcf _LCD_E2 endm ENDASM

And finally, also in the LCD_AnyPin file, change LCD_Init to this ...

Code:

;----[Initialize the LCD]-------------------(DO NOT Change)------------------- LCD_Init: @ OutputPort LCD_Port_HNIB ; Set LCD bus to OUTPUT LCDEN = 1 + 2 LOW LCD_RS ; Start with RS LOW Char = 3 : gosub LCDsendShortCOM : @ DelayUS 6000 gosub LCDsendShortCOM : @ DelayUS 1000 gosub LCDsendShortCOM : @ DelayUS 1000 Char = 2 : gosub LCDsendShortCOM : @ DelayUS 1000 ; Start 4-bit mode Char = $28 : gosub LCDsendCOM ; Function Set, 4-bit, 2-line, 5x7 Char = $0C : gosub LCDsendCOM ; Display ON Char = $01 : gosub LCDsendCOM ; Clear Screen Char = $06 : gosub LCDsendCOM ; Entry Mode LCD_Initialized = 1 ; LCD has been Initialized goto LCDAfterInit

http://www.pbpgroup.com/files/100_0279_sm.JPG
Click image to enlarge.

P.S. Until now I thought that 6 inches was the limit for LCD's. Just because somebody told me that once.
This is really cool. Thanks for the interesting things to play with.<hr>

ADDED: Oops, forgot to show you how to use it..

Code:

LCDEN = 1 LCDOUT $FE,1, "Display 1" LCDEN = 2 LCDOUT $FE,1, "Display 2" LCDEN = 1 + 2 LCDOUT $FE,$C0, "Both Displays"
- 9th December 2007, 03:47
wildbilly

Thanks Darrel. I have it working. I just need to check it again on the long cable. The displays are flashing. How do I stop that? I suppose that is something in the "LCD_AnyPin" file.
- 9th December 2007, 03:52
Darrel Taylor

If it's a Fast Flash?
Are the LCDOUT statements running in a loop?

If so, try using $FE,$80 instead of $FE,1
- 9th December 2007, 04:14
wildbilly

Thanks Darrel. That did it. I will check the long cable in the morning. Thank you for your help.
- 9th December 2007, 04:18
wildbilly

I am going to try and add a third display. I will let you know how I make out. In your original sample code I had modofied it for three displays and it worked ok. I will give it a try.
- 9th December 2007, 10:10
Darrel Taylor

1 Attachment(s)

3 LCD's

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2185&stc=1&d=119719494 4" />

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