16x2 Parallel LCD display not working....

jknightandkarr

I have this LED screen topwaydisplay.com/Pub/Manual/LMB162ABC-Manual-Rev0.2.pdf and using the Programming the Propeller with Spin: A Beginner's Guide to Parallel Processing text. Now both the text and the manual shows the connections as the same, but all I get is the backlight and the top row of characters solid on. Using the program in Ch 14. What could the reason for the display not working??? Thanks.

Joe

Chris Savage

Exactly how do you have the display wired up? The backlight shouldn't come on unless it is wired up independently. Not as part of the driver working, since that display didn't have a backlight.

jknightandkarr

Exactly as the chapter in the book shows it, minus the contrast adjustment, which is wired through a 10k pot on my ppdb. The backlight is wired straight to 5v+ n gnd, but its the characters on the screen just 16 blocks that don't change. The 2nd row on the display stays off. I thought the displays used similar controllers. I checked on that one time, will double check it.

Joe

Chris Savage

So you're not doing it like shown in the book? It sounds like you're using the PPDB?

JonnyMac

You will occasionally run into displays that have a negative contrast voltage requirement -- I certainly have. Connect the ends of a 10K pot between 5V and GND, then connect the wiper to the contrast pin. You should see the contrast change as you move the pot. Note, though, that the final adjustment needs to be after the LCD is initialized to two lines.

I have attached my LCD object in case you want to give it a try. It is well wrung out, and is in use in a few commercial projects.

Note that with a 4-bit interface I don't use the read mode of the display, hence this code is write-only. If you need code that can read from the display, I have that, too.

jknightandkarr

With the exception of the contrast ground n backlight being used, they are wired the same way. Yes, I am using the PPDB on it.

Joe

jknightandkarr

JonnyMac wrote: »

You will occasionally run into displays that have a negative contrast voltage requirement -- I certainly have. Connect the ends of a 10K pot between 5V and GND, then connect the wiper to the contrast pin. You should see the contrast change as you move the pot. Note, though, that the final adjustment needs to be after the LCD is initialized to two lines.

I have attached my LCD object in case you want to give it a try. It is well wrung out, and is in use in a few commercial projects.

Note that with a 4-bit interface I don't use the read mode of the display, hence this code is write-only. If you need code that can read from the display, I have that, too.

I got the contrast adjustment working well. I will try your object. It could be the program i am using. The one from the book but got it from encodergeek.com that could be the issue as well

Joe

jknightandkarr

Ok, checked the program on encodergeek.com and in the book. I haven't found any differences. I guess next step is whats the difference in the Hitachi HD44780 (used in the book) vs the Samsung S6A0069 (My LCD display)??

Joe

JonnyMac

Sorry, I missed that.

I have attached a full demo here that is actually running on a client project (laser-tag controller interface with 2x8 LCD), so I know it works. You'll just need to change the IO pins to match your setup.

jknightandkarr

Here is a pic of the display, and the issue.

Joe

JonnyMac

When in doubt, pull the wires out and put them back very carefully. I do a lot of solderless breadboarding (have designed products on the Propeller PDB) and sometimes just taking a few minutes to reset the wiring does the trick.

You picture shows an LCD that is not initializing.

jknightandkarr

I wonder why?

Joe

JonnyMac

Bad connection? Try re-wiring.
Bad pin? Try different pins.

jknightandkarr

Maybe if I try my BS2 n go from there? Always worth a try.

Joe

JonnyMac

That would be one way to verify the LCD.

DigitalBob

I just have one question did you drop the lcd on the floor? The lcd is more delicate than it looks I know because I've drop check one before and it looks like that.

Toby Seckshund

I have had similar problems with some 2 x 16/20 LCDs. I have never proven that it is the case but as the ones I had problems with the Prop (3.3V) seem to work OK with AVRs (5V) I put it down to them being 3.3V unfriendly.

macrobeak

Yup Toby, you are right. I have had problems with the 2 x 16 LCD's not working properly with Prop 3.3v pins, but working fine with Basic Stamp 5v pins.
Eventually I had to use a voltage level shifter to ensure reliable operation of the LCD with 3.3v pins.
This was very hard to troubleshoot. You are not sure if it is your code, wiring, LCD or what.
Luckily I had an "old" 2 x 16 LCD which DID work with 3.3v pins and by trial and elimination I was able to work it out.

JonnyMac

Check the Vcc spec on the LCD. On a client job I was forced to us an LCD that was not always happy with 3.3V signals from the Propeller. I put a schottky diode in the Vcc line to bring that down a bit; this changed the internal threshold enough that the LCD never gave me any more problems. Not ideal, I know -- again, I was forced by the client (upgrading from PIC) to use a particular LCD.

You might try a 1N5817 in the Vcc line of the LCD to see if that helps (this is after you confirm the LCD works fine with 5V signals).

idbruce

Nice tip Jon.

I once had one those LCDs that required 5V, and sure could have used that tip back then.

jknightandkarr

DigitalBob wrote: »

I just have one question did you drop the lcd on the floor? The lcd is more delicate than it looks I know because I've drop check one before and it looks like that.

No it hasn't been dropped at all. It's been in a breadboard since I got it, which is the PPDB, which wasn't dropped anytime.

JonnyMac wrote: »

Check the Vcc spec on the LCD. On a client job I was forced to us an LCD that was not always happy with 3.3V signals from the Propeller. I put a schottky diode in the Vcc line to bring that down a bit; this changed the internal threshold enough that the LCD never gave me any more problems. Not ideal, I know -- again, I was forced by the client (upgrading from PIC) to use a particular LCD.

You might try a 1N5817 in the Vcc line of the LCD to see if that helps (this is after you confirm the LCD works fine with 5V signals).

I think that's the problem. I found a line saying in the manual "Input High Voltage =0.8xVdd" which at 5v is like 4v and Min Vdd is 4.7 V so will need something between the signal pins and the led screen for it to function properly, buffer logic gates might work.
Joe

DigitalBob

I see your running a out of the box chiwan lcd. You could buy the spi adapter will cost about $3-$4 and run it that way. Don't know if you want to incur the cost and shipping. MPJA is a low cost source.

DigitalBob

HD44780 controller

jknightandkarr

I will check that out. Tried to find one before but couldnt find a source of them by themselves, through my known normal places anyhow. Will check that MPJA out. Thanks!

They could have included that with the rest of the stuff in that Make: Arduino kit.... That and a freaking datasheet/instructions! Pretty much parts list n your on your own... No manual for ANYthing, no learning or labs type material, just the parts n parts list. Litterally nothing else. Kinda surprise to me from something picked up at Radio Shack.

Joe

DigitalBob

At least with a serial controller lcd you can run a prop object. The parallax ones are a little pricey but nice

DigitalBob

Look on mpja they have data sheet for the lcd and controller