HD44780 compatible PLED 16x2 display not working!!! - Page 1
Forum section: electronics / general

author: sdttn
author_rank: Contributor
timestamp: September 08, 2011, 09:37:40 am
content: Hello,I bought 4 pcs of pled display from ebay. But I couldn't figured out how they are working.I wrote some code for hd44780 display, the code working with regular I am using 16f877 @4Mhz, code wrote in pic basic. I tried 4 bit connection and 8 bit connection.The code working with regular LCD but the code not working with PLED display.I added the datasheet of the PLED displays.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: September 08, 2011, 10:20:39 am
content: Try this linkhttp://www.epemag.wimborne.co.uk/resources.htmYou can test your HD44780 controller with no more than a few switches to confirm it's operation, then you need to check your code. Are you sure that the controller is an HD44780? I thought these were for LCD Displays?<Edit > Just read the data sheet () and it is indeed compatible with the HD44780. Just one thought ,have you tried adjusting the contrast pot? caught me out more than once?

author: ElektroQuark
author_rank: Unknown
timestamp: September 08, 2011, 10:44:39 am
content: Yes, you MUST adjust the contrast with some of those displays or you will see only a clear or dark screen.

author: sdttn
author_rank: Contributor
timestamp: September 08, 2011, 04:22:16 pm
content: Thanks for your replies.In datasheet the brightnes (Contrast in regular LCDs) pin needs 3 volts to go. I adjusted the pot at 3 volts and other positions. It does not work.Any ideas?Edit:The code working with regular LCDs (HD44780)

author: FreeThinker
author_rank: Frequent Contributor
timestamp: September 08, 2011, 06:24:08 pm
content: Have youa) Tested the displays manually to confirm operation?b) Substituted a lcd display to confirm your hardware/ code? (may be the most productive option)If Both check out ok then it is likely a timing problem (I've only skimmed the data sheet but HD44780 compatable SHOULD mean just that and timing should not be an issue but it's worth checking ) last but not least could be power supply issues, what sort of load does it take, is the supply stable and clean?

author: Bored@Work
author_rank: Super Contributor
timestamp: September 08, 2011, 07:55:50 pm
content: There is rarely a new module with an original HD44780 any more, since that IC isn't manufactured since ages. New HD44780 displays use clones of different quality, and with timing variations from the original HD44780.HD44780 timing, including clones is a bitch. Many code for HD44780 out there has wrong timing and just worked on one or the other HD44780 clone. People unfortunately think when it happened to work for them it will work for everyone and publish that code.Therefore, carefully go through the datasheet for your module and notice all the timing (delay) values. Adhere to them. Every time. And not only that. Add a safety margin to them, since your CPU clock might be a little bit off, and your module might have a bad hair day. If you can, measure the timing of your signals with an oscilloscope or LA. Don't just trust that the timing looks ok in the software. Especially, don't trust delay loops. Your compiler might have optimized them out.Another issue with those HD44780 clones is their behavior when it comes to unconnected data and control lines compared to the original HD44780. Carefully connect all pins just for good measure. Including grounding unused pins or tying them to Vcc. Many HD44780 clones don't need this, but some do.Yet another issue is reset. On paper a HD44780 or clone initializes itself after reset automatically, and the typical sequence to initialize it is not needed. In reality this barely works, because it requires power rising at a certain speed. So in reality you can not skip the initial instruction sequence. And that sequence must be given with the right timing, otherwise you end up at with an uninitialized display.And yes, correctly adjust the contrast.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: September 08, 2011, 08:13:25 pm
content: Very well put B@W, as I have said in my previous post you need to confirm which parts are working (and by definition which parts are not) then you can start to debug. Timing issues are a real PITA and need to be checked thoroughly but you need to eliminate the easier options first (dead display, wiring issue, hardware problem etc). A fuller discription of the circuit/hardware/ software etc would also help.

author: sdttn
author_rank: Contributor
timestamp: September 09, 2011, 07:34:21 am
content: Quote from: FreeThinker on September 08, 2011, 06:24:08 pmDo you mean test with swiches?@BoredAtWorkI am just hobbyist I dont have oscilloscope or LA.Maybe picbasic pro the compiler sucks about timing.,I will try to find any other codes and change the oscillator with 8Mhz one.BTW I cant see anything on pled displays when they are powered and also wired to mcu.Thank you.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: September 09, 2011, 10:17:19 am
content: Yes , just connect the display up as in the pdf I linked to and go through the article one step at a time. I know it is for a lcd but the same tests should still apply. Once you know that the display works as it should you can test the hardware for functionality (ie the pic or atmel or whatever) knowing that the display is good. Also try it with a known good lcd if you have one (this will eliminate/ identify problems between display types). Once you have proven the display and the mpu + wiring all that is left is software or timing issues. Without the correct test equipment you will struggle to sort that one so your best bet is to concentrate on the hardware for the moment and hope you find something.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: September 09, 2011, 11:23:52 am
content: Well a bit of poking around on the net shows that Pled technology/ production was stopped circa 2008 and all products based on it obsoleted. Based on that I would be very suspicious of any display based on it unless from a known supplier (digikey farnell etc).http://www.directindustry.com/prod/one-stop-displays/pled-displays-34011-197554.htmlwas one of many announcements I found. Unless production has restarted I would avoid them.

author: BBQdChips
author_rank: Contributor
timestamp: September 17, 2011, 05:34:00 pm
content: Quote from: sdttn on September 08, 2011, 04:22:16 pmSetting to 3V will set the contrast to minimum, not max.To increase contrast, decrease the contrast signal. 0V works great.