16X2 LCD display ESD immunity - Page 1
Forum section: electronics / projects

author: mcinque
author_rank: Unknown
timestamp: August 09, 2014, 01:40:57 pm
content: Hello,I'm trying to figure how to avoid problems on a classic Hitachi 16x2 LCD display when some ESD happens in contact oreven in air.The display is driven by an Atmega328P that is not affected by the ESD events: there is a long led bar near the LCD that bounces up and down, just to understand if the MCU resets or stops the code during the ESD.Actually to test the behaviour of the display, I'm using a BBQ igniter that produces sparks up to 2CM long (so a big voltage, during sparks I can feel the typical ozone smell); the manufacturer say >12.000V.When the static discharges onto the LCDor even in air, the characters on the display become scrambled, and even the MCU continue running the code (the led bar keeps bouncing), the display remain in this scrambled state until I disconnect and reconnect the power.So this appear to be only an issue on the internal LCD logic driver.Since I didn't solve anything by using TVSs, probably the best thing to do is to make the code refresh the screen every X seconds to clear that mess, but can you suggest me another solution?

author: mariush
author_rank: Super Contributor
timestamp: August 09, 2014, 01:49:40 pm
content: Could you add some dissipative coating, or some specially treated glass of some sorts?Not sure if this is something like this would help:http://www.intertronics.co.uk/products/ctec1755.htm

author: rob77
author_rank: Super Contributor
timestamp: August 09, 2014, 02:13:43 pm
content: i think it's not an ESD issue with those 1602 displays... i got the same behavior with poor decoupling and the very same when there was ringing through the supply rail in the circuit.just add enough decoupling caps - if you have a look at the cheap 1062 displays from china - you'll clearly see that there is not a single capacitor on the PCB

author: mcinque
author_rank: Unknown
timestamp: August 09, 2014, 05:05:37 pm
content: Thank you for the replies.Well, this LCD is from RS Components and it has the decoupling cap on the pcb. Howeveradding some decoupling to the LCD definitely improvesin airdischarge immunity.-----------About the CONTACT discharge immunity.By discharging the spark over the metal frame that holds phisically the display glass in place, I obtain the same scrambled chars on the display while the MCU keeps running normally.The LCD metal frame is of course grounded, so basically the energy should be clamped by the TVS placed on the power rail. I really don't understand where this energy injects itself in the LCD.Of course I must keep in mind that I'm using a >12KV electronic spark igniter and not an ESD gun (4KV for direct discharge), but I really wonder WHERE is going the spark to make the screen go crazy.I fear to probe what is happening to the power rail with my DSO(I mean, there is a lot of voltage in the sparks and DSOs are definitely fragile devices) and I don't have an high voltage probe to use or a long enough resistor that stops arcing, so...what do you suggest? The only thing that I've still not tried are an RC or LC filter on the power rail and ferrite beads... EDIT: also termination resistors...

author: dannyf
author_rank: Super Contributor
timestamp: August 09, 2014, 05:12:19 pm
content: Reset the lcd in the watchdog.

author: mcinque
author_rank: Unknown
timestamp: August 09, 2014, 05:26:54 pm
content: it's probably the best way, but since the MCU continues to run without any issues, it's hard to make it detect that any kind of trouble is happening, don't you?EDIT: I could try to force a LCD reset every X seconds, but the main problem is that I don't know how to do it; I'm using LiquidCrystal.cpp to drive the LCD, do you have advices?And since this device should count time, it's not practical to reset it every X seconds (the count will start over).

author: mariush
author_rank: Super Contributor
timestamp: August 09, 2014, 05:53:25 pm
content: You could power the LCD display from one of the IO pins - the lcd display itself (without backlight) only uses a few mA.Every few seconds, you could just turn off the whole lcd display for a few ms, then turn on the lcd display and initialize it again just as if your microcontroller starts for the very first time.

author: mcinque
author_rank: Unknown
timestamp: August 09, 2014, 06:14:44 pm
content: This is a nice idea!

author: SeanB
author_rank: Super Contributor
timestamp: August 09, 2014, 08:07:31 pm
content: If you are getting ESD to the frame simply ground it separately with a thick wire to the main ground, or the case if it is metal. The TVS does not work because of the inductance of the wiring to the display, you might want to add another directly to the display power pins as well.

author: mcinque
author_rank: Unknown
timestamp: August 09, 2014, 08:09:18 pm
content: Quote from: SeanB on August 09, 2014, 08:07:31 pmI will try it asap, thank you for the suggestion and the explaination because the TVS fails

author: calexanian
author_rank: Super Contributor
timestamp: August 10, 2014, 05:16:04 am
content: As it was said, blanking the LCD from time to time is good practice. The driver will drag all of the segments low and then re write your data. As fat as ESD, we had some issues about 20 years ago with the hitachi drivers, but not any since then. We find they are pretty good. LCD character module problems are typically of the reset, timing error, data buss, or general voltage level type. Remember, even thought the pinout is the same and the drivers are operationally standardized, they are not all truly equal.

author: SeanB
author_rank: Super Contributor
timestamp: August 10, 2014, 06:18:34 am
content: Just remember a lot of LCD modules are truly horrid in reset, you might find some that need to have the power off for a second or two ( or a short across the power rails for that time) to actually reset properly, and many take a second or more to restart before they either display anything or respond to commands.

author: coppice
author_rank: Super Contributor
timestamp: August 10, 2014, 11:06:02 am
content: Quote from: SeanB on August 10, 2014, 06:18:34 amMany LCD modules will function quite well with Vcc disconnected completely. The contrast might be a bit lower than normal, but it only takes one or two of the digital pins held high for the device to run. I once got really close to production before investigating the iffy contrast of the LCD, only to find Vcc wasn't connected. We went through all the software development, and beta testing of a few units, without any hiccup in the display's operation.

author: dannyf
author_rank: Super Contributor
timestamp: August 10, 2014, 11:07:28 am
content: QuoteBingo! ghost powering.

author: nuno
author_rank: Frequent Contributor
timestamp: August 12, 2014, 02:28:36 am
content: Quote from: mcinqueNot on all LCDs, check the end of this page for an example:http://elm-chan.org/docs/lcd/hd44780_e.html

author: mcinque
author_rank: Unknown
timestamp: August 12, 2014, 08:08:18 am
content: I've checked before by using an Ohmmeter

author: Andreas
author_rank: Super Contributor
timestamp: August 12, 2014, 10:32:12 am
content: Hello,is it possible to isolate the display in a way that makes direct ESD on the frame impossibe?(additional foil or glass)With best regardsAndreas

author: calexanian
author_rank: Super Contributor
timestamp: August 12, 2014, 06:08:04 pm
content: +1 for not all of the bezels are grounded on display modules. I have been bit by that one before!

author: sri5496
author_rank: Newbie
timestamp: March 17, 2015, 02:05:03 pm
content: Quote from: mcinque on August 12, 2014, 08:08:18 amhii have similar issueIn one of my projects i was using a 16X2 lcd display(http://uk.rs-online.com/web/p/lcd-monochrome-displays/7200207/?searchTerm=7200207&relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504E266C753D656E266D6D3D6D61746368616C6C26706D3D5E5C647B367D247C5E5C647B377D247C5E5C647B31307D2426706F3D313426736E3D592673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D3732303032303726) with atmega 328 micro, its failing in ESD test at 2kv and 4kv, its not resetting the micro controller but the screen goes gibberish, it seems like the data lines from micro or getting effected, it would be great if you guys can help me out for any possible fixes. can you let me know what fix u applied.thanks in advance.

author: SafaRR
author_rank: Newbie
timestamp: July 16, 2017, 08:18:59 am
content: Hi all;I have the same problem with 2x16 LCD. My device went to pass IEC standard for ESD immunity. But as operator move the 15KV ESD probe (as medical devices should immune to with respect to the standards) above the LCD, all the characters were vanished while the MCU and other parts of my device kept their functions correctly running. It seems that the LCD had some permanent damage. Because after re-powering the LCD it worked with some of its characters pale.Dose anybody have a solution better than continuous reseting of LCD?