New build issue: HM v4.3 LCD problems


 
M

Marcin Szczepanski

New member
Hey folks,

I’ve just built my v4.3 HeaterMeter kit and have an issue that doesn’t seem totally uncommon from some of the posts I’ve found - the LCD isn’t working. However I wouldn't be posting this if I found a solution there :)

Everything else seems to work just fine, probes, web UI, buttons and LEDs. Setting the backlight %age in the UI changes the backlight. If I turn the contrast down quite a bit I get lines that occasionally shift around but definitely nothing that looks like text. I've tried with power from the Raspberry Pi (it's a Zero W if that makes a difference), 12V power from the barrel jack, as well as with and without the Pi connected.

The LEDs work, including the “lid open” light and I can toggle that with the left button, so as far as I am aware that means everything up to the shift register should be OK as the lid open uses SPI as well? In any case, I’ve checked all the continuity from the LCD all the way to the ATMEGA / Raspberry Pi (as per this comment here: https://tvwbb.com/showthread.php?70...ng-lcd-display&p=836543&viewfull=1#post836543)

I’ve checked there’s no continuity between unexpected pins on the LCD module itself, and checked voltages too and everything seems to be correct as per this comment (https://tvwbb.com/showthread.php?40521-Another-problem-with-the-lcd&p=415316&viewfull=1#post415316)

Is it possible that it’s a defective LCD panel, or I’ve somehow fried it? I did initially have a cold solder on the contrast pot so the voltage between pins 1 and 3 was reading 5v, but I’ve fixed that - I’ve even tried adjusting the pot while reading voltage to get it as close to 1.4v as possible.

A friend is lending me his logic analyzer this weekend, so I’m going to try and hook it up to the header on the other side of the LCD and verify the data patterns look OK based on the LCD datasheet. I guess if that all checks out then it’s just a dead LCD module?

I have one of these LCDs lying around from my Arduino starter kit: https://www.winstar.com.tw/products/character-lcd-display-module/dot-matrix-lcd.html - a quick scan of the datasheet compared to the Newhaven one looks like it should be compatible, so if I have to desolder the Newhaven one I can try this one.

Would definitely like to eliminate all the possibilities before I start desoldering the LCD to replace it. Any ideas of something worth trying that I could’ve missed?
 
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So, it was definitely the LCD module. I got my friend's logic analyzer and there seemed to be correct looking digital stuff on all the right pins (as compared to my other LCD module on a simple Arduino test rig). So it was time to desolder.

I haven't done any serious desoldering before - and the "header sandwich" of the LCD made it tricky to remove all the solder (at least with the tools at my disposal - a solder sucker and solder wick - a hot air gun, or desoldering gun would've come in handy!). After a frustrating few hours trying to cleanly desolder the LCD I finally got it off, though with a bit of brute force and damage to the PCB unfortunately (as well as melting a button a bit with the iron). However, after cleaning things up, patching one missing pad :(, and getting a new header on I was able to get the LCD I got with my Arduino kit plugged in and success! Everything worked. I haven't been able to get the Newhaven working properly in my test rig either. I guess at this point it's hard to tell if it was DoA or something I did to it during assembly.

ddHdclz.jpg


Now I have a dilemma - the HeaterMeter is designed for the Newhaven module, which seems (from my searches) to be relatively unique in having a header on the top and bottom sides of the LCD. Most generic 16x2 modules have the header at the top only, which is not the one used by the HM. The only places I found the same Newhaven module were Mouser and Digikey, both of which charge more than the cost of the module to ship it to Australia. I haven't been able to find a local source for a "bottom header" LCD (though my search hasn't yet been exhaustive).

I currently have the LCD temporarily connected via some jumper leads - so either I a) put in some sort of shim / board to make that more permanent and be able to use the board with a "top header" LCD, b) I buy some other parts from Digikey/Mouser I don't _really_ need right now just to get free shipping :), or c) buy another LCD/parts kit from the HM store which isn't much more than the minimum Digikey/Mouser free shipping order.

At this stage I'll probably just stick to option a) - at some point the need to buy more stuff will come up and I'll have a minimum order.

In any case, I'm happy - everything works. Now the fun of going through the options of attaching the blower to my WSM begins...
 
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Marcin Szczepanski said:
c) buy another LCD/parts kit from the HM store which isn't much more than the minimum Digikey/Mouser free shipping order.
Click to expand...
Oof that stinks about the LCD. They should be tested at the NewHaven factory, but I've seen one bad LCD right out of the box (one side was impossibly dim) so I'm sure some bad ones sneak in. I think yours would be the third that was bad out of the box, which isn't too terrible odds I suppose considered the (three) thousands of HeaterMeter out there.

If you can just limp along with that Arduino LCD for now, I can send you out a new LCD/Button board with all the parts needed to make a complete new half. Just verify that the address you want it sent to is the same as in your order, or email me at heatermeter@capnbry.net if you want to make a change. If I don't hear anything it will go out tomorrow about noon UTC-4 I'll just go with the address from your order.
 
Thanks again Bryan, I couldn't even wait to get the buttons on to try it out:

seQEzHQl.jpg


Success!

Finished it off, and put it all together, and it's working great.

hPfdQ4Ll.jpg


Only thing I had to do was drill out the probe holes slightly in the printed case (self-printed), the Thermoworks collar is too fat and the socket is too far in, so it doesn't make a good connection (as you can see in the photo the probe isn't registering because it's pushed out. Anyhow, working nicely with the deeper holes, and I already tried the rest with the temporary LCD on the weekend, but looking forward to the next cook with everything held together properly!

Thanks again for the replacement button board kit, and for a great project!
 
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