Can someone help me out with MB-6582 LCD displays?

[jaytee]

I've read all the relevant documentation that I could find on LCD character displays—mostly this, this, this, and this, along with various sections of the MB SID documentation and dozens of forum posts—and I'm still left with a few questions...

First off, where I am in my project. Questions are down below. I have my MB-6582 power section fully built. I went ahead and built all four cores (I was going to do one at a time, but after you solder in all the resistors, capacitors under sockets, sockets themselves, and headers, there's only like three more components per core to add). I checked all my voltages and everything checks out. I inserted my first PIC and successfully uploaded MIOS (though not the SID application yet). So everything seems good so far.

I haven't ordered my 20x4 LCD yet (more on that later), but I have a 16x2 LCD handy (this one) and figured I would use that to test while I wait on more parts. The MB SID manual says that 16x2 is supported, just not recommended because of its size. I read the above documentation, get a cable all ready, connect it to the LCD, and...nothing. Fiddling with the contrast trimmer and the cabling, I manage to get a few weird things to display, but nothing that indicates things are hooked up properly.

Now, I strongly suspect that it's either a mechanical issue with my connection (its hooked up somewhat haphazardly through a breadboard, rather than soldered) or a mix up with pin connections. But! before I go chasing phantom soldering issues, I am hoping to clear up a few questions I have, just to rule stuff out and gain a better understanding of how everything works.

HERE ARE MY QUESTIONS

First, does anything need to be changed in the code to support a given size of LCD? Like right now, I just have basic MIOS installed on my PIC, v1.9 as available as the top download link on this page; should I expect it to display startup information on any size (2x16 or 20x4, for instance) of standard LCD, or do I need to tell it what size to expect somehow? How about once I install the MB SID app?

Second, 4-bit mode and 8-bit mode. My understanding is that the MB SID app wants to run LCDs in 4-bit mode. Some documentation indicates that a special cable wiring setup is required for this (seen here), but while trawling the forums for information, a lot of folks suggest not to worry about special wiring. Not really sure what's what here.

Third, can anyone offer a wee bit of guidance wrt choosing an LCD? I was looking at Crystalfontz and this LCD looks particularly striking. Green on black! Looking at the specs, I'm 99.9% confident that this part is compatible with the MB-6582. Only thing holding me back is the price: $25 once you add shipping. Meanwhile, there are 20x4 LCDs from China on eBay for like $6. I understand that you get what you pay for, but I'm wondering if anyone can comment on where that extra $20 goes on a Crystalfontz. Nicer colors? Less likely to break? Better contrast? More responsive? All of the above?

Last, my backlight trimmer doesn't seem to affect anything. Backlight is on and at constant brightness no matter how this trimmer is set. I think I'm missing something obvious here.

 

Now, like I said, I understand that the simplest explanation is that I just don't have things hooked up securely or properly. I just figured this would be a good chance to stop and ask some questions that were bothering me (and probably only still bother me because things didn't work on the first try).

[Smithy]

IIRC if you flash the MIDIBOX sid firmware file it is set to work with a 2 line character display.

And if you flash the mb-6582 firmware it is set to work with a 4 line character display. 

This is way of getting around having to edit code.

 

if you want to code it yourself reference this page, and scroll down:

http://wiki.midibox.org/doku.php?id=lcd

The crystal fonts displays should provide better constrast and viewing angles to el cheapo lcd displays.

 

As for wiring Im pretty sure Ive my displays wired up for 4-bit, just try that first and if it works great!

I wouldnt hesitate any further in ordering and installing a display.

 

[latigid on]

You can change for 8-bit by closing solder jumpers on the PCB:

 

As for LCDs: don't be such a cheapass! The price and availability of these has come down hugely over the years. I would even go a step further and look at installing an OLED, just make sure it can handle +5V logic. Also ensure the mechanical fit works with the mounting holes/cutout on the CS PCB. Usually these things are pretty standard, but you can never be too sure.

 

[jaytee]

3 hours ago, latigid on said:

As for LCDs: don't be such a cheapass! The price and availability of these has come down hugely over the years. I would even go a step further and look at installing an OLED, just make sure it can handle +5V logic. Also ensure the mechanical fit works with the mounting holes/cutout on the CS PCB. Usually these things are pretty standard, but you can never be too sure.

I actually looked into OLEDs, but was mostly put off by the fact that the MB-6582 is built specifically for LCDs in terms of depth. Seems like an OLED will be really sunken in or require a bit of jiggery to mount it on top of the CS PCB. I am curious if that Crystalfontz I linked to will look as nice in person as it does in the picture.  It's got beautiful contrast and almost looks like an OLED. I am skeptical, but otoh, their other photos of their LCDs look pretty much how I'd expect LCDs to look...

Regarding soldering jumpers for 8-bit mode. I saw and read through that thread, but I am still left not really understanding the *why* of it all. It seems like some folks leave the MB-6582 in 4-bit mode but build the LCD cables according to 8-bit mode instructions and things turn out fine.

 

11 hours ago, Smithy said:

IIRC if you flash the MIDIBOX sid firmware file it is set to work with a 2 line character display.

And if you flash the mb-6582 firmware it is set to work with a 4 line character display. 

This is way of getting around having to edit code.

That still leaves me wondering if anything needs to be adjusted for using a 16x2 instead of the standard 20x2? Will the 16x2 automatically truncate those last 8 characters, or do I need to change the firmware to adjust for the smaller test display? I haven't even uploaded the MB SID app yet, just vanilla MIOS.

[Hawkeye]

Short answers:

yes, you can use the 16x2 LCD to try it out, no adjustments necessary, the lines will be truncated, otherwise no harm will be done. Of course you won't see all information, but it is good to test it.

OLEDs are indeed partially tricky with the MB6582, because of 4/8 bit addressing mode and timing issues. I once hacked an Electronic Assembly OLED to be compatible, but it was no easy task, also i managed to burn it up afterwards (either it was not 5V capable as Andy pointed out, or i made some other late-night-mistake ;-)). There might be newer OLEDs without those compatibility issues, but there is a longer thread on here, where multiple guys tried to get OLEDs up and running and it was a non-trivial task. Besides than that, the height of the display is no problem, it will fit nicely.

Third, definitely solder the connection, i would not recommend breadboarding, here is a description on how to map the cables:

Good luck and many greets!

Peter

[jaytee]

Already have your CS thread bookmarked! ;) It's one of the best pieces of documentation for the MB-6582 around (and I almost never found it because it's hidden in some other forum!). I'm 90% sure I got the cable mapping right (using both your guide and my datasheet), but I'll double check as I solder it.

[jaytee]

Ok, took it out of the breadboard, soldered everything up, double checked my connections, fired it up....nothing. U solder some wires to try out 4-bit mode, nothing. But at least now it's a consistent nothing rather than constantly changing gibberish, which indicates to me that the breadboard *was* an issue, just not the only issue.

 

So the "nothing" I'm getting is two full lines of completely blacked out characters. Contrast knob does nothing. Backlight turns on fine, but as before, brightness knob does nothing. Checked the input voltages and they come out to 5V as expected. Not sure where else to start checking.

any ideas?

 

edit: just found the LCD connection test app. trying it now...

double edit: I ran the app, everything checked out, felt *really* stumped, then realized I've have it connected backwards the entire time somehow, even though I double and triple checked before hooking it up every single time. WTF.

Edited January 25, 2017 by jaytee

[jaytee]

Success! (Though my brightness knob still doesn't seem to do anything...)

 

 

[jaytee]

So any ideas about my backlight brightness/luminance?

I checked that the trimmer was working, and it is; voltage varies between 0-5V as it is turned. But by the time those lines make it to my LCD, it's a constant 5V no matter what. I'm not totally clear on what the little circuit near the trimmer does, with the transistor and resistors, but it seems to be the problem. Is it possible I burned out my BC337 while soldering it in?

Edited January 26, 2017 by jaytee

[yogi]

21 hours ago, jaytee said:

Ok, took it out of the breadboard, soldered everything up, double checked my connections, fired it up....nothing. U solder some wires to try out 4-bit mode, nothing. But at least now it's a consistent nothing rather than constantly changing gibberish, which indicates to me that the breadboard *was* an issue, just not the only issue.

 

So the "nothing" I'm getting is two full lines of completely blacked out characters. Contrast knob does nothing. Backlight turns on fine, but as before, brightness knob does nothing. Checked the input voltages and they come out to 5V as expected. Not sure where else to start checking.

any ideas?

 

edit: just found the LCD connection test app. trying it now...

double edit: I ran the app, everything checked out, felt *really* stumped, then realized I've have it connected backwards the entire time somehow, even though I double and triple checked before hooking it up every single time. WTF.

As I was reading your posts , first thought was 'it's connected backwards' - because I have done the same thing and puzzled for days why the contrast didn't work :) Glad you got it straightened out!

About the Brightness, it could be that the LCD doesn't respond to any current changes, I have a blue display that works this way. Other LCDs plugged in work fine but that one just has fixed brightest. I would say to not mess with the bias circuit till you can try a different LCD, I wasted time doing the same thing only to find out is was the display.

Yogi

EDIT: the Bright bias circuit only adjusts the current level, the line will always be at +5V. If you really want to test, you'll need to attach a load, R about 1K would be OK, and have your meter inline set to mAs. Don't know the range of the circuit but assume it's only about 10 mA.

OR you could try a LED across the pins B+ & B-, should see it dim/brighten

 

Edited January 26, 2017 by yogi

[jaytee]

Thanks! I had a vague suspicion it was just the LCD—the datasheet doesn't mention brightness control at least—but couldn't find any other references to that being a possibility, so I immediately jumped to user error.

I tried your LED test real quick and...hmmmm. It actually causes the brightness of the screen to work...somewhat (limited range). In any case, I won't mess with it until I have my final display hooked up; this one is just for testing.

[Hawkeye]

Congratulations! Getting the display (any display) running is the first step to MB6582 addiction, now wait until you hear all 8 SIDs in unison! :-)

Have a great weekend!
Peter