I have a core which was a part of MB64 connected to a 2*16 LCD and eveything was working fine. This weekend I’ve tried to convert it to a MIOS compatible core, changed PIC and crystal, uploaded bootstrap 1.1b, MIOS 1.3 and AIN example 3 and it worked. Then I wanted to change LCD, connected 2*40 LCD and I can’t get it to show anything :-/ Core was still working fine, MIDI-OX recived pot and button changes like before. I’ve put back old 2*16 LCD and it’s working
2*40 LCD has an KS0066 controller which is compatible to HD44780 (as someone here on forum said), I’ve connected everything as it is drawn in datasheet so the only thing that comes to me is that the LCD is faulty
Any suggestions? Does anybody know how to test LCD ‘by hand’, without connecting it to the core module?
in theory you could test the LCD with a PC, the are several software drivers available in the web which get use of the parallel port. But using a core module should be easier.
Is this display working with a PIC16F?
Do you see a black line at the top all the screen (normaly the display will be initialized after the first level bootstrap loader phase has been finished - ca. 2 seconds after reset
Which return value is sent by MIOS with following SysEx request string:
Thank you Thorsten for fast response. After some extensive soldering/desoldering (wasn’t able to get pfosten thing) I’ve found out couple of things
2*40 is working but the working dots are so pale that it’s almost imposible to see them ie. I can see what is written on LCD but I have to stare at angle almost parallel to LCD surface. I get the same results regardles of contrast/luminance settings. Also it’s same with PIC16F and PIC18F (I do get a black line at the top during initialization), I even tried LCD with old MIDIbox Plus - same results
I’ve sent the sysex and got the proper response F0 00 00 7E 40 00 0F 00 02 F7
Things got little bit stranger. I’ve connected 6.5V directly to J2 on the core, bypassing voltage regulator and to my surprise the LCD is working perfectly, everthying on it can be seen clearly, also every pot and every button is working
I’m wondering, maybe this LCD needs negative voltage at V0 as I read some LCDs do need -7.5V. In that case difference between Vd and V0 would be 5V - (-7.5)=12.5V which is closer to 6.5V then 5-0=5V (which is now the best case, goes to 5V-5V = 0 when I turn contrast pot all the way up).
Does this sound logical enough to try to make -7.5V power supply? Or the LCD has another kind of problem?
7805 doesn’t get any hotter then with 2*16 display.
It seems that I wasn’t precise enough. When I said pale I meant dots - I can see ‘Received a DIN Event’ but dots which are supposed to be black are too pale, almost impossible to see. Backlight, on the other hand, works fine
And I’ve plugged regulated 6.5V after the 7805 (which in this case does not regulate anything), meaning that the PIC18F, 6N138, LCD, 4051, 74HC165 and everthying else is working on 6.5V. And if I keep contrast pot to the minimum, V0 is 0V so the difference Vd - V0 is 6.5V
There are some LCDs which are working with a different way to control contrast and lumen. Best would be that you get the datasheet of that LCD and look the way, they suggest to control the contrast.
But if you got it to work, does that matter? Hey, it works, doesnt it? Cool. ;D
However, I would *not* power a 7805 the wrong way and I also would *not* power those PICs with a to high voltage. You could burn some of those chips. :-/
I’ve looked through the datasheet and found nothing about controling contrast. Only thing is that they suggest 0.3V on V0 which then gives absolutely unreadable characters. Frying PIC is also my concern so I’m giving a go to 7905 to try with -5V. Hope that works but if it doesn’t then external supply it will be
The originator of this circuit is Douglas Pederick.
Note: what he calls “HD44780” is the display which requires negative voltage, so in your case the KS0066 - the required V0 voltage of a LCD module is independent from the controller.
For the records: graphical LCDs require also a negative voltage, but -10V or lower. A solution for such displays can be found under Concepts->MBHP->LCD
Negative voltage on pin 3 is the solution. Â I’ve tried with the 1.5V Â battery, with ‘+’ connected to GND and ‘-’ to V0 on LCD and contrast is just perfect now, everything is readable.
I’m not using AC so I searched for DC-DC solution and I’m gonna try Maxim MAX1044 voltage inverter. It has option to invert +5V to -5V with using only 3 other components (electolytic caps). It’s the most simple DC solution I stumbled across with enough mA, also the PCB will be miniature
