Changes in Midibox Plus schematic

[Guest Matthias]

Hi Midibox Forum,

I once built a MidiBox (Plus) 16 an have not yet had the time to do finish the work on it for more than one year(maybe even two years). Coming back to www.ucapps.de, I see the changes Thorsten made to the schematic. Some will not be easy to realize on the narrow vectorboard layout I use, but which do I have to if I want to use the newest software version?

Which optocoupler I use (CNY17-II or 6N138) will make no difference, I guess.

(by the way: which were the problems users reported with the CNY17-II?)

The additional wire between Pin 23 of the PIC and the R/W input is no problem, as well.

The diodes to the buttons will only be necessary if I intend to press more than one button at a time, so if I do so and get the known feedback effect, I will surely be reminded...

The MIDI-In-LED also isn't a must, as wasn't even the MIDI-Out LED when I started building my box.

But there are other changes made to the schematic that are not documentated. If these improve the quality of the box or make it run more stable, I would surely like to implement them. These are: 100 Ohm resistor between +5V and Pin 1 of the PIC, the missing links from pins 4 and 5 to +5V and ground, +5V through 1k resistor to pin 6, no more pin 7 to ground connection, and both capacitors between pins 31 and 32 are missing. These bars labeled J01 to J13 surely only signify connection panels.

Now: Which of these changes improve the quality and stability of my MIDIbox? Which do also work with software version 1.909 or 1.908(I think that's mine)? If I update to 1.910, which hardware changes do I have to make in order for the Midibox to work properly?

One last question: Does it make no difference whether I use the 16F874 or thr 16F877 PIC - apart from the 77's ability to store more snapshots?

Thank you for your help.

Matthias S.

[TK.]

Hi Matthias,

the undocumented changes are changes which have been made before firmware v1.910 to avoid questions like "why do I see this or that component in the MBHP core schematic, but not in the MIDIbox Plus schematic?"... it's just to keep it consistent... now I'm surprised that they are confusing users who already built a MIDIbox Plus --- you only need to take care for the documented changes, believe me! ;-)

In fact you only need to add the RD# line to the LCD to get v1.910 running on your older MIDIbox variant.

• you don't need to change the optocoupler. The CNY17-II is a low-quality optocoupler, the manufacturers don't guarantee that the same pull-up resistors are working - in fact most users noticed no problems, but some were not able to get the CNY17-II running. No problems anymore with the 6N138 - so no issue
  
• 100 Ohm resistor: just a suggestion by Microchip, but not really required - with this resistor it's easier to add a reset-button - so no issue
  
• Pin 4 and 5 are not tied to Vcc/Vss since the firmware doesn't use them as voltage reference anymore (due to layout reasons). It doesn't matter if you connect these pins or not - so no issue
  
• the 1k pull-up at pin 6 is for users who want to use the  MB1664 variant and don't read the README before trying out the firmware - it's not required if you don't use the MB1664 firmware, so no issue
  
• pin 7 never was connected to ground
  
• the capacitors between pin 31 and 32 can now be found at the bottom (C3/C4)
  
• the MIDIbox Plus firmware doesn't make any additional difference between PIC16F874 and PIC16F877 beside of the snapshots storage
  

Best Regards, Thorsten.

[Guest Matthias]

Hey, thank you very much, Thorsten, that was a quick reply! Hope I'll get my MIDIBox completed soon - at last, I don't only want to build it, but also use it.

Thanx again

Matthias