Some changes to schematics (original "I screwed up")

[dmitri]

I think I've managed to solve the problem:

In MegaDrum32 Digital board: R26 - from 220 to 4k7 (thanks to Synthex for the suggestion)
In MegaDrum8 Digital board: R21 - from 220 to 4k7
In AVR-CDC USB board: R4 - from 470 to 1k
In PIC18F2550 USB board: R4 - from 470 to 1k

After these changes Sysex doesn't cause any problems anymore, at least on my dev board. Both Synthex's MIDI USB and AVR-CDC work fine for me.

[estregan]

I think I've managed to solve the problem:

In MegaDrum32 Digital board: R26 - from 220 to 4k7 (thanks to Synthex for the suggestion)
In MegaDrum8 Digital board: R21 - from 220 to 4k7
In AVR-CDC USB board: R4 - from 470 to 1k
In PIC18F2550 USB board: R4 - from 470 to 1k

After these changes Sysex doesn't cause any problems anymore, at least on my dev board. Both Synthex's MIDI USB and AVR-CDC work fine for me.

Ok. I will try this and report back my progress. Thanks!

[Synthex]

In MegaDrum32 Digital board: R26 - from 220 to 4k7 (thanks to Synthex for the suggestion)

I had made the "correction" some days ago, following a somewhat similar problem of communication with the USB interface.
Sorry not to have reported earlier
All's well that ended well

[TriggerThis]

I was asking myself if I should modify the desing before making my board.

I've made a couple of MIDI devices over the years and I never seen a 6N138 connected the way you did. Most circuit I've seen did not have R25 and would have R26 with a value of 2.2K.

If I had to make my MegaDrum with the USB board, I would modify the circuit with R26 at 2.2K (or more) and add 2 buffers made up of a 5400 (2 NAND gates in series). One buffer replacing R25, and another buffer going from pin 5 of the USB ext.1 connector to pin 14 of the Atmega32.

This way, there would not be problems with having the USB board and the 6N138 connected together to pin 14 of the Atmega32.

It would add one 14 pins IC to the board though.

Does this make any sense ? Or am I horribly wrong ?

[Synthex]

When I had my problem of communication between the USB interface and the Atmega32, I thought put a 74LS04 as a buffer on the TX and RX line. But the simplest solution was to increase the value of R26 (on MegaDrum32).

R25 is necessary because we have two interface (USB and MIDI) on the same Atmega32 bus.

So you are in the true, but I do not think it is really necessary.

[Synthex]

One buffer replacing R25, and another buffer going from pin 5 of the USB ext.1 connector to pin 14 of the Atmega32.

You can not do that, because if one is to '1' and the other to '0', it makes "boom"
You must add resistors in this case ! (for example : R25 )

[estregan]

I've tried your correction re the R26 resistor on digital board along with the resistor change on AVR-CDC board. I get no "buffer overflow" errors now but I have a new problem.

Now I get constant midi signals from almost all inputs. I also installed buttons and an LCD and the new resistor and LED addition to see what's going on with megadrum. Upon powering the unit, the LCD already displays channel 21 AuxR and I can't change the channels. I read somewhere in the forums that there should be a setup screen upon powering up but I can't find that.

What do you think is wrong with my unit? I'm going to try to create a new digital board, but in the meantime that I haven't done that, do you have any ideas?

[dmitri]

I've tried your correction re the R26 resistor on digital board along with the resistor change on AVR-CDC board. I get no "buffer overflow" errors now but I have a new problem.

Now I get constant midi signals from almost all inputs. I also installed buttons and an LCD and the new resistor and LED addition to see what's going on with megadrum. Upon powering the unit, the LCD already displays channel 21 AuxR and I can't change the channels. I read somewhere in the forums that there should be a setup screen upon powering up but I can't find that.

What do you think is wrong with my unit? I'm going to try to create a new digital board, but in the meantime that I haven't done that, do you have any ideas?

1) Do think you might have accidentally applied settings from MegaDrum Controller with too low threshold/high gains? See this in the last Changelog, as the first step it may help:

Changes in 20071124 version:
1. Skip 'Autoload Conf' if the key 'RIGHT' is pressed during powering up.
...

2) Do you have a HiHat controller(pedal) connected? If no, then MegaDrum will think that the pedal is pressed all the time. With the pedal pressed, hitting a pad will jump to this pad in the menu ( for quick navigation around menu). If a threshold set too low and/or gain set too high for a single/several channels these channels will falsely generate pad hits and with the hihat padal pressed it will constantly jump between channels in the menu or will be stuck in one of the channels.
You can either connect HiHat pedal and than manually set threshold/gains on the channels generating false hits, or you can try to first 'Get Settings' from MegaDrum and then 'Apply Settings' after setting thresholds higher.

[estregan]

1) Do think you might have accidentally applied settings from MegaDrum Controller with too low threshold/high gains? See this in the last Changelog, as the first step it may help:

Changes in 20071124 version:
1. Skip 'Autoload Conf' if the key 'RIGHT' is pressed during powering up.
...

2) Do you have a HiHat controller(pedal) connected? If no, then MegaDrum will think that the pedal is pressed all the time. With the pedal pressed, hitting a pad will jump to this pad in the menu ( for quick navigation around menu). If a threshold set too low and/or gain set too high for a single/several channels these channels will falsely generate pad hits and with the hihat padal pressed it will constantly jump between channels in the menu or will be stuck in one of the channels.
You can either connect HiHat pedal and than manually set threshold/gains on the channels generating false hits, or you can try to first 'Get Settings' from MegaDrum and then 'Apply Settings' after setting thresholds higher.

I just tried these suggestions and it worked wonders! I now go to tweak the settings to better adapt to my diy kit! If all goes well, a video will be coming soon.

Thanks a lot!

[TriggerThis]

I think I may have found a little problem with the MIDI IN connection in the schematics.

Pin 2 of the MIDI IN jack should not be connected to ground according to numerous MIDI documents I have. Also, when I look at the schematics of all the MIDI equipement I have here, including Roland's Octapad II schematics, none of them have PIN 2 of the MIDI IN connected to ground.

Seems it has to be done like that in order to prevent ground loops ... thats also why there is an opto-isolator at the MIDI input.