HELP I got an old Accordion with Midi interface


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How come this didnt work then? :'(

Thats the adapter i used for the usb to midi to see if i got more power than the computers usb to actually power up the instrument.

Do you suggest its the actual midi2usb unit that reduces the current to my instrument and not the port itself?
 
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happyrat1

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Yup. The current limiting spec of the interface itself limited the available current on the 5 V pin.

The 220 Ohm resistor would do the same thing.

The circuit inside the accordion probably draws a good percentage of an amp. But your current measure inside the unit showed only 22 milliamps getting thru.

That's why they designed it with that "black box" power supply to feed a full amp or so to the circuit.

I think my earlier schematic with the resistor removed is a pretty good approximation of what that black box actually contained.

Gary ;)
 

happyrat1

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DO NOT hook it up to your computer's power supply.

1) It's a switching supply and will not operate without a rated load.

2) It is rated at about 200 WATTS of power which would easily smoke your accordion AND THE SUPPY if anything goes wrong.

If you want to test the circuit use 3 AA cells in series in a proper battery holder to test.

Gary ;)
 

happyrat1

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You need one of these cables


and one of these jacks.


Gary ;)
 
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Ok. I thought the pc power supply would be perfect though . Its 850w but i thought the 5v cables usually for leds n stuff maybe would be a safe output. Guess i will have to use a usb one like in the picture.
Couldnt i just hack it as it is (inside) instead of buying a coax to usb adapter?
Like taking the 5v and gnd from inside, directly to a jack?

Btw coax, did you mean a headphone jack or those things we used on old tv's for the antenna lol?
 
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You need one of these cables


and one of these jacks.


Gary ;)
I understand now! This should be possible.
I refuse to wait another week for more parts haha. I must have a look around the house tomorrow!

The closest thing i can think of that i have is
A usb cable like that, a charging cable for a tiny tiny drone i bought from china.
And the drone aslo has that same input.

Maybe its time to trash that drone;O


Oh and one of my headlamps is also charged with a cable like that.

Now i got some choices.



EDIT: just got answer from the accordion midi guy.

The external power supply was rated 1.25a
 
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happyrat1

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Be sure and check polarity when you wire it up and with Amazon one day prime you can have them delivered overnight :D

Gary ;)
 

tjw

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The 21.5 mA reading you show earlier is suspicious to me, I wonder how you connected the ammeter..... the reason I am suspicious is that @happyrat1 suggested you use a 220-ohm series resistor in the +5 volt lead. If the ammeter was applied in shunt to this, the calculated resulting current would be 22.7 mA.

Only a suspicion.... @happyrat1 is much more familiar with this and I'm glad he's helping you.

I think the reason it didn't work with your USB adapter is that "standard" USB-MIDI adapters are not constructed to apply power to the instrument. They simply connect the signal leads of pins 4 and 5 and perhaps a shield dran (if in their philosophy, this should come from the instrument and not the signal source). A good explanation from Sparkfun was passed along earlier in your thread about how "standard" MIDI is implemented.
 
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The first test using batteries.

3x aa in series.

I got a 4.7v reading and a 3a reading.

The display didnt fire up.

Im lost forever
 

happyrat1

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How are you measuring amps? Yo do realize you have to open the circuit and put the meter in series with it don't you?

Gary ;)
 
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I guess. Maybe not. But anyways it didnt work.
I had to google these batteries and should last at least for a while if it worked.m and provide enough current.

And i see the same thing with the display cables just like yesterday.

The voltage sent up to the display from the processors and the other stuff from the board inside is 1.5v.

And sure is a old old led type display.

What if just the system is broken or just wired up wrong.

At least nothing went into flames lol.

I tried connect midi cable too at the same time
With the 5v wire disconnected from the midi port ofc.
But nothing.

Too bad i didnt check inside the display when i had it opened. Then i could have googled some components inside.

Also i dont even know if the display is even supoosed to fire up before actually one of the buttons on it are assigned inside the computer software or sound module?

Maybe i just try it again and hook it up to the comp and see if i get any response.. could be a faulty display
 

happyrat1

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You can use a program called MIDIOX to see if there's any activity on the MIDI port when you press a key.

It's open source freeware and easy enough to find using google.

Gary ;)
 
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Yes. Already tried it with just the cable a few days ago. But since the midisystem didnt even power up, it showed up red inside the software
 
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Googled this. Looks like display operate at 2.5-3v
But the chips are at 5v. And a minimum of 4.75.

Soooooo i guess 4.7v didnt power it up then:oops:
 
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happyrat1

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Check if there's a ham radio club in your area.

Maybe one of those guys can help you out with this.

Otherwise I really can't think of anything else to try.

Gary ;)
 
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Im back!!! For more.
Hehe

I got some updates.

Just got in touch woth someone that do modern midi systems for accordion.

He told me that hes has done a few of these old types like mine, long ago.

IF he remembered correctly, he supposed it was a 12v 0.4a power supply.

Now this sounded a bit weird for me after i read through different spreadsheets for the chips thats supposed to have 5v.

He suggested that there must be some stepdowns anywhere on the board in the picture below.

Can someone try finding such a thing before i go mad enough to run 12v through this system?
 

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happyrat1

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He might be right. TTL voltage is 12 VDC. This would explain also why it has to be isolated from the external MIDI current loop.

Actually I would try a 9V adapter first. 9VDC is pretty common on FX Pedals in the music industry.

Look inside for a 7512 or 7505 regulator chip with a heatsink.

Gary ;)
 
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Nope. Cant find any regulators:(
But i found even more resistors mounted underside the board.

I got another reply saying that both pin 4 and pin 5 are for midi data.

Now, i removed pin 4 to use as power supply.
Doesnt that actually break the loop? Since it isnt going back into the cable?
 

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