First post!
I’m retrofitting a piano to be MIDI controlled and have limited electrical circuit knowledge a but willingness to learn and scour the internet for info.
I bought a MIDI processor that contains eleven (11) 18 pin ULN2803As to drive 88 separate solenoids for each piano key. The solenoids have a 44Ω coil and perform the required task at 12-15Vs. The MIDI processor has two voltage inputs, 5V to run the MIDI decoder and another one for a higher voltage of the users choice to push the solenoids.
From what I can gather the ULN2803A can handle 500ma for one line but using 12 -15V and pushing 250 - 350ma through 4,5,or 6 lines at one time will fry it.
Sooo…I decided to push 5V through the ULN2803A and let a TIP122 do the heavy lifting to the higher voltage.
Please comment if any of the above content requires feedback so far.
The problem is that the MIDI processor appears to be routing the -5V through the switched transistor array and the last pin is the common positive. All of the wiring diagrams I’ve come across show it opposite.
My web search skills have taken as far as they can and now I am reaching out for help. Attached below is my incomplete schematic for someone smarter than me to provide the solution. Please take a look and provide feedback.
I’m retrofitting a piano to be MIDI controlled and have limited electrical circuit knowledge a but willingness to learn and scour the internet for info.
I bought a MIDI processor that contains eleven (11) 18 pin ULN2803As to drive 88 separate solenoids for each piano key. The solenoids have a 44Ω coil and perform the required task at 12-15Vs. The MIDI processor has two voltage inputs, 5V to run the MIDI decoder and another one for a higher voltage of the users choice to push the solenoids.
From what I can gather the ULN2803A can handle 500ma for one line but using 12 -15V and pushing 250 - 350ma through 4,5,or 6 lines at one time will fry it.
Sooo…I decided to push 5V through the ULN2803A and let a TIP122 do the heavy lifting to the higher voltage.
Please comment if any of the above content requires feedback so far.
The problem is that the MIDI processor appears to be routing the -5V through the switched transistor array and the last pin is the common positive. All of the wiring diagrams I’ve come across show it opposite.
My web search skills have taken as far as they can and now I am reaching out for help. Attached below is my incomplete schematic for someone smarter than me to provide the solution. Please take a look and provide feedback.
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