How to use teensy 4.1 and interface with a 5v synth?


Hi All,

I am very new to Teensy. I am wanting to use Teensy to add MIDI functionality to a 5v pre-MIDI synthesizer. That synth runs on 5v.

The research I had done pointed me to the Teensy++2.0, as it was 5v native. I chose the 2.0++ as I need 30 inputs to interface with the synth I am wanting to convert (via teensy) to MIDI.

Now I discover the 2.0++ boards are either no longer available, or very expensive. The 2.0 boards are readily available, but do not have the 30 inputs I need.

I would be happy to use a 4.1, but they run on 3.3v and the synth runs on 5v. I understand there is a way to "step up" the voltage from 3.3v to 5.v, but I just do not understand the technical language to know what I need to purchase or how to wire it into the Teensy 4.1 to achieve a 5v output.

I searched the forum, but get what feels like a 100 hits, none of which I read through address my question in a way I can begin to understand. I am also not sure I am asking the search question correctly to get the answer I need.

Can anyone point me to an article or link to clear this up?

Much appreciated!
What exactly should be controlled in the synth: Will you receive or send signals? Analog or digital?

For digital signals you could use available boards with level shifters.

For analog signals going to the input of the Teensy: voltage dividers with resistors could be a solution.
I am planning to control the keyboard and control panel matrices. The attachment's show a legacy MIDI converter for the SK-1 synth from the 1980's. This board was only for the keyboard matrix. I am wanting to use the Teensy in place of this legacy converter and use the same process to also gain access to the SK-1's control panel matrix. This 1980's board was sold for a period of time, so it was successfully applied.

It looks digital to me (?). And it is all output at 5v.

I attached 2 images from the 1980 project write up that may help.


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I replied but I believe I replied to the group - not to you specifically. Could you take a look at the thread?
Snuffling around the Matrix, thinking out loud:-

Table at the bottom of page 7 of the service manual looks to me like the whole thing is addressed with a 10x8 matrix so am thinking that 18 mcu pins might do the trick. Looks feasible with a T2.0 and being a +5v mcu, bypasses any need for level shifting. As for mcu speed, the original Midi kludge kit used a member of the 8051 family running at 12 Mhz, The T2.0 is a little faster at 16Mhz so I don't think will have trouble replacing the 8051.

Meditating a little more on the schematic wrt the Normal/Solo1/Solo2/Chord switch, think of it as a single-pole four position switch, and, the PowerOff/Play/Record switch as a Double-Pole three position switch.

Speaking of power, Page 12 suggests that VA (5V) is always enabled even if APO (AutoPowerOff) has kicked in. I'd imagine that we don't wanna break the bank of VA's current capacity by pulling too much to power our new Midi Kludge kit. Be nice to wake up the Casio via Midi.

Perhaps a T4.x is a 600 Ton Excavator used as a flyswat here. Thinking that a bare bones 328 can be made to work without compromising VA. A T2.0 (324) may need some peripherals turned off to reduce power consumption.

This project tickles my fancy, had loads of fun with one back in the day..
Those old 8051 chips effectively divided their clock by 12, where most instructions took 12 or 24 cycles. So an 8751 chip running at 12 MHz would have performance comparable to AVR at 1 MHz, where most instructions take 1, 2 or 3 cycles.

So yes, would agree pretty much any 1990s era AVR chip ought to be able to do this, with careful programming (8051s were usually programmed in assembly).