Convert 0-5V logic to another range

[tonewill]

Hello, I wonder if someone can help please:
First, my electronics knowledge is not great, so please bear that in mind.

I want to convert a 0-5V logic signal to a short -14-0V pulse. I have access to a -14V power rail.

In case that isn't clear, I have a highly liquid MD24 that converts MIDI note off/on signals to a logic 0-5V signal. It stays at 5V for as long as the note is held, but I want just a short pulse each time a note is played, and at a different voltage range.

I do not know the exact length the pulse should be, I can experiment but it's just a trigger pulse so let's say, I don't know, a few milliseconds.

I have some transistors, caps and resistors here to play with.

I appreciate any help,
Many thanks.

[Uncle Krunkus]

Someone might jump in and correct me here, (I'm just going with a gut feeling) or at least tweak my idea a bit. Feel free.
But,...
I think you want a PNP transistor (2N3906 comes to mind, or something similar)
The collector goes straight to the 0V line.
Your input comes through a resistor (10K?) into the base.
The emitter goes through another resistor (10K?) to the -14V line.
Off the junction of the emitter and resistor, connect another resistor (2K?)
After the 2K output resistor, put a cap (330nF?) to the -14V line, and the output comes off the junction between the 2K and the 330nF cap.

It may not be exactly right, but that's what I'd start playing with on the breadboard to get started.

It'll be interesting to see how far out I am on this idea. Hopefully we'll both learn something.

[tonewill]

Thanks very much! I just happen to have a few 3906s here. I've attached a picture of my breadboard just to show that I am trying this .

I haven't connected anything to the input yet, I wanted to make sure that it didn't interfere with the drum machines internal triggers first and I need to disable the MIDI converter from another project.

I measured some constant voltage between the output and -14V and between the output and 0V. One was around 5-6V the other around 8V.

Will dig out the MIDI to gate converter now and post my results.

Thanks again.

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[elmegil]

I think the way uncle describes it, that would end up being normally -14 with a pulse going up to gnd.

I would arrange the PNP such that the resistor was connected to the collector side, and you take the output (into the cap to generate a pulse) from the junction of the resistor and the transistor. That way you're normally connected to ground (when the transistor is cut off) and then go negative when you get the gate in to the base.

The other stuff to make a pulse out of a gate sounds right but I haven't thought about it very far at this moment.

I'm assuming you have the MIDI -> gate part already worked out, and that's what's feeding the base of the PNP. Edit: duh, need to read the entire thread, of course you have that taken care of


Edit 2: the more I think about it the more I think maybe we have current flowing the wrong way here too. Maybe should be the way he described except -14 on collector and gnd after resistor from emitter.

Might be useful to simulat it here: http://www.falstad.com/circuit/

[tonewill]

Thanks elmegil:

[elmegil]

Sorry, I misunderstood that part....

[tonewill]

I connected one side of a micro-switch to 0V, the other side to a 100n capacitor and a 100k resistor. The other side of the resistor I connected to -14V (pull-up or down, you tell me!) and the other side of the capacitor I connected to each sound trigger input one by one and tested by pressing the switch. This triggers the sounds beautifully and as they should be.

Converting the 5V logic didn't work at all for me, not sure why. Anyway, I'm going to have to leave it for now and look at it again later.

Thanks for all your help chaps.