Switching pulse? Comparator? 555?

[xcpointx]

What kind of signal does this require:


and what kind of signal does this require


From what I can gather it has something to do with leading edge and trailing edge...? But how can I supply the required signals to switch?

Your help and advice would really be appreciated.

[niftydog]

555 timer in monostable mode.  These can create a pulse of fixed duration.  Make it a short duration as is practical and you'll get a quick pulse that has both leading edge and trailing edge.  Make one for each input and trigger with a switch.

[xcpointx]

sounds good! thanks for this!

1. SO i would build a circuit like this:
http://home.maine.rr.com/randylinscott/timer2.gif
?

Ive got a Midi Octopus switching unit which doesnt seem to do the required switching (only switches the inputs on the 2nd diagram ON but not OFF, and has no effect on the inputs on the top diagram.
If I measure the voltage on the Octopus's switching jacks, it goes from 0V (ground?) to 0.61V

2. Can I possibly use THIS signal as trigger for the 555 ? It is a latched signal though.

3. Would the output from the 555 go into the schematics input, or is it more suited to going in before those diodes?

4. Any idea why the resulting pulses on my schematics are inverted in comparision to each other?

Thanks so much!

[xcpointx]

Could this circuit maybe be expecting output from


1. a non inverting comparator
2. an inverting comparator?
[/b]

http://home.maine.rr.com/randylinscott/OPAMP2.GIF

Can anyone please comment?

[niftydog]

1. SO i would build a circuit like this:
http://home.maine.rr.com/randylinscott/timer2.gif

I would download this and use the information provided to build your own.  See page 7.

Just take note of how the trigger switch is wired in the gif you posted.

If I measure the voltage on the Octopus's switching jacks, it goes from 0V (ground?) to 0.61V

2. Can I possibly use THIS signal as trigger for the 555 ? It is a latched signal though.

The 555 requires a negative going pulse.  So it could be done, but if it latches off, you'll need to switch it on then off again before it triggers the 555.

3. Would the output from the 555 go into the schematics input, or is it more suited to going in before those diodes?

couldn't answer that without knowing the specifics of the signal that the circuit requires/outputs.  Best to try to trigger the existing circuit rather than putting it in before the diodes.  Suck it and see.  If it's doesn't work, put the 555 pulse through a logic inverter gate to clean it up and make it closer to 5 volts.  

4. Any idea why the resulting pulses on my schematics are inverted in comparision to each other?

because that's how it's designed.  The little circle on the output of those gates (U7) indicate inversion.  Probably something to do with leading/trailing edge triggered circuitry that follows.

Could this circuit maybe be expecting output from


1. a non inverting comparator
2. an inverting comparator?

it's possible, but given that it says (MIDI) on you original schematic I'd be tempted to say that it's expecting output from some logic gates.  Not knowing enough about MIDI, I can't really tell you.

A comparator would create a leading/trailing edge, and, designed with some hysteresis it's a good way of de-bouncing a switch...

but then again, many other logic devices do a similar thing... so do PICs and other micros.  Consider a PICAXE micro, easy to program and you can tweak the code around until you get what you want.  The right PICAXE can be programmed to control many, many inputs.  One chip solution to your problem!

It could be as easy as this;

Code Select Expand

PULSOUT 4,1
This command will pulse output 4 for 10uS.  You add more simple code to detect a switch on an input and then tell it to do the PULSOUT...


woah nelly... you could be digging a big hole for yourself here!

I've warned people on this forum in the past, that once you catch the bug, electronics can keep a hold of you for a long, long time.  I've been studying for four years and I learn something new every other hour of every day!  :shock: