Need a way to reset the timing on a Monostable 555 Circuit

Thread Starter

sciengart

Joined Mar 25, 2020
36
Why do you think that?
I don't know any better? :(
I tried the not gate,I don't know enough to figure out how, using my circuit to have that trigger pin go low.

Let me explain what I am doing.
I am trying to design an ADSR for a synth project I am working on. I find giving yourself a goal, motivates you to learn whatever you need to get it done, and you usually end up with a ton of knowledge. Each project, especially if very challenging, increases your skills.
I cant afford schooling, so I have to learn myself.
Books take me months to grasp, I am a hands on kind of guy, I guess its how my brain works.

So what I am reaching for right now, is just to develop this one step of the adsr.
If you know synthesizers, then you know that when you press a note ( on a synth with controllable adsr) the note:
-Stays pressed until you release it (no problem lol)
-decays in accordance to your decay timing <---- this is what I am working on now.
-re-triggers if you press again
-changes pitch if you press another note.

Now I can wire together two separate oscillators and have individual decays for each.
However, I need to be able to control them universally, and this is why I was working with the 555 timer. I need to simultaneously press the "note on" transistor switch, whilst also enabling the "decay on" switch and have the decay remain on, until the note voltage reaches zero.
Now in the perfect world I would do this using a comparator, however all I have is a 741, and the problem I encountered is as I reached the reference voltage the pitch would shift as the switch faded off.

I dont have any other ic's as mine are in customs, so Iam working with what I have. I cant go buy any because all the local stores are closed.

So I figured, if I could have a timing setting that correlated to the length of the decay using the 555 retrig, then when it goes high, both the pitch and decay switches go high, the pitch for that note stays at its pitch and the decay is allowed to run its cycle.

I know this is nearly a book, no one will read it... but on the off chance someone does and wants to suggest an adsr schematic...
I have just transistors, capacitors, resistors, a handful of diodes and 555 timers, 2 358's, 1 octo, and 2 741s.

And I prefer analog to digital audio synths. I draw the line at low level IC's.

I dont want to build the whole thing today. I just want to grasp a way to get the sound to decay and the pitch to remain steady.
 

Thread Starter

sciengart

Joined Mar 25, 2020
36
Yes, and that works, unfortunately, it also instantly discharges the cap, abolishing the timing aspect that I am so eagerly searching for.
 

eetech00

Joined Jun 8, 2013
1,990
Yes, and that works, unfortunately, it also instantly discharges the cap, abolishing the timing aspect that I am so eagerly searching for.
Hi

So, I think these are your requirements, please confirm.

1. Initially:
The timer output voltage is low.
Your control signal to the timer is high.
2. The timer will start timing when you send a "high to low" control voltage to trigger the timer.
3. When the timer is triggered, the timer output will immediately change from low to high for the timing duration.
4. If a high to low control signal is again sent during the timing period, the timing period will restart.
5. When the timing period ends, the output voltage returns to the "low" state.

Questions,
What is the power supply voltage?
What voltage levels will be used to trigger the timer?

eT
 

Alec_t

Joined Sep 17, 2013
11,640
Now I can wire together two separate oscillators and have individual decays for each.
However, I need to be able to control them universally
I don't see how universal control would be musically realistic. If you've already pressed and released note 1, then press note 2, surely you wouldn't want the decay of note 1 to be abruptly terminated and replaced by the decay of note 2?
Is your system going to be monophonic or polyphonic?
 

Thread Starter

sciengart

Joined Mar 25, 2020
36
I don't see how universal control would be musically realistic.
An envelope generator is not musically realistic? They are an invaluable tool, undeniably necessary to create unique sounds in analog synthesis. That's like saying having a beef patty on a beef burger is not realistic...
If you've already pressed and released note 1, then press note 2, surely you wouldn't want the decay of note 1 to be abruptly terminated and replaced by the decay of note 2?
Step 1: Make the first note continue decaying before introducing a second note.
As is, the current design with the not gate does the following:
1. Turns on when I press the switch (good).
2. Stays on if I hold the switch (good)
3. Retriggers if I let go and press again.
4. Discharges the cap as soon as I let go.

If I connect the trigger to ground via an spst, and throw the spst, it continues to allow the signal flow until the timing stops, then shuts off. (good)

However if I connect it to the not gate, it shuts off as soon as I release the button. This is because the connection to ground discharges the cap and waits for input to restart the timing again... Simply put, the 555 is nothing more than a bunch of wires that do exactly what a normal spst does in this configuration.
 
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