555/4017 audio triggering

[bram]

Hi folks,

first post here. I'm planning to build a 555/4017 sequencer, of which I have found several interesting resources on the net. However, one thing I cannot find is how audio can trigger the 4017 decade counter.

I want to input a metronome/beat from my computer audiocard output into the sequencer, for it to run in sync with other beats/patterns coming out of the computer. I know that the astable 555 timer circuit acts as an LFO (range depending on the resistor/capacitor values), and that a monostable 555-circuit can deliver the short pulse which is needed for triggering the 4017 counter, like a manual step with a simple normally open momentary switch.

Can I use the tip signal of my audio output as the clock for the 4017 or do I need to build a monostable 555 circuit to deliver a short pulse? I thought of using a simple transistor (2N3904) as a swith with the tip signal going to C, B and E are the switch engaging the monostable 555-timer. Is this possible or am I forgetting something?

thanks in advance for the help.

[mikebike]

i would put somthing in between the audio signal and the 4017. the transister idea sounds good

but i think it can just recieve a trigger with out the 555. probibly need to ground the pulse from 555 when not in use

[expanoncolin]

i would put somthing in between the audio signal and the 4017. the transister idea sounds good

but i think it can just recieve a trigger with out the 555. probibly need to ground the pulse from 555 when not in use

This may work, but you probably won't get great results.  You want something like an "audio to gate" or "audio to trigger" circuit, which essentially finds the level of the audio signal and compares it to some threshold; when it's above, it outputs high, then low when the level gets below the threshold.  This is the same way a gate circuit works, except the gate signal in your circuit wouldn't be used to set the level of the output audio.

-Colin

[bram]

thanks for the help. I am indeed looking for an audio to gate circuit.

Actually this whole sequencer thingy should become something like a 'main clock' for my gear. I want to sync arpeggio and/or filter on a juno6, delay tempo on a Line DL4, tremolo/ring mod on a Moogerfooger 102. Furthermore I would implement a Sallen Key LP and HP filter (MS-20 clone by Tim Escobedo) and a Nyquist Aliaser (by JC Maillet). If all of this is synced by a beat running from my audio card, then I can combine loops/beats on the computer with analog effects on my play-along set-up.

For the DL4 tap tempo I'll use 2 4016 switches, with some additional wiring to a rotary switch to be able to sync the delay on tempo, tempo divided by 2, 4 and 8. I reckon switching the delay sync on the fly might generate some nice delay patterns.

Mikebike, I think if the incoming audio pulse is too long, it will trigger more than one step on the 4017, that's not what I want. Hence, a debounce circuit producing a short pulse to the 4017 which is triggered by an audio pulse (beat) which is longer than the outcoming pulse is what I'm after.

Do I need a decoupling cap on the audio in to the collector of the transistor?

[expanoncolin]

Do I need a decoupling cap on the audio in to the collector of the transistor?

I don't know what circuit you're referring to, but in general, yes - the transistor will not be biased around ground, so you will need a decoupling cap at the input to a transistor-based circuit.

-Colin

[bram]

I came across this:http://books.google.com/books?id=zGh0MRTYC9UC&pg=PA198&lpg=PA198&dq=fuzzy+dicer&source=bl&ots=KCLGeBNzfY&sig=vdZZkulsWdq7qJMmrKFoSoLos7U&hl=en&ei=bVHsS7H4A4G78gbHrti3BA&sa=X&oi=book_result&ct=result&resnum=6&ved=0CDoQ6AEwBQ#v=onepage&q=fuzzy%20dicer&f=false

on p 194 you'll find an envelope follower. Let the LED drive an optocoupler (4N25) which switches on a monostable 555 timer and I think this audio to trigger should work?