tap tempo circuit

elektrouwe · Joined: May 27, 2012 Posts: 146 Location: Germany

in times of 50cent 8 pin microcontrollers this circuit comes really 40 years too late. But hey, if you try to repair a defective ATTINY tapper in 10 years, you will be in deep sh*t with your present win10 toolchain Wink

This circuit works well in simulation. I designed it just for fun, but would like to hear about if someone will build it.
how it works:
the circuit has a digital ramp generator - CD4040 with R2R DAC clocked by start/stop oscillator U4,5 - and an analog ramp generator around C2.
Both oscillators are controlled by state flip flop U1,3. 2 momentary push switches TAP1,2 are used to tap in tempo.
1st state starts with hitting TAP1 :
DAC voltage restarts @ 0V and, by count-on/off control from comparator U6, then tracks the analog ramp.
BTW: ramp voltage does not rise linear (RC charge), so because DAC voltage tracks ramp, it is also nonlinear. This has no effect on tap tempo !
2nd state begins by hitting TAP2 :
4040 clock is stopped and DAC voltage freezes. This, now constant, voltage will be used as upper threshold for the analog ramp generator :
C2 is reset, whenever ramp voltage reaches the stored DAC voltage. Thus all consecutive ramps will have the exact shape (within 1 DAC step)
and timing as the first ramp between TAP1 and TAP2 time.

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Grumble · Posted: Fri Dec 13, 2019 11:53 am Post subject:

I can’t help wondering what a 4040 will cost you in 10 years Rolling Eyes

PHOBoS · Posted: Fri Dec 13, 2019 2:43 pm Post subject:

I haven't really studied the circuit yet but that R2R is unfeasible in practise. Resistors simply won't be accurate enough
(or they get very expensive). You might get to 6 bits or even 8 but I doubt you'll be able to get much more than that.
You could use a precision DAC if you can find a suitable one.

elektrouwe · Joined: May 27, 2012 Posts: 146 Location: Germany

PHOBoS · Posted: Sat Dec 14, 2019 3:47 pm Post subject:

Grumble · Posted: Sun Dec 15, 2019 4:02 am Post subject:

To say something in favor of the arduino knockoff boards: I made a tap-tempi module myself, that can simultaneously output a 1x, 2x, 3x and 4x HIGHER tempo as the one tapped or clocked as well as a switchable output to choose one ofthe tempi bounce

Try that with some 4000 cmos chips Wink

elektrouwe · Joined: May 27, 2012 Posts: 146 Location: Germany

PHOBoS · Posted: Sun Dec 15, 2019 3:09 pm Post subject:

ok, yeah then I get how it works Smile

I don't think I've seen a capacitor being used to add hysteresis before.
Counters and magnitude comparators was indeed the direction I was thinking.

For the resistors I wonder if it is worth while to use arrays of 1 value and either use 150K with 2 in parallel for 75K (probably easiest)
or 75K and 2 in series for 150K. I guess with this amount of resistors you might as well get the values seperate.

elektrouwe · Joined: May 27, 2012 Posts: 146 Location: Germany

dk · Joined: Feb 12, 2019 Posts: 115 Location: Europe

Cool idea! Just a thought from the user interface side of things, but would it not be more comfortable to throw a flip flop in so you could use just one button instead of 2?