CV for vactrol rhythmic patterns?

gasboss775 · Joined: Jan 02, 2016 Posts: 217 Location: Scotland

This is probably the best solution.

Its a 4 bit R2R feeding a voltage to current converter to drive the led. This is the best way to drive LEDs when variable brightness is required as the circuit automatically overcomes the Vf of the LED using negative feedback.

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gasboss775 · Joined: Jan 02, 2016 Posts: 217 Location: Scotland

Using a binary counter and a 7 segment decoder to provide a complex modulation waveform

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PHOBoS · Posted: Wed Apr 26, 2017 5:12 pm Post subject:

what kind of decoder did you simulate to get 16 different steps ?
I looked at some datasheets but they all had blank outputs above 9 (10 steps). I do recall seeing one which did have
valid outputs above 9, but I can't remember which one it was.

I was thinking of making it into a synth module with potentiometers on the outputs (like a sequencer) but realized that
it is much easier to get the same results with a standard 10 (or more) step sequencer. I might experiment a bit more with
it as a suboscillator though, maybe add a switch for some different presets. I guess the easiest thing to use for that is some
muxes controlled by a single switch, that could possibly create 12 different ones with a standard rotary switch.

gasboss775 · Joined: Jan 02, 2016 Posts: 217 Location: Scotland

gasboss775 · Joined: Jan 02, 2016 Posts: 217 Location: Scotland

I have amended the circuit so that the counter resets at count=10 in other words a decade/BCD counter.

R2R and LED Driver(1).png

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PHOBoS · Posted: Thu Apr 27, 2017 4:03 am Post subject:

That's how I created the 10 steps too but it initially didn't work. The problem was that it would reset as soon as D becomes
high, so it only counted 8 steps. I had the same results with a CD4029 and a CD4040. To solve this I had to introduce a small
delay between output D and the AND gate which I did by chaining 4 gates in series. I used XNOR gates which is what I had
available in my modular lunetta but I guess using the remaing AND gates could have worked as well. Of course if you use
one of those chips with a built in counter it gets a bit easier.

I am actually wondering at the moment how hard it would be to create a reset at any given number of step >2 by uing the
a-g outputs. It is doable but might require a lot of gates. Looks like it could be a nice puzzle though.

gasboss775 · Joined: Jan 02, 2016 Posts: 217 Location: Scotland

PHOBoS · Posted: Fri Apr 28, 2017 7:38 am Post subject:

gasboss775 · Joined: Jan 02, 2016 Posts: 217 Location: Scotland

Another thing that I've tried is to put XOR gates ahead of the R2R one input is from a counter, etc and the other input is connected to a switch. The switch then decides whether the signal is buffered or inverted.

I was thinking of doing this with the 7 segment output going into an R2R. Not sure whether to have a 7 bit R2R or a 4 bit R2R with the option of picking which of the 7 outputs is routed to the R2R inputs via the XOR buffer/inverters.

gasboss775 · Joined: Jan 02, 2016 Posts: 217 Location: Scotland

Here is a schematic just to clarify what I was meaning in my last post:

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PHOBoS · Posted: Sun May 07, 2017 6:49 pm Post subject:

I just tested the reset circuit and it almost worked except the reset for 4 steps; it resets on 2 steps instead.
In theory it should work but I decided to add an AND gate to the I/O pin of the second mux too. (I actually
had this in the first design and then figured out that it shouldn't be necessary) This AND gate would be
connected to outputs f and g of the CD4026. As with the other mux I was going to use 2 diodes and a resistor
but after I added the diode to output g it already worked. Shocked

I am not sure why, but I have an LED display
connected to it so maybe the voltage drops a bit and therefor the reset doesn't properly work, I am using
4.7K series resistors for it though. It might also be caused by the mux itself.

Anyway, it seems to be working fine now so here is the updated version.

7-segment reset select V1_1.gif

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