Arbitrary digital signal with different pulse widths

Thread Starter

5O5mm

Joined May 15, 2021
4
Hi, I'm trying to generate a signal having different pulse widths but same OFF time. For example like this one:Adsız.png

I know such signal can be easily obtained by a microcontroller but my aim is to use discrete components.

First idea I came up with is using 555 timer and a multiplexer and counter. It seem to be working in theory but I couldn't obtain such a waveform. Also my intention is to have a long signal such this so I don't know what to use for that. Could you give any idea about obtaining such a waveform.
Thank you
waveforms-tim61.gif
 

crutschow

Joined Mar 14, 2008
27,225
Something like the LTspice simulation below of a pseudo-random generator, such as Ian0 suggested, with an added two flip-flop one-shot to give a low output that's never more than one clock-pulse period in width?
It requires 5 IC packages plus whatever may be needed for a clock generator.

1621228995680.png
 

Ian0

Joined Aug 7, 2020
2,235
It requires 5 IC packages plus whatever may be needed for a clock generator.
You can probably use a 4060, but it might not have the outputs that you need pinned out.
There's a table in Horowitz and Hill showing where the feedback points need to be for various different lengths. I'll scan it for you this evening.
 

Ian0

Joined Aug 7, 2020
2,235
My circuit is a shift-register whereas the 4060 is a counter, so it's not clear how that would work.
You’re absolutely right. I was thinking about multiple-stage shift registers and looked up multiple stage counters.
And the part I was thinking of is a 4006.
(Damn! I could have explained that away as a typo)
 

AnalogKid

Joined Aug 1, 2013
9,257
Since you want one phase of the output to be a constant pulse width while the other phase varies, two thoughts:

1. Rework the circuit in post #1. If the output of the 555 clocks the counter, you will get a four pulse repeating cycle. Bigger mux, longer cycle, but always a fixed pattern based on the resistor values. A variation of this eliminates the mux; the counter outputs drive the resistors.

2. Use any of a zillion PR circuits to generate a bit pattern where both phases vary in width (such as post #7), and have that signal fire a true monostable. The monostable will guarantee a fixed pulse width whenever triggered, and the time between triggers will be as random as you have money to throw at the PR source. Sunspots are nice.

BTW, the #7 circuit is a linear feedback shift register (LFSR), the cornerstone of many pseudo-random circuits and systems. National Semiconductor used to make an 8-pin IC that did this.

https://en.wikipedia.org/wiki/Linear-feedback_shift_register

I should have asked sooner - is this school work?

ak
 
Last edited:

andrewmm

Joined Feb 25, 2011
1,473
Is this not a PWM stream ?
or do you need a set of unique patterns to detect,

If its a number of patterns look at the Walsh transform,
For any given length of sequence ( power of two is easiest )
it provides a bunch of orthogonal sequences.
 

Thread Starter

5O5mm

Joined May 15, 2021
4
Since you want one phase of the output to be a constant pulse width while the other phase varies, two thoughts:

1. Rework the circuit in post #1. If the output of the 555 clocks the counter, you will get a four pulse repeating cycle. Bigger mux, longer cycle, but always a fixed pattern based on the resistor values. A variation of this eliminates the mux; the counter outputs drive the resistors.

2. Use any of a zillion PR circuits to generate a bit pattern where both phases vary in width (such as post #7), and have that signal fire a true monostable. The monostable will guarantee a fixed pulse width whenever triggered, and the time between triggers will be as random as you have money to throw at the PR source. Sunspots are nice.

BTW, the #7 circuit is a linear feedback shift register (LFSR), the cornerstone of many pseudo-random circuits and systems. National Semiconductor used to make an 8-pin IC that did this.

https://en.wikipedia.org/wiki/Linear-feedback_shift_register

I should have asked sooner - is this school work?

ak
Thank you all for the responds and interests. (sorry for the drawings I edited the screenshot in Paint) :
2.png

In fact I'm planning to use such a 'weird' signal to a generate a signal like above. The ON times of the square waves at a specific frequencies are determined by signal and the OFF times are constant. And the there may be, I don't know, 5 different pulse widths for timing and signal should be much longer.

Again I know it's super easy to generate it with a microcontroller, some code, pwm signal and constant delay but my aim is to use discrete components if it's doable.
Adsız3.png
 

BobaMosfet

Joined Jul 1, 2009
1,776
Hi, I'm trying to generate a signal having different pulse widths but same OFF time. For example like this one:View attachment 238583

I know such signal can be easily obtained by a microcontroller but my aim is to use discrete components.

First idea I came up with is using 555 timer and a multiplexer and counter. It seem to be working in theory but I couldn't obtain such a waveform. Also my intention is to have a long signal such this so I don't know what to use for that. Could you give any idea about obtaining such a waveform.
Thank you
View attachment 238584
You need to create a controllable counting circuit, first.
 
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