Author Topic: Is there a circuit for something like a 3-state monostable multivibrator?  (Read 1008 times)

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Offline Timmy73Topic starter

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Is there? Im making a video generator (creates a movable and size-adjustable cursor on a composite TV set) and Im wondering if there is a circuit like a monostable multivibrator where its "off" for some time, then "on" for a while, then remaining "off" until the next trigger pulse?

I imagine there is something like a Ring oscillator that would do this. I would prefer that this circuit can be made with 3 discrete transistors.
Thanks,
Tim
 

Online ledtester

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Sounds like you want a "pulse delay" circuit.

You can make one with a CD4098 -- a dual monostable multivibrator. Here's the basic idea from the datasheet:

1050222-0
 
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Offline RJSV

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Perhaps way overbuilt, take a glance at my 2 IC plan, uh 3 IC plan.  Photo diagram shows a pair of CD4017 counters.
Rotary switch, select your 'off time': then
That pulse coming, second CTR runs, timing out the 'ON timer'.
The 'TRIG in' acts as described, starting (both) CD 4013 back to '00'.
  Rotary six POS, plus SPDT, will switch one of 12.
 

Offline RJSV

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Here is better schematic, has two CD4017, and a 4013 (f/f pair).
Starts out '00', both f/f off, CTRs clear.
Then '01', TRIG in sets f/f 1, that allows CTR1 clock.
With '10', (read the bits rt to left). with count=7 the pulse clears f/f one, sets f/f 2. This allows the
CTR2 clock. Also used for your output.
See pinout, CE must be 0 to count.
 R=1 to reset counter.
 

Offline RJSV

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To avoid the 'TRIG' input from affecting the sequence, I made changes. This schematic features less IC count, by taking both types of counts, in one CD4017 IC.
First, notice the 'state 0' output is unused, as you need to time at least one (clock) count. Next, see the first f/f stays set, usual dual multi-vibrator circuit will also have some way of avoiding a re-trigger, until cycles complete.
Meanwhile, arrival at a first-count sets the output f/f, and a second-count times that (output pulse).
For example, you can set 3 clocks as first timer, that's 500 nSec. (6 MHz clock rate, from video sys).
Then, a second rotary switch, sets T2=3 clocks, also, for a 500 nSec output pulse (followed by all clear state.)
Of course, a 'bug' there, as the rotary settings should be overlapped. Plus, not ideal as rotary mis-settings are possible. Some 'glitches' might literally only  cause a slight flicker, as this is for a screen curser timing...
 

Offline Timmy73Topic starter

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Ill just make something with 5 transistors
 

Online BrianHG

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There is a lot here:
https://www.eevblog.com/forum/projects/oscilloscope-pong-for-1-or-2-players/

A number of pages in, a composite video PAL version was engineered as well.
Around page 14.
All transistor, no opamps or any ICs.
« Last Edit: August 24, 2020, 03:59:20 am by BrianHG »
 


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