Is there a circuit for something like a 3-state monostable multivibrator? - Page 1
Forum section: electronics / projects

author: Timmy73
author_rank: Newbie
timestamp: August 19, 2020, 10:12:35 pm
content: 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

author: ledtester
author_rank: Super Contributor
timestamp: August 19, 2020, 10:58:55 pm
content: 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:

author: RJSV
author_rank: Super Contributor
timestamp: August 20, 2020, 11:47:18 pm
content: 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': thenThat 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.

author: RJSV
author_rank: Super Contributor
timestamp: August 21, 2020, 05:37:06 pm
content: 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 theCTR2 clock. Also used for your output.See pinout, CE must be 0 to count.R=1 to reset counter.

author: RJSV
author_rank: Super Contributor
timestamp: August 22, 2020, 04:55:38 pm
content: 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...

author: Timmy73
author_rank: Newbie
timestamp: August 24, 2020, 03:42:36 am
content: Ill just make something with 5 transistors

author: BrianHG
author_rank: Super Contributor
timestamp: August 24, 2020, 03:50:45 am
content: 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.