Minimal toggle flip flop with discrete transistors required - diyAudio
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Old 21st August 2006, 10:30 AM   #1
heater is offline heater  Finland
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Default Minimal toggle flip flop with discrete transistors required

My young son has just been building a two transistor bistable (set/reset) flip-flop and the standard two transistor astable flip-flop (flasher) with a couple of LEDS in each. All as first steps into electronics.

His question now is how to make a bistable flip flop with only one switch as input that toggles on/off each time the switch is pressed. Obvious question but it has stumped me.

Years ago I did this by using two flip flops wired as a master and slave but this solution required many transistors and I'm not sure I could reproduce the thing anyway having hacked it on the fly at the time.

I have seen toggle flip flops built with two transistors, caps accross the base resistors and a parallel switch resistor connecting the emitters to ground (as here http://ourworld.compuserve.com/homep...wden/page9.htm) Fine but I would prefer the input to go into some more normal place rather than brute forcing the negative rail up and down. Also we loose 1 volt from the suply.

So the challenge is, does any one have any nice discrete transistor toggle circuits that:

a) Use minimal components as my sons patients for building things is a bit short at the moment.
b) Uses a more "logical" input method.
c) Runs from a 5 to 6 volt supply, dictated by our rechargeable battery pack.
b) Can be easily understood by a 12 year old beginner. (Or me for that matter)

Extra caps and diodes allowed.

Cheers all.
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Old 28th August 2006, 05:46 PM   #2
heater is offline heater  Finland
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I'm disappointed, no takers for this challenge, means I have to think about it myself

Attached is what I have come up with so far.

Any improvements, suggestions, comments?
Attached Images
File Type: png discrete_toggle_flipflop.png (13.1 KB, 267 views)
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Old 28th August 2006, 05:48 PM   #3
heater is offline heater  Finland
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Perhaps I should poit out that the input is the pulse supply on the left and outputs can be taken from any collector on the transistor pairs. Should have included LEDs there for a good demo effect.
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Old 29th August 2006, 12:56 AM   #4
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heater:
"I'm disappointed..."

that should not be please try the attachment
Regards
Heinz!
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File Type: txt toggle1a.asc.txt (2.8 KB, 97 views)
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Old 18th May 2010, 12:52 PM   #5
jwmbro is offline jwmbro  United States
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Hello DIYAudio,

funny this thread should exist, as I am currently looking to build nearly the same component.

I unfortunately have no idea what to do with a .asc.txt file, but I did look at heater's circuit:
Click the image to open in full size.

I have to say, wow, that's a lot of components.

Isn't there any easier (read, cheaper & smaller) way to build this circuit?

I don't really care if it uses transistors or relays, the important things are low cost, and hopefully also low power draw.

I found a circuit using three 4x relays, however those alone would cost about 21€, and seeing as I'm looking to build 5 flip-flops, 105€ is really too expensive for me.

Are there any cheaper ideas?
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Old 19th May 2010, 09:37 AM   #6
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If all you need is cheap, small and low power, just use two FF's in an IC -- 74hc74 or what was it again. Or even a 555.

Concerning discrete, how about this one:
Bistable Multivibrators or Flip-flops
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Old 7th February 2012, 07:02 AM   #7
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powerbecker did it. It has 2 npn trans, 6 resistor, 2 cap, and 2 diode.
i removed the .txt extension into .asc, and opened it with ltspice.
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Old 7th February 2012, 06:09 PM   #8
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by tengue17 View Post
powerbecker did it. It has 2 npn trans, 6 resistor, 2 cap, and 2 diode.
i removed the .txt extension into .asc, and opened it with ltspice.
The circuits shown will not actually work as the OP wants: they require debouncing and fast, clean edges.
Some more components would be required to make them work.

This circuit will actually work, and it is not more complicated.


As a bonus, one more based on a SCR:
Attached Images
File Type: gif Toggle2.gif (7.7 KB, 91 views)
File Type: gif ToggleThyr.gif (6.8 KB, 79 views)
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