Is a Tri-Stable Multi-vibrator even possible?

Thread Starter

ConstantineOfTexas

Joined Jun 27, 2017
44
Using Tutorial 8, the Dual Flasher Circuit, from the Starting Electronics website I designed a Tri-Stable Multi-Vibrator, so-called because I investigated this circuit and similar ones that described it as a Flipflop Circuit and as a Bi-Stable Multi-Vibrator. This is what I came up with:

TristableMultivibrator.jpg


Unfortunately, I can't seem to get it to work. Any suggestions or did someone actually get it to work?
 

Alec_t

Joined Sep 17, 2013
10,376
Any suggestions or did someone actually get it to work?
It works fine in simulation. Try adjusting one or other collector resistor value to unbalance the circuit slightly. That may help to get oscillations started.
Depending on the LEDs, you may need to reduce R6 to get the blue LED as bright as the others.
Is your circuit on a breadboard? If so, double-check all connections.
 
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Thread Starter

ConstantineOfTexas

Joined Jun 27, 2017
44
It works fine in simulation. Try adjusting one or other collector resistor value to unbalance the circuit slightly. That may help to get oscillations started.
Depending on the LEDs, you may need to reduce R6 to get the blue LED as bright as the others.
Is your circuit on a breadboard? If so, double-check all connections.
So far, all the lights flash at once and then it stops.
I think this is the winning idea and I am going to go with it.
 

DickCappels

Joined Aug 21, 2008
5,895
It is just a ring oscillator. Oscillates very reliably, even without the capacitors. Just use an odd number of stages. The base resistors are not really needed for oscillation.
upload_2019-2-11_2-1-28.png
 

Thread Starter

ConstantineOfTexas

Joined Jun 27, 2017
44
I have been busy these last couple of days. I did find some problems:
1) I had a defective breadboard
2) I used the 2N2222A transistor, not the 1N2222
Despite correcting these problems my project still failed, so I did some simplifications:
1) I went back to the old Starting Electronics Boilerplate, substituting the parts specified to build the Bi-Stable Multi-vibrator.
2) I used Alec_t's suggestion to vary the resistances slightly on the leds.
3) I simplified further to a single transistor and led, doing away with the capacitors to get the simplest circuit that didn't work:

Subcircuit.jpg
The problems go away when the transistor goes away. What am I doing wrong?
 

MisterBill2

Joined Jan 23, 2018
3,884
I did create a "TRi-Flop circuit for one application and it serves very well. It has three states, 0,1, and 2.t will always return to the "0" state if left alone. It consists of a two stage counter using a CD4013 dual D FF, but with each "Q" output feeding back to the resets with a high value resistor, and a 0.1 mfd capacitor from the reset to common to slow the resetting.
Actually, it is the logical extension of the "Flop-Shot" circuit, invented by others.

The circuit posted first in this thread is a ring counter, quite useful but not new.
 

DickCappels

Joined Aug 21, 2008
5,895
Without the transistor the current through the LED has no path to the negative battery terminal but the LED lights?

If it does light with the transistor removed that would mean that your circuit is not connected correctly.
 

Thread Starter

ConstantineOfTexas

Joined Jun 27, 2017
44
Thank you, Mr Bill, for the identification of this circuit as a ring counter. The internet resources use flipflops, integrated circuits for which I am not yet ready to try. I really need to be conversant with transistors first. Still, if you have any reference material, I am interested.

As per my problem with the transistor, I have refitted it several times, even reversing it, and still nothing. It might be defective, so I'm going to have to test it. I plan to even test the circuit while its running with a voltmeter.

Nevertheless, I think I need some Theory here. What does it take to properly turn on this 2N2222A transistor? How many Amps or Volts or Watts? For example, I calculate 16 millivolts and 17 milliamps going to the base of Q1. Are my numbers correct and should that turn on that transistor, or do I have defective parts?
 

MisterBill2

Joined Jan 23, 2018
3,884
Changing R2 from 15K ohms to 1000 ohms should result in the base to emitter voltage rising to about 0.7 volts, and the LED illuminating a bit. That will give an indication that the transistor is both functional and connected correctly, and that it is an NPN device.

The fact is that many digital CMOS IC devices are a lot simpler to use than transistors. Often the real challenge is keeping track of pin numbers. Other kinds of digital devices are sometimes more demanding to work with. The Tri-Flop circuit is about as simple as things get for multi-state logic functions. AND the CD4013 is commonly available cheap, except for a few quite expensive sources.
 

Thread Starter

ConstantineOfTexas

Joined Jun 27, 2017
44
I took MisterBill's advice. It was good advice, but nothing happened. Nor could anything happen in retrospect.. The voltmeter confirmed that the Transistor was a dud.
 

eetech00

Joined Jun 8, 2013
1,661
The circuit in post #1 will work if you add a startup circuit to make begin oscillating.

Add a larger cap, maybe 100uf, from +5 thru a 1k resistor to ground. Then connect the junction of the cap and resistor to the base of Q1.
It should begin to oscillate at a rate easy to see.

eT
 
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