SR Latch Within an SR Latch?

Thread Starter

sciengart

Joined Mar 25, 2020
26
Hey guys, I am at a loss for how to search google for what I am looking to learn about.
I was hoping someone would be so kind as to tell me what I am looking for...

I want to build a transistor only based Latch, a lot like the SR latch, but that has 3 or more states.
So when I press button A, LED A turns on and all other LED's turn off, Button B, LED B turns on and all other LEDs off, and So on into infinity... Or whatever.
I just need to know what this is called, I can do the leg work for finding schematics... I feel it should have a name...

Thanks for any help.
 

MrChips

Joined Oct 2, 2009
20,327
Hey guys, I am at a loss for how to search google for what I am looking to learn about.
I was hoping someone would be so kind as to tell me what I am looking for...

I want to build a transistor only based Latch, a lot like the SR latch, but that has 3 or more states.
So when I press button A, LED A turns on and all other LED's turn off, Button B, LED B turns on and all other LEDs off, and So on into infinity... Or whatever.
I just need to know what this is called, I can do the leg work for finding schematics... I feel it should have a name...

Thanks for any help.
It is called a "radio button" circuit.
 

MrChips

Joined Oct 2, 2009
20,327
Any reason why it must be transistors only?
You can simplify the design by using a priority encoder IC, SN74148, or CD4532.
 

dl324

Joined Mar 30, 2015
10,072
Welcome to AAC!

Here's a 4 button version using CMOS RS flip flops and OR gates:
1585242387124.png

EDIT: The OR gates can be replaced with diode OR gates. I designed a clocked R#S# flip flop for a discrete clock I was planning to build; so I can help with that if you get stuck.
 
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Thread Starter

sciengart

Joined Mar 25, 2020
26
Any reason why it must be transistors only?
You can simplify the design by using a priority encoder IC, SN74148, or CD4532.
because i am working on a design now, all electronic stores are closed due to the virus and my orders from ebay are all being held in montreal. and also because I prefer to work in transistors too!
 

MrChips

Joined Oct 2, 2009
20,327
In that case, you can build a flip-flop with two transistors and four resistors.
You will need one flip-flop for each output. One pushbutton each per flip-flop to SET.

Use diodes to RESET the other flip-flops. Let me know if you need a circuit.
 

Thread Starter

sciengart

Joined Mar 25, 2020
26
In that case, you can build a flip-flop with two transistors and four resistors.
You will need one flip-flop for each output. One pushbutton each per flip-flop to SET.

Use diodes to RESET the other flip-flops. Let me know if you need a circuit.
Thanks, I will try my best to realize it first and if after many hours I cant come up with a way, I will ask you! Thanks everyone for your help. Great community.
 

MisterBill2

Joined Jan 23, 2018
5,242
Hey guys, I am at a loss for how to search google for what I am looking to learn about.
I was hoping someone would be so kind as to tell me what I am looking for...

I want to build a transistor only based Latch, a lot like the SR latch, but that has 3 or more states.
So when I press button A, LED A turns on and all other LED's turn off, Button B, LED B turns on and all other LEDs off, and So on into infinity... Or whatever.
I just need to know what this is called, I can do the leg work for finding schematics... I feel it should have a name...

Thanks for any help.
The function described is a lot like a decoded counter. Possibly a CD4017 or equal. As each input pulse arrives the next output switches on and the previous one switches off. You could also consult a data book that gives the internal equivalent circuit of the IC and duplicate it with discrete transistors. But that would be really tedious.
But if you want to do it with discrete transistors then consider what is called a "ring counter." That can have any number of stages. And ring counters have been with us since before transistors.
 
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dl324

Joined Mar 30, 2015
10,072
I have 3904's, 2n2222's and 3906's.
I'd use the 2N3904's. It's It'd be a waste of 2N2222. If you had BC547, I'd use them instead because they're specified for a beta of 20 when used as switches; vs 10 for 2N3904.

EDIT: corrected typo.
 
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MisterBill2

Joined Jan 23, 2018
5,242
Now there is a bit of confusion as well as another question. It seemed from post #1 that the outputs would strictly come on in sequence, each time the button was pushed. Then I think came randomly selecting which one comes on.
And now my next question: What will the circuit do for you? Does it need to have useful outputs? Or deliver much power? At one time, 1964, flip-flops were built using power transistors and lighting 12 volt light bulbs. I will try to locate a ring counter circuit, which does exactly do what was originally asked for.
 

iimagine

Joined Dec 20, 2010
441
Transistors version of the circuit in post #8.
I dont think it could get much more simpler then this.

DeleteMe.PNG

EDIT: I forgot about saturation :rolleyes:
 
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crutschow

Joined Mar 14, 2008
24,403
Black & White version:
Question:
It looks like the 10nF capacitor will keep the reset signal to the transistors bases low after the set PB is released, which would mean everything is reset.
It would seem like you need a delay on the set to the PNP, not the reset (such as a cap from the PNP base to ground).

1585259357338.png
 
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