How to keep this latching circuit locking?

MisterBill2

Joined Jan 23, 2018
9,778
And now it is clear that what the TS wanted was an alternate-action circuit, not really a latching circuit. But not a hint of the power level, and that does matter. Push-on, Push-off is OK for some things, but I always prefer either an on-off switch or separate on and off buttons. Alternate action where one can't see the controlled thing can be rather unsafe. At one time the NEC stated " All switches shall have uniform on and off positions. That is why we no longer have those rotary light switches on the walls. Still on lamps, but not on walls. And I am not sure how 3-way switches fit with that rule.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
658
The circuit in post #1 does have positive feedback and so with some combination of resistance values it should latch to the "ON" state with a positive input from a source that has a high impedance when it is in the low state. So if the TS has a simulator it would just be a matter of experimenting to find the correct values for the resistors.
R4 must have a high value because iit only needs to compensate for the idle current when the base of Q1 is low. R2 must have a low enough resistance to keep Q2 saturated , or close to saturated, when Q1 is conducting because of the base current supplied by the input pulse and the current through R3. R3 must be a low enough resistance to allow enough base current for Q1 to stay conducting when the pulse is removed. R1 must have a low enough resistance to reduce the base current on Q1 when the input is held low.
With different resistance values the circuit will operate like a comparator, but not as fast or as stable.It would switch the relay load quite reliably as the input voltage would rise and fall. That may not be the form of latching that the TS is seeking, we have no comment about that.
Thank you.
I'll try the different R.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
658
And now it is clear that what the TS wanted was an alternate-action circuit, not really a latching circuit. But not a hint of the power level, and that does matter. Push-on, Push-off is OK for some things, but I always prefer either an on-off switch or separate on and off buttons. Alternate action where one can't see the controlled thing can be rather unsafe. At one time the NEC stated " All switches shall have uniform on and off positions. That is why we no longer have those rotary light switches on the walls. Still on lamps, but not on walls. And I am not sure how 3-way switches fit with that rule.
Thanks.
I do need a circuit, that can be trig by a HIGH pulse from a pin that always LOW except the pulse, and the circuit keep ON until next pulse trig it off and keep from the same pin or different pin.
 

MisterBill2

Joined Jan 23, 2018
9,778
It is also possible to create a set-reset latch (flipflop) using quad gates, possibly even a CD4001, the most common CMOS gate. probably it could be done with TTL also, but I have not designed with TTL and so I am not much help there.
The original circuit is probably unable to be adjusted for alternate action from a single button.With two buttons feeding the one input it can latch on or off, with either a "high" pulse or a "low" pulse, and a floating input the rest of the time.

But because we have no information about the application or the physical input device t is difficult to provide more help.
 

MisterBill2

Joined Jan 23, 2018
9,778
What we need is a description of the application, and an explanation of why two buttons are not available. And it appears that the TS is in a place where it is neither simple nor inexpensive to get electronic parts. It may not even be possible. I used to work at a place like that right here in the USA! The purchasing department would take three weeks for an emergency rush order.
 

eetech00

Joined Jun 8, 2013
2,644
Here is one way to do it with BJT's.
Works in simulation but I haven't tested it on the bench.
I tried to use parts from the TS parts list.

1634045400812.png

EDIT: Added Relay
 
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MisterBill2

Joined Jan 23, 2018
9,778
The circuit in post #30 will work, BUT it does not include a relay driver section , which is required and simple to add. This circuit can work with a button having the other side connected to the positive source.
The circuit in post #31 works BUT it requires an isolated button with neither side connected to anything. So if the button is not connected to any other point, then it can be used.
I have not seen any part list from the TS.

OK, now I see a part list in post #23, but that is only the parts in the circuit shown. I was thinking that the TS might have on hand. What sort of experimenter does not have any parts on hand???
 
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Thread Starter

LAOADAM

Joined Nov 21, 2018
658
Thank you.
I need it power off at next pulse, like many one button on/off circuit. seems this circuit can't get there.
like this one:
https://www.instructables.com/Three-Push-ON-Push-OFF-Latching-Circuits/
View attachment 248845is it possible changed into trigger-lock circuit?
Thanks
Hi,
I tested the circuit above that works well. the one button controlled the led ON and OFF.
I'd like to use the a 4n25 instead of the button, like the picture attached. p1's 4 and 5 hooked to p2's 4 and 5.
It can turn ON the led, can't turn it off, how to do?
Thanks
 

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MisterBill2

Joined Jan 23, 2018
9,778
Really, an alternate action push button is a poor choice because a noisy button contact will cause problems. And no way to assure that it will power up in the desired condition.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
658
Really, an alternate action push button is a poor choice because a noisy button contact will cause problems. And no way to assure that it will power up in the desired condition.
Thanks.
The purpose to use a 4N25, is for 5V signal to control the bistable multivibrator instead of a button.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
658
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