Making a set and reset circuit

Thread Starter

chuayq

Joined Jan 16, 2017
7
I know this should be pretty easy but I can't seems to wrap my head around creating this circuit.

The scenario is when the switch(S1) is closed, the lamp will turn on, when S1 is open, the lamp will turn off. There is an additional push button switch turning off the lamp but the lamp should not be back on until S1 is closed again.

The only restriction is that I can only use switches and relay, as I don't not have access to other hardware. I tried a few ways to connect a set and reset latch circuit but it doesn't fix the entire scenario that I wanted

Chua
 

WBahn

Joined Mar 31, 2012
29,979
What kind of switches and relays do you have access to?

It sounds like you made some attempts, so as already suggested post what your best attempt to date is and describe the manner in which it isn't meeting your required specs.
 

Thread Starter

chuayq

Joined Jan 16, 2017
7

WBahn

Joined Mar 31, 2012
29,979
I know this should be pretty easy but I can't seems to wrap my head around creating this circuit.

The scenario is when the switch(S1) is closed, the lamp will turn on, when S1 is open, the lamp will turn off. There is an additional push button switch turning off the lamp but the lamp should not be back on until S1 is closed again.

The only restriction is that I can only use switches and relay, as I don't not have access to other hardware. I tried a few ways to connect a set and reset latch circuit but it doesn't fix the entire scenario that I wanted

Chua
Part of the problem is that you have a self-contradictory set of requirements.

You say that when s1 is closed that the lamp is on. But then you later describe a situation in which it appears that S1 can be closed yet the lamp should not be on.

If I am reading between the lines correctly (i.e., guessing -- and engineering is not about guessing), the it appears you want the following behavior:

Starting with S1 open and the push button up, the lamp should be off. If the button is pushed at this time, nothing should happen.

If S1 is closed, then the lamp should light. If S1 is then opened, the system should return to the state it was in above. If, however, the push button is pushed then the lamp should turn off and remain off until such time as S1 is opened and then closed again.

If that is correct, look at it carefully and see what piece of information the relay needs to store.
 

Thread Starter

chuayq

Joined Jan 16, 2017
7
What kind of switches and relays do you have access to?

I have access to push button and toggle switches. I most probably can buy new hardware if needed. The relay I have I believe is Single Pole Double Throw SPDT

It sounds like you made some attempts, so as already suggested post what your best attempt to date is and describe the manner in which it isn't meeting your required specs.
Try 1: http://tinyurl.com/z3esmq8
The E-Stop needs to be a push button. The rest of the specs did meet my requirement, it's a simple circuit too. The only problem is I need the E-stop to be a push button.

Try 2: http://tinyurl.com/hnrdpew
Added a relay but it's the same as Try 1. The relay is totally redundant.

Try 3: http://tinyurl.com/jervuff
The E-Stop did meet the requirement now. But now S1 didn't meet the requirement, I need the S1 to cut off the lamp when the switch is open.
 

Thread Starter

chuayq

Joined Jan 16, 2017
7
Part of the problem is that you have a self-contradictory set of requirements.

You say that when s1 is closed that the lamp is on. But then you later describe a situation in which it appears that S1 can be closed yet the lamp should not be on.

If I am reading between the lines correctly (i.e., guessing -- and engineering is not about guessing), the it appears you want the following behavior:

Starting with S1 open and the push button up, the lamp should be off. If the button is pushed at this time, nothing should happen.

If S1 is closed, then the lamp should light. If S1 is then opened, the system should return to the state it was in above. If, however, the push button is pushed then the lamp should turn off and remain off until such time as S1 is opened and then closed again.

If that is correct, look at it carefully and see what piece of information the relay needs to store.
Thanks for your prompt reply! Yes, that's what I want. You have read in between the lines correctly. :)

Regards,
Chua
 

WBahn

Joined Mar 31, 2012
29,979
Thanks for your prompt reply! Yes, that's what I want. You have read in between the lines correctly. :)

Regards,
Chua
Okay, so next you need to identify your states. You have two inputs, S1 and S2, both of which can either be open or closed at any moment in time. Your states tell you everything you need to know about past events leading up the present moment when you look at the inputs and must decide what to do. For instance, in this case if you look at the switches and see that S1 is closed and that S2 is open, that is not enough to tell you whether the light should be on or off, is it? So need to identify what past information you need to store that will allow to make that decision based not just on the present condition of the inputs, but also which state you are presently in.
 

Thread Starter

chuayq

Joined Jan 16, 2017
7
Okay, so next you need to identify your states. You have two inputs, S1 and S2, both of which can either be open or closed at any moment in time. Your states tell you everything you need to know about past events leading up the present moment when you look at the inputs and must decide what to do. For instance, in this case if you look at the switches and see that S1 is closed and that S2 is open, that is not enough to tell you whether the light should be on or off, is it? So need to identify what past information you need to store that will allow to make that decision based not just on the present condition of the inputs, but also which state you are presently in.
I have identify the states on the present condition on the table below.
S1 S2 Lamp
0 0 0
0 1 0
1 0 0
1 1 1

Using the table about it's a AND condition which is how I came out with Try 1. However, I am caught blind sided by the push button condition.

I have no idea how to identify the past information and store that in a circuit. How can I do that?

Regards,
Chua
 

WBahn

Joined Mar 31, 2012
29,979
I have identify the states on the present condition on the table below.
S1 S2 Lamp
0 0 0
0 1 0
1 0 0
1 1 1

Using the table about it's a AND condition which is how I came out with Try 1. However, I am caught blind sided by the push button condition.

I have no idea how to identify the past information and store that in a circuit. How can I do that?

Regards,
Chua
The "state" does not map to the input conditions, it maps to a particular history of the circuit. But aside from that, look at your table closely. You are saying that the lamp is only on when both S1 and S2 are closed (assuming that a '0' is open and a '1' is closed). Is that true?

Furthermore, I thought we had already established that just knowing the present condition of the switches was not sufficient for you to know whether the lamp should be on or not. If S1 is closed, the lamp should be on if only if S2 has no previously been closed since S1 was last closed.
 

WBahn

Joined Mar 31, 2012
29,979
After you've given the prior questions some thought, the next thing is to tackle, in general, your question of how you can store information about past events using a relay.

The answer is that you want to configure it as a latch in which one even energizes the relay in such a way that it stays energized even after the triggering event is over until some other even causes it to de-energize.
 

Thread Starter

chuayq

Joined Jan 16, 2017
7
The "state" does not map to the input conditions, it maps to a particular history of the circuit. But aside from that, look at your table closely. You are saying that the lamp is only on when both S1 and S2 are closed (assuming that a '0' is open and a '1' is closed). Is that true?

Furthermore, I thought we had already established that just knowing the present condition of the switches was not sufficient for you to know whether the lamp should be on or not. If S1 is closed, the lamp should be on if only if S2 has no previously been closed since S1 was last closed.
Yes, that is true only in the first present state. When S2 is pushed(open and close) it should cut of the lamp until the next "open and close" of S1, which requires to look at the history of the state as when S2 is pushed, it actually goes through 2 states.

Yes, I know what you mean is that there is a need to configure the relay is such a way to fit my requirement but I have been thinking for about a week now and can't seems to find a way to do that. If you have the solution, can you provide some hint?

Regards,
Chua
 
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