# How to transform this?

#### n0aim

Joined Nov 17, 2016
7
Hello!
Would anyone know how to transform this circuit into a boolean gate diagram and equation?

Thanks

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#### Papabravo

Joined Feb 24, 2006
12,702
Sure, it is a classic application of a sealing contact. In the initial condition the coil M is not energized, and the normally open contact M is open. With the pushbutton switches in their initial condition no current can flow through coil from one power rail to the other. Once the START button is pushed, the coil is energised, the normally open contact closes, and the start button can now be released since the contact M now provides a current path until the STOP button is depressed. Once the STOP button is depressed, the coil is de-energized and the contact returns to the open position.

Transforming the behavior into an equation and a gate diagram requires a bit more specification:
1. What gates are we allowed to use?
2. Can we use higher level functions like a latches or a flip-flops?
3. If answer to #2 is no, can we implement those functions with the basic gates described in #1?

Joined Jul 18, 2013
19,463
A fairly basic boolean circuit, there are different methods of expressing it, from simple boolean functions AND, OR, NAND, NOR etc, to more traditional arithmetic equations, or truth table.
Max.

#### n0aim

Joined Nov 17, 2016
7
Thanks for your answers guys! id like to know what the simplest way to express it is?

Preferably with AND OR NOR etc gates as it is all we have seen in class so far

#### WBahn

Joined Mar 31, 2012
24,978
Thanks for your answers guys! id like to know what the simplest way to express it is?

Preferably with AND OR NOR etc gates as it is all we have seen in class so far
It sounds like what you want is for someone to hand you a complete solution to YOUR homework problem.

Why don't YOU post YOUR best attempt at a solution and then let people help guide YOU to a solution?

#### n0aim

Joined Nov 17, 2016
7
It sounds like what you want is for someone to hand you a complete solution to YOUR homework problem.

Why don't YOU post YOUR best attempt at a solution and then let people help guide YOU to a solution?
This was in class work and the teacher himself was not sure. My best guess was to set up the NO contact with the start button in an OR gate. I realize this is not absolute because of the fact the relay needs to be energized before this is true.

#### Papabravo

Joined Feb 24, 2006
12,702
Well that is a start. What is the effect of the stop switch which is normally closed. What function does that suggest? You also need some way to remember that the contact associated with is closed when the coil is energized. What does "some way to remember" suggest?

#### n0aim

Joined Nov 17, 2016
7
The stop switch will break all current from continuing to the rest of the circuit. I had drawn it as a NOT initially then changed it to be A' in the OR gate with the relay's normally open contact.

As a class, this is our 2nd day in this course so my knowledge is very limited in boolean. Only the basic gates.

#### Papabravo

Joined Feb 24, 2006
12,702
The stop switch will break all current from continuing to the rest of the circuit. I had drawn it as a NOT initially then changed it to be A' in the OR gate with the relay's normally open contact.

As a class, this is our 2nd day in this course so my knowledge is very limited in boolean. Only the basic gates.
Not quite. The STOP switch is in series with the parallel combination of START and M. You already said that a parallel connection suggests an OR function. So a series connection suggests which of the logic function you have already learned about?

#### n0aim

Joined Nov 17, 2016
7
It suggests an AND

Stop AND start OR stop AND relay but thats not entirely true because M needs to be energized before the 2nd part be true

#### Papabravo

Joined Feb 24, 2006
12,702
You can factor the STOP from the terms that are OR'ed together to get

STOP & (START | M)

Where & stands for AND and the vertical bar stands for OR

Now all you need is a device that will remember the value of M when START is released and goes back to zero. This device is called a latch and it is a combinatorial circuit.

#### n0aim

Joined Nov 17, 2016
7
You can factor the STOP from the terms that are OR'ed together to get

STOP & (START | M)

Where & stands for AND and the vertical bar stands for OR

Now all you need is a device that will remember the value of M when START is released and goes back to zero. This device is called a latch and it is a combinatorial circuit.