How to keep a signal to high state?

[engkeat]

I am using two push on button as a limit switch, when i press the push button, it will send a signal to the controller, but the signal will cut off when unpressed.. is there any method to keep the signal to high-state when the push button is unpressed?

 

[trekkytekky]

The state needs to be latched. If your controller is programmable the its simple.

Forgive the ASCII Ladder logic!!

 S1                     Q1
-| |-----------------( )-
                |
 Q1      S2     |
-| |-----|/|----|

Q1 goes high when S1 is pressed and turns off when S2 pressed

 

[oobuco]

Hi.

Maybe you will only need a pullup resistor.

Buco.

 

[trekkytekky]

A pullup resistor wont work as it will hold the output high constantly.

The switch inputs must be configured in a latch circuit so that it can 'remember' what it is currently doing. The code example is not just for a program solution, it can be translated to relay or electronic as well. It is simply a SET / RESET circuit that can be implemented as code OR with 2 transistors and 4 resistors in a DC electronic circuit OR a Set/Reset latching relay setup.

 

[isurug]

you might wnt to use a D flip flop if you wnt a professional and robust solution...

 

[trekkytekky]

An IC solution has voltage limits - typically 15V, a transistor solution will easily handle 50V or higher.

A D flip flop also requires a clock unless you use the Set / Reset overides if the device has one. Or you can just use a SR latch.

Both would require a Circuit board.

Neither would be my preferred solution, but I don't know what the 'controller' is, so I'm covering several scenarios.

 

[Gundam001]

Why used push switch, its better to have a slide switch if you want to maintain the logic high you need...



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[trekkytekky]

A limit switch usually is a momentary switch wired NO or NC depending on its use. The state needs to be latched if we need to detemine what it is doing.

Take a simple water tank example, with just a Low level limit and a High Level. Now if the low limit is not made we need to start to fill, as it fills the low limit gets made, but we need to keep filling until the high limit is made. Once full, we stop filling. As it empties, the High limit stops being made but we don't refill until the low limit is also not made. We need to latch the state to determine the action to complete.

This is a simple example because we are only performing the fill, so only one step requires remembering -Set on low limit being not made, Reset on High limit being made.