Hello HT,

Please educate me in distinguishing the difference between the following functions on a given switch:

1. On/Off Function - Okay, this one is pretty simple and I think I get it. So, when the user pushes the button it will turn on or off. Very simple.

2. Momentary - I understand this as this: in order for the switch to be turned on, the user needs to push the button and hold the button. Once the user lets off the button, it will turn off.

3. Latching - Please help me out with this one.

 

From wikipedia "A latching switch is a switch that maintains its state after being activated. A push to make push to break switch would therefore be a latching switch because each time you act on it, whatever state you leave it in it will maintain until acted on again."

Sound to me that it is the same as the on/off switch.....

 

any reply is appreciated.

 

you have kinda already answered you own question.

1. an ON/OFF switch is a switch that physically makes an electrical connection when you switch it. Unless you physically move it it can never change state.

2. A momentary switch makes an electrical connection while you are pressing the switch. It only changes state while you are acting on the switch.

3. Latching is a switch which memorizes state. If you were to use a momentary switch to activate a latching relay the relay would turn on and stay on with the first push of the button. Even after the button has been released. The second push of the button would turn the latching relay off. So its next state is dependent on its previous state.

I dont think you can say a push to make push to break switch is a latch. That type of switch requires a physical movement to change state. A latch only requires an electrical change 0->1 1->0 to change state. But if you wanted to argue semantics you could probably concieve that a mechanical latch is a latch.

 

Thanks for the explanation. I'm still having a hard time understanding the "Latching" switch. Is there an example that you explain with?

Thanks again

 

Ultimately, I need to know how a "Latching switch" acts.

For example, an On/Off switch just turns on when pushed and off when pushed again. Momentary switch stays on only when pressed and held.

How about a latching switch?

 

a latching switch turns on and stays on when you push the button. it turns off and stays off when you push it again. think of your defroster switch.

 

A latching switch is "in general" a switch that uses a momentary electrical switch to close and mechanically or electro mechanically, [relay] keep the switched circuit closed.

A good example, as mentioned, is using a momentary switch to energize a latching relay, or a pair of SPDT relays wired as a latching relay, often used as a passive "arming" kill switch in a car.

What is it you want to do that you need to know what a latching switch is??? 94

 

Keep in mind that a latch has memory. Which would also mean that if power was lost a latch could "reset" or forget its present state depending on design. When I say a state change do you know what I am refering to?

A latch will store its present state on its output until a state change on its input causes a change.

Think of a 2 input device, input a and input b with an output c.

A latch would be
A B C
0 0 current state=previous state
0 1 current state =1
1 0 current State =0
1 1 Illegal state

If you set your latch by setting A=0 volts and B=12 Volts C would equal 12 volts
Now if you set B=0 Volts C would still equal 12 volts because the previous value is "latched" onto the output.
The only thing that will cause C to go back to 0 is if you set A=12 volts and B=0 volts