Self latching relays

[noobeestudent]

hi guys,

I am looking for self latching relays, can all relays be made into a self latching relay?

I am currently using a 5V 1A relay module. Once the relay is connected to a 5V Vcc suply and the input grounded, the normally open terminal will turn on, if the input pin is left floating or connected to Vcc then the relay will turn off.

But due to the limitation of the microcontroller i am using, i need to use a self latching relay.

is it possible to use this relay to design a self latching relay instead?

 

[treez]

A self latching relay is one where you close it by passing current through the coil, but then when you stop passing current through the coil, it stays closed. (or vice versa, ie open it).

If you want, you can add an electronic latch to the circuit, so that when the micro output stops passing current, the latch keeps passing current through the relay, so that the relay stays closed, (or stays open, whatever)............but obviously when circuit power is removed, the relay will un-latch....so this is not really a "latching relay"

 

[BradtheRad]

A microcontroller alone may not provide enough power to operate a relay. Attach a PNP transistor. Bias it so it turns on by default.

Apply 5V to the leftmost wire to turn it off.

 

[noobeestudent]

A microcontroller alone may not provide enough power to operate a relay. Attach a PNP transistor. Bias it so it turns on by default.

Apply 5V to the leftmost wire to turn it off.
View attachment 163153

i am actually using an air pump as a load, thus the relay to turn it on and off

 

[betwixt]

There is a transistor driver on that board already.
It 'might' be possible to adapt it to be latching but it would depend on the load and how it is wired. If the load is DC powered, you might be able to feed some of the switched DC back to the input pin through a high value resistor. The weak current through the resistor would keep the transistor conducting and in the 'latched on' condition. Sinking current to ground at the input would starve the base current and latch it off again. It would still unlatch if power completely failed and you would have to be aware that by linking input and output sides of the board you no longer have voltaic isolation.

 

[noobeestudent]

the load is actually powered by 240V ac mains, so i guess that what u are suggesting is not suitabe for it

There is a transistor driver on that board already.
It 'might' be possible to adapt it to be latching but it would depend on the load and how it is wired. If the load is DC powered, you might be able to feed some of the switched DC back to the input pin through a high value resistor. The weak current through the resistor would keep the transistor conducting and in the 'latched on' condition. Sinking current to ground at the input would starve the base current and latch it off again. It would still unlatch if power completely failed and you would have to be aware that by linking input and output sides of the board you no longer have voltaic isolation.

 

[d123]

Hi,

What is the limitation of the microcontroller, what do you mean?

There are latching relays.

To modify a normal relay, there are plenty of latch circuits you could add if you have PCB space anywhere. If you have more than one gpio, you could turn a variety of two-input logic latches on and off. That or on/off single-input latches.

Maybe one of these Latch and Toggle Power Circuits could be useful or give you ideas.

Google latch circuits and you'll find all manner of solutions.

--- Updated Jul 27, 2020 ---

This could be a good choice: cd4013 on off latch

 

[KlausST]

Hi,

Yes, what are the microcontroller limits?

It can't be pin count, because a latching relay needs more signals than a non latching.

What do you want? A mechanically (magnetically) latching or electrically latching (with extra circuit) solution?

Klaus

 

[noobeestudent]

what are the microcontroller limits?

Limitation of the circuit is because i dont have any extra interrupt ports to use to turn on the heater. Thus, i cant use the microcontroller to output 0 to turn it in and output 1 to turn it off.

electrically latching (with extra circuit) solution?

This would be better

 

[KlausST]

Hi,

You don't need interrupt pins to turn anything ON or OFF.

How do you activate/deactivate the latching relay? 0, 1, or 2 microcontroller pins?

Klaus

 

[noobeestudent]

Hi,

You don't need interrupt pins to turn anything ON or OFF.

How do you activate/deactivate the latching relay? 0, 1, or 2 microcontroller pins?

Klaus

Currently, i am doing it via programming, using a push button to interrupt. Once interrupt, the microcontroller will check on the state if the relay is on, it will be switched off and vice versa.

I would like to know if i can use a 2 push buttons, one to start and one to stop

 

[KlausST]

Hi,

I'm confused. Draw a sketch of your idea.

Now it seems you need/want the interrupt for pushbuttons (not for the relay). You may use interrupt, but there is no need for it.


Klaus