Is there a switch that only lights on whenever the load is on?

Thread Starter

bdalloul

Joined Oct 26, 2023
11
Hello, so I v been posting and asking questions about switches recently and I know how to connect them now; however, it seems that the LED in the switch is parallel to the circuit and there doesn't have to be a load for the LED to be on. I am using the MP004435 switch and connecting terminal 1 to the battery, term 2 to the load, and term 3 to the ground.
Now that is great, but the reason I chose to use an illuminated switch is for the LED to be an indicator that the load is on, so I expected the LED to be in series with the load. I don't have the schematics for the switch, its datasheet is really short, I am just assuming it is in parallel because it still lights on when there is no load. I expected there to be a pnp transistor that ensures the LED is on only when the load is on... I don't know what kinda switch is that.
I guess my first question is, am I connecting it correctly? And does it actually operate the way I think it does?
If yes, are u aware of any switches that act as indicators that the load is on?
Thank you!!
 

LesJones

Joined Jan 8, 2017
4,171
You need something in series with the load to sense current. The device sensing the current will always some voltage drop. You will have to decide what value of current turns on the indicator. The method used will depend on the voltage drop you can tolerate, the amount of current that is required to trigger the indicator, the maximum value of current that will flow in the circuit and whether the current is AC or DC.

Les.
 

Thread Starter

bdalloul

Joined Oct 26, 2023
11
You need something in series with the load to sense current. The device sensing the current will always some voltage drop. You will have to decide what value of current turns on the indicator. The method used will depend on the voltage drop you can tolerate, the amount of current that is required to trigger the indicator, the maximum value of current that will flow in the circuit and whether the current is AC or DC.

Les.
I am okay with a voltage drop on the illuminated LED and yes I made sure that the switch can handle both the voltage and current of my circuit. Are u aware of any switch with its LED in series? Like I need both capabilities (to switch on and off and an indicator that the load is on), I know I can use separate components like a switch and then an indicator LED in series, But there is an LED in the switch and it turning on without having a load doesn't make sense to me, I would expect to have the LED and load connected via a pnp so that the LED is only on when the load is on. If that makes sense.
 

LesJones

Joined Jan 8, 2017
4,171
Here is a link to an illuminated switch that would probably do what you want. There is a link to the datasheet on the switch in the link
Here is the way you would have to connect it.
LED switch001.jpgThe 4 diodes would need to be rated for the mximum current in your circuit.
I have assumed a red LED which would have a forward voltage drop of 1.8 volts.
The 4 diodes would give a voltage drop of between 2.4 and 2.8 volts.
The LED light for any current greater than about 10 mA in your circuit.

Les.
 

dl324

Joined Mar 30, 2015
16,654
I am using the MP004435 switch and connecting terminal 1 to the battery, term 2 to the load, and term 3 to the ground.
The datasheet is crap. It doesn't show how the LED is wired or give numbers for the terminals. Post a picture of the terminals with their numbers and show how the LED is wired.
 

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Thread Starter

bdalloul

Joined Oct 26, 2023
11
The datasheet is crap. It doesn't show how the LED is wired or give numbers for the terminals. Post a picture of the terminals with their numbers and show how the LED is wired.
This is how I connected it and it seems to work. However, I don't like how the switch light remains on even if I disconnect terminal 2 from the load
 

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Thread Starter

bdalloul

Joined Oct 26, 2023
11
That would be practically useless. The load could only draw the same current as the LED.
That is true..... hmm. well, I am doing this for an RF radio and its power consumption is 6W max and its voltage range is 6-42V. Now I have more questions lol. so its current draw changes as I change the voltage..? I dunno. it seems it doesn't need a lot of current anyway. I don't know how to know that information. I connected the radio in series with a resistor but the radio didn't turn on, it was a closed circuit though. I added a 1k ohms resistor and the voltage drop on it was around 8v out of 12v battery so the radio wasn't getting enough voltage to operate maybe? I still get confused when it comes to current and voltage and multiple loads....
 

LesJones

Joined Jan 8, 2017
4,171
Re post #5 As the datasheet does not give the connection you will have to identify them by testing. First identify the the switch contacts with resistance measurements. I think you have said that your switch has three connections so one side of the LED must be connected to the connection that was NOT one of the switch contacts. The other side of the LED must be connected to one of the switch connections but w don't know which one.
With the switch set to the open position, (IE infinite resistance between the contacts.) Get a supply of about 3 volts with one end of a 470 ohm resistor connected to the supply positive. Connect the supply negative to the connection that is NOT one of the switch contacts. connect the free end of the resistor to each of the switch connections in turn. If the LED lights then the that switch connection is connected to the LED anode and the LED anode is connected to the connection that is NOT eiter of the switch contacts. If the LED did not light remove the connection between the supply negative and the connection that is NOT one of the switch contacts. connect the free end of the resistor to this connection. Now connect the supply negative in turn to each of the switch contacts. If the LED lights you have identified the LED cathode. We are only ASSUMING that the light source is a LED. If it is a filament bulb you can identify the connection with resistance tests.
Les
 
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