Limit Switch Working
May automatic device weather consumer appliance or industrial devices, these types of switches use for safety or processing purpose.
In earlier my repair jobs about soap dispenser device, I found one confusing thing where on PCB pin no. 2 is grounded where Pin number 1 is Vin. Practically when we check the switch using multimeter on beep mode for continuity in ideal position (Switch is Not pressed) it showing continuity between pin no. 1 & 2; and when we press the switch this connection to pin no.2 becomes open circuit & we get continuity between pin no. 1 & 3. But as per the Connection on the PCB Pin no.1 is Volt in & pin no.2 is grounded so it creates shorting so how it actually works. To clear that doubt I Opened one similar switch to understand the working.
The internal contact connections look like this.
As seen in the image above, when the switch is not pressed, pins 1 and 2 are connected; however, as soon as the switch is pressed, pin 1 connects to pin 3, and pin 2 becomes open. In this configuration, pin 1 serves as the common voltage input, while pins 2 and 3 act as separate outputs as per requirement. but we can use this switch in many way as per our requirement.
Now come to the point; Regarding the doubt I raised in the previous article: Pin 1 was the voltage input and Pin 2 was the ground. So, when the power line comes into direct contact with the ground, a short circuit occurs; how does it work in that scenario?
When I traced the PCB I had obtained, the pins of that switch were utilized and connected in this manner. Pin no. 3 is used as Voltage input
Pin no. 1 is used as Output &
Pin no. 2 Is Ground.
The input at pin no.3 is left ‘floating’ (open) so that pin no.2 (ground) never comes into contact with input pin no.3.
In this way, the manufacturer had used this switch differently, depending on the device’s requirements.
This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.
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Note: You can check his previous repair articles on ACER Laptop Repaired For Intermittent Power Problem
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Ronny
August 8, 2026 at 10:48 am
You see corrosion like that in the microswitches on soda vending machines because of the moisture.