Mercury switch is a Switch that looks like an LED bulb, but instead of a diode, it just has two poles and mercury inside the switch. Because mercury is liquid under ambient temperature, it will roll around inside and trigger the switch as the two poles have different heights(Fig. 1). This type of switch is most useful for tilt sensing devices. More information can be found here.

Fig. 1

Fig. 2 Shows the mercury switch in disconnected mode.

Fig. 3 Shows the mercury switch in connected mode.

Click here for information on where to buy it.

Hello World Example

The following example shows a mercury switch in action. Once the user tilts the switch, the Led1 on the mbed will go on.

#include "mbed.h"

DigitalOut led(LED1);
DigitalIn  mercury(p5);
int main() {
    
    while(1) {
        if(mercury == 1)
            led = 0;
        else
            led = 1;
    }
}

mercury_switch_hello_world_lpc1768.bin - has the compiled code. Save it on the mbed flash drive and hit reset.

Demo 2

This demo utilizes two mercury switches bent in the opposite directions. The code counts the number of tilting occurred in each direction to control the speed and direction of the motor. LED1 (fast) and LED2 (slow) on the mbed indicate that the motor is running in forward mode, and LED3 (slow) and LED4 (fast) indicate the motor is running in reverse mode. All LEDs are off when the motor is not running. It requires a H-bridge motor driver(TB6612FNG), a DC motor and an external power supply that can support the motor.

#include "mbed.h"
#include "Motor.h"

//DigitalOut led(LED1);
DigitalIn sw1(p5);
DigitalIn sw2(p6); 
BusOut led(LED1,LED2,LED3,LED4);
Motor m(p21, p11, p12); // pwm, fwd, rev

int main() {
    led = 0;
    m.speed(0);
    int count = 3;
    float speed = 0;
    while(1) {
    
        if(sw1 == 0 && count < 5)    
        {   
            count ++;
            speed +=0.5;
            m.speed(speed);
            if(count == 3)
                led =0;
            else if (count == 1)
                led = 0x1;
            else if (count == 2)
                led = 0x2;
            else if (count == 4)
                led = 0x4;
            else if (count == 5)
                led = 0x8;
            wait(1);
            
        }
        
        else if(sw2 == 0 && count>0  )
        {
            count --;
            speed -=0.5;
            m.speed(speed);
            if(count == 3)
                led =0;
            else if (count == 1)
                led = 0x1;
            else if (count == 2)
                led = 0x2;
            else if (count == 4)
                led = 0x4;
            else if (count == 5)
                led = 0x8;
            
            wait(1);
        }    
    }
}

mercuryswitchmotorcontrol_lpc1768.bin - has the compiled code. Save it on the mbed flash drive and hit reset.

Author : Hank Sun(Pangkai Sun), Soobum Kim