Gate Position Indication System

This project relays the main gate position (open or closed) to control panels located in two houses.

 

2nd house control box
The red pushbutton opens and closes the gate

 

Backside shot of sensor and magnet

 

Schematic Diagram

 

Relay driver circuit during functional test
L-R: Relay, SSR (red box), LED power supply

 

How it works:

The heart of the system is a burglar alarm component called a magnetic reed switch (the silver rod in the top photo. This one is used to sense roll-up door openings and is very robust and able to be used outdoors. The reed switch is very sensitive to magnetic fields and thus can sense a magnet over an inch away. With the magnet on the gate and the reed switch mounted to the gate post, the gate position can be sent to a remote location. So if the gate is commanded closed, the resident can positively know that the gate is closed by checking the position indicator LED. The reed switch can conduct only a very small amount of current when it is closed by the magnetic field from the magnet. So we had to employ a circuit that only used a few milliamps of current through the reed switch. A Solid State Relay (SSR) uses 1-2 mA and was readily available on the surplus market. The idea was to have the SSR actuate a larger dry contact relay where we could direct voltage to two LEDs that would indicate the position of the gate. The SSR has a triac in it and does not like to actuate inductive loads such as a relay coil. So we used a small incandescent light in parallel with the relay coil to make the SSR happy. The rest was easy. Using the single pole-double throw contacts on the relay, we send voltage to the remote LEDs that correspond to the position of the gate. A common dropping resistor of 1000 ohms was used to limit the current to the LEDs to about 12 mA at 12 volts.

 

Position control board before protective cover is installed

Surplus telco "66 Block" used for multiple systems interconnect

   
Projects

Gate 1

Gate 2

Tree Farm Home

1/03/17