Nuts and Volts - December 2015

32 December 2015

This article introduces programmable relays as a means of building a smart doorbell.

Programmable relays are microcontroller-based devices that can replace older hard-wired electromechanical control systems. A single programmable relay can replace an array of relays, timers, and counters.

THE SMART DOORBELL —

A Simple Programmable Relay Project FIGURE 1. Ladder logic tool bar.

Programmable relays use a visual anguage based on relay logic. Virtual devices are selected from a toolbar, configured from a drop down menu, and positioned on a ladder diagram between the power rails to achieve the required functionality (Figure 1).

The TECO SG2 Client Software Version 3. 37 illustrated in this article is downloadable for free from http://teco.us.com.

The visual ladder logic language was developed to ease the transition of people familiar with older electro-mechanical systems to newer microcontroller-based control systems.

The software allows for the simultaneous monitoring of multiple inputs, outputs, and virtual devices. Control functions can be complex, so the addition of comments into the ladder logic program can help to explain the workings of the system when in monitor mode (Figure 2).

Monitor mode allows an online computer to display the status changes of all inputs, outputs, and virtual devices as they occur.

The system designed in this article is a smart doorbell. It produces different ring patterns depending on when the door bell is pressed. The system utilizes a standard door bell and buzzer (Figure 3).

The intelligence is added to the system by the programmable relay. The programmable relay used in this article is a TECO SG2-12HT-D. It is available from FAC TORYMATION for $94. Additionally required is a SG2-Ulink cable for $33. Both are available at www.factorymation.com.