Gadget Freak Case #238: Controller Adjusts Garage Lights Build Instructions

Transcription

1 Gadget Freak Case #238: Controller Adjusts Garage Lights Build Instructions The schematic diagram shows the main garage-light switch (SW1) that turns on both fluorescent lamps, Lamp 1 and Lamp 2. Only Lamp 1, placed above the retracted garage door, includes a solid-state relay in its circuit. When the garage door opens completely, a permanent magnet mounted on the door caused a small reed switch (SW2) to open. This switch controls current through the solid-state relay. So with Lamp 1 and Lamp 2 lit, when someone opens the garage door, Lamp 1 automatically turns off. This project has two primary assemblies; the junction box with the solid-state relay and transformer, and a door-position sensing switch. The junction box described earlier holds the solid-state relay, the low-voltage transformer, and the rectifier circuit (resistor R, and diode D). I chose a 4-inch octagonal metal box because you can easily add an extension--a "box" with an open back and front--that increases the depth of the box. The extension provides plenty of room for the relay. First I I removed one of the circular "knockouts" on the side of the box and secured the doorbell transformer in place. Figure 1. Low-voltage transformer attached to a 4-in. octagonal electrical junction box. In this image the box extended is already attached to the upper box. Second, I fastened the relay to the inside top surface of the box with machine screws so I could remove it if necessary. Then I used a small circuit board to hold the rectifier and connect directly to the solid-state-relay connection screws. The rectifier diode converts the AC current from the transformer to a DC current needed to control the relay.

2 Figure 2. This view inside the junction box shows the transformer (right), the solid-state relay, and the rectifier diode, resistor, and capacitor attached to the + and - control inputs on the solid-state relay. I have a box of salvaged relays already equipped with diodes, so I used one for this project. You can use a small piece of perf board or Veroboard to mount the diode, capacitor, resistor, and wires, as shown in the schematic diagram.

3 Figure 3. Circuit board with resistor, diode, and capacitor mounted and soldered in place. Two vertical spade lugs simplified connection to the transformer and reed switch. The holes aligned with those on the solid-state relay for the two control inputs. You can use a piece of perf board or Veroboard to mount your components. In all cases, ensure none of the electrical connections or leads make contact with the grounded metal box. Always ground a metal electrical box with the bare copper wire in the 12-2 or 14-2 cable that supplies power to the transformer and solid-state relay. Lamp connections require 14-gauge wire, NOT small-diameter hook-up wire. Remember, all electrical circuits in a garage must have a ground-fault interrupter. Check with your local town or county building department to ensure your installation of line power meets code requirements. Make all the necessary wiring connections and then attach the extension to the junction box. Secure the junction box assembly to the ceiling joist. You will run line power controlled by the solid-state relay from this box, so you will need to cut a hold in the ceiling drywall the size of the 4-inch junction box.

4 Figure 4. The 4-in. box and extension attached to a garage-ceiling joist. The white wires (14-2 Romex cable) provide connection to the 120V circuits. To sense the door position, I used a magnetic reed switch much like those used in alarm systems to detect an open window or door. This switch has a normally closed (N.C.) and a normally open (N.O.) contact. Use the common terminal and the N.C. terminal when you wire the reed switch into your circuit. This configuration keeps Lamp 1 on unless the open garage door blocks its light. Mount the switch on the garage-door track in a position so a permanent magnet on the door actuates the switch.

5 Figure 5. I used a piece of scrap metal to position the reed switch close to a place where I could mount a permanent magnet. I used a small junction box and EMT conduit (optional) to protect the wire between the reed switch and the solid-state-relay circuits. You might need to experiment with your mounting arrangement for the magnet and the reed switch to find the best places to mount them. I uses a piece of scrap metal to support the reed switch and attached the magnet to the edge of the door near the track. Electrical metallic tubing (EMT) protected the wiring.

6 Figure 6. A close-up view of the reed switch and permanent magnet. Editor's Note: You could use the normally open contact on SW2 to power an indicator light to let a driver know when the door has fully retracted. You don't want them to back into a partially opened door. If you don't have a magnet handy, one of the magnets used in a cabinet-door latch might work. And, it comes in a plastic holder with mounting tabs. You also could salvage a magnet from a PC speaker. Parts List Amt Part Description Allied Part # 1 Magnetic Reed Switch SPDT, 100V DC (SW2) Solid State Relay, DC60SA N5404 Diode, 3A, 400V (D) ohm, 1/4W, 5% Carbon-Film Resistor (R) uf Capacitor, Tantalum, 10%, 35V (C) Available from local Lowe s home-improvements Lowe s Part # store: 1 4-in. Octagonal Junction Box in. Octagonal Junction Box Extension in Square Cover Plate V AC Door Chime Transformer (T) 50500

7 1 Magnet Schematic Diagram

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