Fletchtronics

Laura is a photographer who has returned to school to learn all about cinematography. She asked me to build a brightness control gadget for studio lights. So for her birthday I built one.

Dimmer Box

WARNING:
This project uses high voltages. Be very careful at all steps and never touch any bare metal part of the device while plugged in. The wiring must be clean and very well insulated. Do not attempt to control any devices other than lamps. Fletchtronics cannot be responsible for any damage to yourself or your belongings, so take all possible precautions while working.

Dimmer Box Conceptual Diagram

There are lots of fancy dimmer switches available at your local home improvement and hardware stores. I opted for a model with two sliding dimmer controls. I feel that the sliding model offers more precision than the touch sensitive model, but your mileage may vary.

The same circuit here applies to a box with a single dimmer, only it has one less outlet, and for the project case there would be a dual gang box instead of triple.

Dimmer Box Schematic

The v+ net is connected to two dimmer switches in parallel, and is the line with varying resistance when the dimmer switch is activated. The v- net is the other side of the AC power supply and is connected directly to the outlets.

The gnd net is connected to the third prong of the supply outlet and to each device. This terminal or wire is most likely green, but check the documentation of the devices to be sure.

US Style Three Prong Outlet

On the US style outlet, v+ is connected to the larger of the two rectangular receptacles. v- is connected to the smaller rectangular receptacle. gnd is connected to the larger circular connection at the bottom of the diagram.

Dimmer Box Case - Triple Gang Box

For a safe electrically insulated case for the project, use a triple (or double, for a single dimmer switch) gang box made of insulated plastic such as this one. A nice feature of this model is that the power cable is nicely secured by a tough plastic spring-like piece at the bottom. A flat 6 foot appliance replacement electrical cord works very well.

Triple Gang Box Cover Panel

As a final touch and to complete the insulation, a decorative cover plate designed for a three gang box is screwed into the top, covering the gaps. With the cover plate in place, there is no exposed metal.

Tips

• Each side of an electrical outlet usually has two connected screw-in terminals. You can use this for example to make the v- net, connect v- from the power cable to outlet #1, then the connected terminal can continue with another piece of wire, connecting to the same net on outlet number 2. This saves wire and reduces the number of wire to wire connections.
• When you need to add your own wire, use 16 gauge primary wire. Anything thinner will cause heat.
• When connecting a braided copper wire to a screw terminal, make sure there is no extra copper strands protruding out. This could easily cause a short.
• When connecting wires together, use a screw on wire connector, which looks like a plastic cap with a metal threaded part inside. Twist the wires together tightly, then screw the wire connector over the connection and twist until tight.
• When testing, find a circuit in your house or apartment that is not loaded down with other devices. If you trip the fuse or circuit breaker, you don't want to end up erasing your unsaved thesis paper.

Future direction

A future project is to replace the dimmer switch with an AVR microcontroller, a small text LCD, and some buttons, along with a way to pre-program timed or random lighting effects. This project is currently in the prototyping phase, so keep your eye on fletchtronics.net for updates.