Introduction: Pressure Switch to Control 240 Volt Light

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I had been doing some photography work and wanted a better way to control the exposure lamp in the dark room so it could be turned on for a short time by stepping on a pressure mat switch.
A pressure mat switch can also be used to turn on a light from your front door or to practice Morse code. Or even scare intruders away :-).

The pressure switch controls the lamp via an electrical relay and is made from a couple of beer cans. These were connected with beer can wire, sandwiched between packing tape.

Supplies

2 Empty beer cans

Champagne cork

2 electrical terminals

5V to 240V Relay

Connecting wire

Packing tape

Insulation tape

Lamp

Step 1: Prepare the Plates

  • Cut open 2 empty beer cans and flatten into sheets
  • Sand both sides of the sheet with 180 sandpaper to make better electrical contact
  • Cut out a small tab from a corner of a sheet and shape to fit into an electrical terminal
  • Clamp on the electrical terminal

Step 2: Separate the Plates

  • Cut out some slices of cork from a champagne bottle top.
  • Glue 6 to one of a sheets so when the other sheet is placed on top there will be a small gap between the two.

Step 3: Apply Some Tape

  • Apply some tape around the edges. Secure the plates together with tape.
  • Test using a multimeter to check contact between the plates doesn't occur with no pressure.
  • Place under a mat and test with no pressure (off) and with pressure. I.e. foot pressure (On).

Attach wires to the terminals on the plates and connect to a relay or whatever else you want to switch on. For example: place the pressure switch under your front door mat and connect to a light via the relay to provide illumination when you arrive home at night.

The relay is a switch which uses a lower voltage (5 volts) provided via the pressure plate and a battery, to turn on a higher voltage switch (240 volts) within the relay box. It uses a Arduino Compatible 5V relay board which has been enclosed is a plastic box. The 240V positive is split and connected to the NO terminals (Normally Open). The 5V side is powered by a phone recharging battery pack via a modified USB cable which is switched on via the pressure plate switch. (To turn on, both the + and s pins need to be connected to positive). Only build the relay if you are competent working with a mains supply. I.E. know what you are doing.

Step 4: Wire the Pressure Plate to the Lamp

To switch on a 240 volt lamp using this pressure switch, run some low voltage wires to the relay. As I had no wires on hand I made some using beer cans. The wires were insulated from each other by being sandwiched between a couple of strips of plastic packing tape.
Stand on the pressure plate, the lamp will light up. Take your foot off and the lamp turns off. Just what is needed to control contact photographic exposure in the darkroom.

Step 5: Using It for Photography

Using the pressure plate switch in the darkroom worked well with good control over the contact print exposure lamp. This enabled a positive photo to be made from a negative one, taken using a pinhole camera.

Step 6: Take a Photo on Phone Using the Pressure Switch

After making the pressure switch to control a 240V light, I came across a recent instructable which takes a photo from a phone using a foot switch. So I applied the beer can pressure switch to the same task. It allows photos to be taken hands free and will come in handy for taking group photos or when documenting a project. If you want to use the switch by hand, half a tennis ball placed on the top makes for a good button.