This capacitive touch sensor allows almost any small metal object to become a touch switch, controlling a variety of electrical devices via a 5A rated SPST relay or open collector output.


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SenSei is a quick and easy way to add durable interactivity to almost any conductive object. Developed by Box Fort for use in our museum exhibits and adventure experiences, the sensor is able to reliably detect human touch and provides convenient outputs to trigger other devices.


  • The sensor comes with a built-in relay that can turn a load on or off; up to 5 Amps of 120VAC wall current (or 5A 30VDC).
  • An alternative setting available on every board provides an open collector (sinking) output capable of sinking up to 350mA at 24VDC – perfect for integrating with Arduinos and other microcontrollers.
  • A removable terminal block and four large mounting holes make installation a snap.
  • The board requires 8-24VDC input power to operate. It consumes less than 100mA with the relay on, and less than 10mA with the relay off.
  • A built-in automatic reset recalibrates the sensor if it has been on for 60 seconds.
  • An on-board switch allows for 4 levels of easy sensitivity calibration.

Why Touch Sensing?

Wiring a few touch sensors into a project is an easy way to allow users to interact with the physical world in novel ways. We’ve used them around the shop to entertain ourselves; everything from music-playing doorknobs to booby-trapped office furniture.

We’ve also successfully used our touch sensors in a variety of museum exhibits and walk-through shows and now prefer the sensors to other forms of human input. Long after ordinary push buttons have been smashed to bits, a touch-sensitive metal plate barely shows wear. The exposed parts can easily be made as weather-proof, vandal-proof, or whatever-proof the application demands.

SenSei is able to detect right through most non-conductive materials (plastic, wood, glass, drywall, etc.) and the electrode can, therefore, be as obvious or inconspicuous as desired. While sensing touch directly off of a piece of metal is great for some applications, a small electrode inside a wall or hidden behind a graphic image can serve as a hidden button that detects proximity, or “near touch”, providing an unexpected interaction.

How it works

The sensor works by detecting a change in an electrical quality called capacitance. Whenever two conductive objects approach one another at different voltages, the charges on each object move around to try and get closer to the charges in the other. The result is a buildup of opposing electric charge on either side of the gap between the objects. This type of setup is called a capacitor.

When a person (or any large, semi-conductive object) touches the sensor’s electrode, it contributes a little bit of it’s charge to one side of a capacitor within the sensor. A tiny chip on board tracks this change and turns on the outp

Touch Sensor Manual

Additional information

Weight .1 lbs
Dimensions 2 × 2 × 0.5 in