My Nixie clock won’t have any visible buttons, so I chose to use a touch sensor, that signals to Arduino when the user touches the clock.
I brought from SureElectronics the Capacitive Proximity and Touch Button Control module, based on the IQS127D IC by Azoteq. You can download its datasheet and an important application note about how it detects a “touch” and how to design the sensing pads to optimize the detection process.
This IC can sense one touch pad and offers two digital outputs: proximity (red) and touch (yellow). SureElectronics included in the module two leds that show the output’s state:
The ouputs are normally (= no touch detected) at logic level high:
- if a finger comes near the sensing pad, POUT output is grounded;
- if a finger touches the pad, both POUT and TOUT are grounded.
It’s very easy to connect this sensor to Arduino: you need only two digital PINs to read (set them as INPUT) the status of the two outputs.
Using the ANT PIN you can connect to the sensor an external sensing “antenna”: it could be just a wire, a pad on a PCB…
The IC has an automatic antenna tuning algorithm (ATI) that detects external antenna’s peculiarities and automatically adapts to it.
I tested different materials (plastic, glass…) in front of my antenna (a wire) and the sensor was always able to detect my finger; here’s a short video about my tests: