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Step 11The Electronics
Now it's time to add some touch-sensitive wizardry! You could, of course, right up a simple toggle switch but that just isn't fancy enough.
The circuit itself is pretty basic. There are two halves, one for the white back light and one for the red subliminal message layer.
On the backlight layer, the capacitive sensor IC, upon detection of a touch sends a logic level "high" from its output pin. That signal goes to a D-type flip-flop which is configured (along with the assistance of an inverter) as an edge-triggered digital toggle switch. On each pulse from the sensor IC, the flip-flop's output toggles and latches in that state. That signal goes to a logic-level MOSFET which is used to control the current to the LEDs.
The subliminal message half is much simpler. The capacitive sensor is connected directly to the MOSFET, so that the LEDs only light when a touch is being sensed.
Also on the board is a small voltage limiter, that converts the 12V input to 5V for the capacitive sensor and flip-flop to operate.
Unfortunately the capacitive sensor is available only as a hobbyist-unfriendly WSON surface mount package. I knew I wouldn't have time to make a PCB, so I used a convenient little prototype board made by SchmartBoard. It has pads compatible with the WSON package, as well as numerous other package types. I simply chose components that would fit on the pad layouts available on the board.
The circuit itself is pretty basic. There are two halves, one for the white back light and one for the red subliminal message layer.
On the backlight layer, the capacitive sensor IC, upon detection of a touch sends a logic level "high" from its output pin. That signal goes to a D-type flip-flop which is configured (along with the assistance of an inverter) as an edge-triggered digital toggle switch. On each pulse from the sensor IC, the flip-flop's output toggles and latches in that state. That signal goes to a logic-level MOSFET which is used to control the current to the LEDs.
The subliminal message half is much simpler. The capacitive sensor is connected directly to the MOSFET, so that the LEDs only light when a touch is being sensed.
Also on the board is a small voltage limiter, that converts the 12V input to 5V for the capacitive sensor and flip-flop to operate.
Unfortunately the capacitive sensor is available only as a hobbyist-unfriendly WSON surface mount package. I knew I wouldn't have time to make a PCB, so I used a convenient little prototype board made by SchmartBoard. It has pads compatible with the WSON package, as well as numerous other package types. I simply chose components that would fit on the pad layouts available on the board.
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