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This section introduces a prototype of a touch sensor board, which can work as an input device for a microcomputer.
This touch sensor board has 4 sensors, which do not relying on any mechanical parts. These sensors can respond only gentle touching. Also, these sensors can work correctly even though the sensors are covered by a type of insulator such as plastic. If these sensors are pasted inside of a completely closed box, the sensors work appropriately. As the sensors can be put inside of a waterproof case, they still works well.
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These sensors start working as they simply connect to LSI controller. These sensors, which are attached on a circuit board, are connected to 4 sensor terminals of the LSI. Each sensor is made form a large round-shaped pattern, and its size is 10mm-diameter. Each sensor outputs the present status to its corresponding output terminal. As these output terminals are connected to a microcomputer, the sensors can be used as switches.
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Basically, the output terminals are open drain, and they require pull-up resistors if the terminals are attached to a microcomputer. For this touch sensor board, since pull-up resistors are already equipped with the touch sensor board, the pull-up resistors are NOT required.
VCC terminal is attached to the power supply. The voltage range of power supply is from 1.75V to 5V, and the supply should be very steady. The voltage level of VCC terminal is usually adjusted to microcomputer's one. Its output signals are at the lines from GPO0 to GPO3, and these lines are connected to the input terminals of the microcomputer. Because the touch sensor board comes with pull-up resistors, he additional pull-up resisters are not required.
To confirm the operation of this touch sensor board, a simple test board is created. The touch sensor board is examined with the test board. The test board is equipped with a power supply input, a connector for the touch sensor board connector, and LEDs. The LEDs are used for displaying the present status and visually confirming the operation of the board.
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The schematic of this test board is on Overo-002-0002A_sch.pdf. The outputs of the touch sensor board are connected to the LEDs. To touch each sensor on the board, its corresponding LED turns on.
- Touch sensor board schematic
- Test board schematic
- 2012/3/06 The article is initially uploaded.
OVERO-002-0001A_sch.pdf