For push-button phones, when the asterisk * is pressed, the IC1 DTMF decoder control logic remains. The audio off-hook of the IC4 FM audio receiver is placed on the telephone line RY2 which is a DPDT 12V relay. To keep the caller ID, press the touch-tone phone star key and hang up.
What is a membrane switch?
A membrane switch is an operating system integrating key function, indicating element and instrument panel. The membrane switch, also called a membrane keyboard or membrane keypad, is a custom switch assembly that uses pressure to open or close the conducting path in an electrical circuit. The ultimate purpose of a membrane switch is to serve as the interface between man and machine, enabling an operator to communicate with a piece of equipment, instrument, or machinery. Membrane switches are still consistently utilized as user interfaces for a wide range of products from industrial machinery to medical devices to agricultural equipment. Even the most rigorous of industries can count on proven membrane switch technology to provide a reliable, long-lasting human-machine interface.
How about the construction of a membrane switch?
A membrane switch assembly differs from traditional mechanical switches. Membrane switches are essentially a sandwich of thin layers that are bonded together using pressure sensitive adhesives. The layers of a basic membrane switch construction include: a membrane overlay, spacer, printer circuit, rear adhesive, and tail filler. Other electronic components can be implemented, as well, such as discrete LEDs, backlighting sources, and connectors that make membrane switches easy to integrate into other systems or devices. Each layer in a membrane switch assembly serves a different purpose, and custom features require the addition of specialty layers. Depending on the environment and requirements of the application into which the membrane switch plugs into, the construction can vary.
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