What is the basic properties of the membrane switch?
Membrane switch with simple structure, good appearance, good sealing, long service life (up to more than 1 million times), widely used in electronic devices of all kinds of microcomputer control instruments. Membrane switch according to different base material can be divided into two categories, soft and hard; Press button type can be divided into two classes; touch key, no touch key According to the panel structure can be divided into two categories, flat type, concave and convex type.
Membrane switch determines the structure characteristics of low working voltage (< 30 v), carrying small dc current (< 300 ma) and no self-locking function, can not directly control the load circuit, membrane switch for light touch type is normally open to switch, switch normally two contact shows off state, when the external force on membrane switch contact, instantaneous through two normally open contacts.
Membrane switch used in digital circuit, attention should be paid to overcome dithering phenomenon. General method is to join in the circuit and monostable delay circuit, shaping circuit, to overcome membrane switch on and off in an instant jitter occurred due to unstable state, can also be between the switch contact with the ground and a 0.1 uF filter capacitor to eliminate jitter.
External force disappears, membrane switch contact to restore normally open state, and therefore cannot be used to alternate or interlock switch; Membrane switch cannot be directly meet in the middle of 220 v circuit, in use should be made to match the auxiliary circuit, trigger signal (elv) controlled by the membrane switch to control the auxiliary circuit, the auxiliary circuit control main circuit (high voltage), realize the function of the weak current control high voltage.