Circuit design of membrane switch

The design of membrane switch circuit can be roughly divided into two types. One is the common bus method

The design of membrane switch circuit can be roughly divided into two types. One is the common bus method, in which one end of a contact of each membrane switch is directly connected by a bus; The other end of the membrane switch leads out several independent circuits, which is common in the mechanical discrete membrane switch. Its advantage is that each switch directly controls a special function. In this case, the obtained signal does not need to improve the decoding in the post circuit. However, in general, membrane switches are only suitable for occasions with few function keys. When the number of switches increases, it is not favorable enough. At the same time, the number of leads will increase a lot, and the total number of leads is greater than the number of switches.

The other is the X-Y moment arrangement method. As shown in Figure 2, it consists of "rows" and "columns" to form a matrix. In the direction of the same row (i.e. X direction), regardless of the number of switches, one end of the switch is led out by a common line; Similarly, in the direction of the same column (i.e. Y direction), regardless of the number of switches, the other end of the switch is connected and led out by a common line. In this way, the arrangement of the matrix can form the X-Y combination of any switch. Before it can control each special function, it is often necessary to set the decoding in the post circuit. However, it is not difficult in the logic circuit.

The design of membrane switch circuit, as a guide document for process manufacturing, should strive to design the matrix, and the membrane switch can be consistent with the actual key position. This can reduce the trouble of rewiring during production; At the same time, it is also conducive to inspection and avoid errors. The best expression method is to mark the function content of each key in the matrix directly when drawing the circuit diagram. The membrane switch is consistent with the actual position of the key, and then the leads are numbered in the order from left to right, so that it is clear at a glance and there is no need to list the wiring relationship table.