555 simple sickbed calling device circuit

Published:2011/5/25 1:35:00 Author:TaoXi | Keyword: simple sickbed, calling device | From:SeekIC

As the figure 16-8 shows, the controllable multivibrator is composed of the 555 and R1，R2，C1, the circuit start-up depends on the electric potential of the reset port pin-4. Whenyou press any one swith of the K1～K4, pin-4 has the high electric potential, 555 starts working to send out the sound and light alarm signals. The oscillation frequency f=1.44/(R1+2R2)C1, it is about 1000Hz.



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