# Circuit explanation for the ultrasonic alarm

Posted on Feb 5, 2014

The alarm detector circuit is different from Ultrasonic Alarm (1). In Ultrasonic Alarm (1), an alarm output is presented when there is a reflected wave from the object in the setup time. At the circuit this time, an alarm is output when no reflected wave from the object is detected in the setup time oppositely. The existence of the reflected wave

in the setup time is detected like Ultrasonic Alarm (1) to do this operation. As for the time setting for 555 timer and so on, please refer to Alarm detector of Ultrasonic Alarm (1). The initialization of the circuit is done with transmission timing pulse (A). C to "L", D and F to "H", G to "L" by which D goes to "H". When a reflected wave is detected within the setup time of 555 timer, C goes to "H". With this, the E shifts to "L". When the E goes "L", F shifts "L" and it is held until the next initialization. G shifts to "H" when D goes "L" with the time-out of 555 timer. However, because F is "L", the alarm output H is held on "H" and an alarm signal isn`t output. The initialization of the circuit is done with transmission timing pulse (A). C to "L", D and F to "H", G to "L" by which D goes to "H". When a reflected wave isn`t detected within the setup time of 555 timer, the change of the E doesn`t occur. It is held on "H". When D goes to "L" by the time-out of 555 timer, G shifts to "H". Because F is held on "H", H shifts to "L" and an alarm signal is output. Even if a reflected wave is detected behind the time-out of 555 timer, because D is held on "L" already, the change of the condition of E doesn`t occur. It is held on "H". So, the alarm output is kept. Alarm detecting circuit is composed of SR-FF (The set and reset type flip-flop circuit) and 555 timer. The reset of SR-FF for alarm detecting which is composed of IC8...

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