This touch-sensitive help board is very useful when the elderly, the sick and the sick need someone to help. The helper only needs to touch the help board installed on hand, and the touch-sensitive circuit will automatically send out a help signal. Attract other people's attention and get help in time (see photo). The yellow LED3 on the display board indicates that a call for help occurs, the red LED2 indicates that immediate assistance is needed, and the green LED1 indicates the standby state after the circuit is connected.
When the help board is touched by a person, the body charge causes the transistor T1 to be positively biased and turned on. After being turned on, it outputs a negative pulse to trigger the chip 7555 (IC1), and the IC1 output becomes high for a certain period of time.
The rising edge of the output pulse of IC1 triggers HEF4017 (IC2) again. IC2 is a decimal counter with ten decoding outputs. During the period when the counter is low, its output terminal advances one by one according to the rising edge clock pulse received by its clock input pin.
The reset pin resets IC2 when it receives a rising edge signal.
When IC2 receives a clock pulse from IC1 through diode D1 and resistor B2, its Q1 output becomes high, and tune generator IC3 receives positive power through diode D2 and resistor R6, while yellow LED3 emits light. The tune sent from IC3 is amplified by the transistor T2 and then released from the speaker LS1.
After IC2 receives the second pulse, its Q2 output becomes high, at which time the call for help stops. The red LED2 glows, indicating that immediate assistance is needed. Capacitor C2 can prevent accidental false triggering of the alarm circuit.
The Q3 output pin of IC2 is connected to its reset pin, so it resets when IC2 receives the third pulse.
To sum up: call for help when the first touch; stop the call when the second touch, and make the red LED2 of the immediate rescue light turn on; the third touch is to light the green LED1 after getting the rescue. Therefore, if the red LED2 is always on, it means that although the helper has issued a help call, no one pays attention to the helper.
The touchpad can be made of 15cm & TImes; 15cm aluminum foil or copper foil board, and connected to the circuit with a 1m long plastic wire.
The circuit is powered by a 9V battery, and an AC adapter with a 9V DC output can also be used.
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