Touch type small capacitance long timer

1. Touch-type small capacitance long-term timer Here we introduce a novel touch-type small capacitance long-term timer. Because it cleverly sets the level of the control terminal ⑤ of the time base circuit, the data can be obtained when the timing capacitance value is not large. hour timer. Another feature of this circuit is that it adopts touch control mode. As long as your finger touches the touch electrode pad lightly, the timer can be triggered to work. [Circuit Principle] The circuit of the touch-type small capacitance long-term timer is shown in Figure 10-l. The circuit is mainly composed of a 555 time base integrated circuit, a touch electrode sheet and a power circuit. The time base integrated circuit 555 forms a monostable trigger. Normally, the time base circuit is in a stable state. The output terminal ③ pin outputs a low level, the relay K does not operate, its normally open contact k-1 is open, and the output socket XS is not sent to the outside world. electricity. When the socket XS is required to send power to the outside, just touch the electrode piece M with your hand. The clutter signal induced by the human body will be coupled by Cl and rectified by VDl to obtain a negative pulse at the trigger terminal ② pin of the time base circuit. The time base circuit will immediately flip over and enter the temporary state. state, at this time, the output terminal ③ pin outputs high level, the relay K is powered on, its normally open contact k-1 is closed, the socket XS sends power to the outside, and the household appliances plugged in XS such as desk lamps, electric fans, etc. are powered Work. At the same time, the discharge tube inside the time base circuit is turned off, pin ⑦ is left floating, and the power supply charges the timing capacitor C2 through the potentiometer RP, so that the level of the threshold terminal (6) pin of the time base circuit continues to increase. Usually when the time base circuit is in monostable operating mode, its control terminal ⑤ pin is left unconnected or connected to ground through a capacitor. The ⑤ pin of the control terminal is connected to a voltage divider composed of three internal resistors in the internal circuit, and its level is fixed at 2/3VDD. When the voltage at both ends of C2 is charged to the ⑤ pin level, which is 2/3VDD, temporarily state ends, the circuit returns to steady state. This circuit cleverly adds a diode VD2 between pin ⑤ of the time base circuit and the positive terminal of the power supply, so that the level of pin ⑤ rises from 2/3VDD to VDD-0.65V, which is only 0.65V lower than the power supply voltage. Therefore, the circuit does not flip until the voltage at both ends of C2 is charged to VDD-0.65V, thus greatly extending the charging time, that is, the timing time. Therefore, C2 does not need to use a large-capacity capacitor to obtain long-term timing. When the base circuit returns to the steady state, the output terminal ③ pin outputs a low level, the relay K loses power and is released, and XS stops sending power to the outside. At the same time, the internal discharge tube of the time base circuit is turned on, and the ⑦ pin is short-circuited to the ground through the internal discharge tube. The capacitor C2 is discharged to prepare for the next scheduled charge. LED is the indicator light for the external power supply of the socket XS. When the LED lights up, it means that the circuit is in a scheduled working state and the XS sends power to the outside. When the LED goes out, it means that the timing is over and the XS stops sending power to the outside. Rp is the timing time adjustment potentiometer. Adjusting the size of Rp can change the length of the timing time. VD4 to VD7 and T form a power circuit to provide an operating voltage of about 10V for the time base integrated circuit. [Component selection] A uses time base integrated circuits such as NE555, μ A555, SL555, etc. VDl-VD3 can use silicon switching diodes such as 1N4148 type, and VD4 to VD7 can use silicon rectifier diodes such as 1N4001 type. The LED can be an ordinary red light-emitting diode. Rp can use WH5 type small synthetic carbon film potentiometer, R1 is RTX-1/8W type carbon film resistor. Cl uses CTl type porcelain capacitors, and the remaining capacitors can use CDll-16V type electrolytic capacitors. T is a 220V/9V, 8VA small power transformer. K can be used with small electromagnetic relays such as JRX-13F, DC9V or JZC-22F, DC9V type. [Production and use] Figure 10-2 is the printed circuit board diagram of the timer. The printed circuit board size is 80×50 (mm). The finished printed board should be installed in a self-made plastic box. The touch electrode sheet M and the rotary axis and dial of the potentiometer Rp should be set on the box surface, and the socket XS should be set on the side of the box. The timing time of this timer mainly depends on the values ​​of potentiometer Rp and capacitor C2. When C2 takes the value of 47μF and Rp takes the value of 510kΩ, the maximum timing can be 120s; if RP takes the value of 2MΩ, the maximum timing can be 625s. If the capacity of C2 is further increased, the timing time will be longer. Finally, through the method of experiment, the timing time is marked on the dial of Rp. When using it in the future, just adjust the RP to the predetermined timing time, touch the electrode sheet M, and the timer will start working.