Fan sensor. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches
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During the hot summer season, sales of fans in stores increase significantly. Simple fans that flood the market have conventional control functions (on-off) and several rotation speeds. By adding a simple electrical circuit to such a fan, you can control its activation using a sensor and not worry about turning it off, since the timer provided in the circuit will automatically turn off the fan after a specified time.
The diagram contains a minimum of details. The use of MOS chips allows you to power the circuit even with an unstabilized voltage within 8...15 V and not worry about electrical noise. A special feature of the device is the use of the K561IE16 counter - a 14-bit asynchronous counter with serial transfer. It allows you to program the load switch-off delay time in the range from 2 to 160 minutes (for the ratings of RC elements indicated on the diagram). As stated in the description, the counter is reset to zero by applying a positive pulse with a duration of at least 550 ns to the R input. The contents of the counter are increased by the negative edge (cut) of the pulse arriving at input C. The counter outputs are made from 1, 4...14 bits.
After power is applied to the circuit, thanks to the R4-C3 chain, due to which a low level is formed at the input of element DD1.2 while capacitor C3 is charging, and at the output DD1.2. accordingly, high, counter DD2 is set to zero. At a low logical level at input R, counter DD2 counts pulses with a frequency of 1 Hz, which are generated by multivibrator DA2 (timer KR1006VI1 in self-oscillation mode).
The DA1 chip implements a sensitive sensor. In the initial state, output DA1 is a low logical level (logical "0"). When you touch the E1 sensor plate, which can be made, for example, in the form of a small current-conducting pad (nameplate) on an insulated fan housing, a logical “1” signal appears at output DA1. The peculiarity of this inclusion of DA1 is that the sensitive trigger input (pin 2) of the KR1006VI1 microcircuit even reacts to the touch of a person wearing gloves (through clothing, etc.). The length of the wire from the E1 sensor to the DA1 input should be minimal. Stable operation of the sensor node was observed with a conductor length of no more than 15 cm. The duration of the output pulse DA1 is determined by the ratings R2 and C2 and in this version is 2 s. This time is quite enough to, after double inversion by elements DD1.1 and DD1.3, open transistor VT1 and turn on relay K1, whose contacts K1.1 switch fan M1. At the same time, a positive pulse (after inversion by element DD1.2) resets counter DD2.
Programming the required shutdown delay of the node is carried out by connecting a jumper to the corresponding output of the counter DD2 with the input of the logical element DD1.4.
With the jumper indicated in the diagram, the maximum time delay is 160 minutes. After counter DD2 counts the number of clock pulses corresponding to the given delay, the output of DD2 is set to “1”, which is inverted by element DD1.4 and stops the multivibrator DA1. At the same time, this “1”, since at the other input of the element DD1.3 there is also a “1” from the output of DD1.1, forms a “1.3” at the output of DD0. which leads to the closing of the transistor and disconnection of the relay and load. The circuit remains in this state until the next impact on the E1 sensor.
Author: A.Kashkarov, St. Petersburg
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