Telephone remote control circuit

The telephone remote control circuit uses the ringing of the telephone as the remote control identification signal, so there is no need to pick up the phone and no phone charges are charged. The remote control circuit is reliable and
easy to operate. Settings for this circuit: The circuit can only be activated if the ringing signal is input more than 5 times within 2nun; and the interval between each ringing signal
must be more than 5s, and the continuous ringing signal circuit can only be regarded as a valid ringing signal once Make a count. Because few people dial
the same phone more than 5 times on 2nun , and the interval between each call should be greater than 5 seconds. This greatly improves the reliability of the remote control and can effectively avoid
malfunctions caused by ringing from outside calls. At the same time, it will not affect normal calls, and there is no need to change the phone line. It can be easily
operated through the redial key.
    As shown in Figure 18-25, the circuit consists of ringing strobe, pulse width strobe, counter, T flip-flop, time-limited reset and other circuits. Connect terminals a and
b to the telephone line. Because of capacitance C. DC blocking effect, when in standby, the voltage at both ends of G is 0, and the optocoupler is cut off. The rear circuit is
in standby mode.
    When the ringing signal arrives, it is coupled by G, coupled by the optical coupler after bridge rectification and capacitor filtering, and passed by R. , G pulse
width gating circuit. When there is a ringing signal, the optocoupler turns on and charges C3 quickly; when the ringing signal disappears, the charge on G is discharged through R4
. It returns to low level after about Smin, forming a pulse output to the counting input end (@ pin) of the ringing signal counter IC1. It can be seen
that the circuit can only recognize the ringing interval if it is more than 5s. For continuous ringing signals with an interval less than 5s, the circuit can only
count it as a valid ringing signal once. When counter IC1 receives 5 pulses, the ① pin of Q5 becomes high level and is output to the pulse input terminal @ pin of IC3, causing
the state of the T flip-flop output terminal composed of T flip-flop circuit IC3 to flip, causing the relay to action to complete the on/off control of electrical appliances.
    The time-limited reset circuit IC2 and peripheral components constitute a time-limited reset circuit. The time-limited time is determined by wind and 0, and is set to 2nun in the figure. When the first ringing
signal arrives, the ◎ pin of IC1's Ql becomes high level, and the transistor VT1 inverts the phase, causing the ② pin of IC2 to become low level and triggered, and its ③ pin outputs high level; through Yan and VD2 charge the capacitor G. When the delay ends, pin ③ becomes low level. VT2 changes from cut-off to conduction, and is powered by electrical density G. The transistor collector outputs a high level at this time, and is added to the reply terminal @ pin of Icl to reset it to zero. It enters standby mode again . - -The     button in the circuit is used to set the initial state of the relay. Each time it is pressed, the state of the relay changes. Then the relay status can be changed through telephone remote control to complete the on/off control of electrical appliances.