This document describes a tele remote switch circuit that can remotely control up to 4 devices connected to relay outputs using a telephone's DTMF tones. The circuit uses an AT89C52 microcontroller and MT8870 DTMF decoder chip to detect and decode tones and control the relay outputs. A timer circuit is also described that can be used to set a countdown time to control for how long a connected device remains turned on.

1. Tele Remote Switch With Microcontroller Timer Submitted by:-

2. INTRODUCTION This device connects to the telephone line and can be used to remotely control up to 4 relay outputs using a DTMF telephone . DTMF detection and decoding is provided by IC AT89S52. A timer is constructed to incorporate various facilities like setting the count, start, stop, reset and display. To preset the time for which the connected device would be remained ON.

3. Components Used 9V DC Supply ICs : AT89S52 microcontroller 8870 DTMF(IC1) DM54LS154 / DM74LS154(IC2) CD4049UBC/CD4050BC(IC3) HCF4013(IC4/IC5) Transistor 4 Relay switches Resisters and Capacitors.

4. Description of various components THE ADAPTING 3-TERMINAL VOLTAGE REGULATORS-IC7805 (FOR CONSTANT HIGH VOLTAGE POWER SUPPLIES). Depending upon the current requirement, a reasonable load regulation can be achieved. Rectified and filtered unregulated voltage is applied at Vin and a constant voltage appears between pins 2 and 3 of the voltage regulator. The distribution of two currents in the circuit (IBIAS and ILOAD) is as shown on next slide.

5. Schematic for obtaining low-voltage regulated output using 3-terminal voltage regulators

6. AT89C52 8-bit Microcontroller The AT89C52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, three 16-bit timer/counters, a two-level interrupt architecture, full-duplex serial port, on-chip oscillator, and clock circuitry. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer.

7. DUAL TONE MULTIPLE FREQUENCY (DTMF) DTMF DECODER (MT8870): The DTMF signal is first buffered by an input op-amp . The input stage is followed by a low-pass RC active filter, which performs anti-aliasing function. The time required to detect a valid tone pair, TDP, is a function of decode algorithm, tone frequency, and the previous state of the decode logic. The output corresponding to each key pressed is shown in the truth table :

8. MT8870 OUTPUT TRUTH TABLE FLOW FHIGH KEY TOE Q4 Q3 Q2 Q1 697 1209 1 1 0 0 0 1 697 1336 2 1 0 0 1 0 697 1477 3 1 0 0 1 1 770 1209 4 1 0 1 0 0 770 1336 5 1 0 1 0 1 770 1477 6 1 0 1 1 0 852 1209 7 1 0 1 1 1 852 1336 8 1 1 0 0 0 852 1477 9 1 1 0 0 1 941 1209 0 1 1 0 1 0 941 1336 * 1 1 0 1 1 941 1477 # 1 1 1 0 0 697 1633 A 1 1 1 0 1 770 1633 B 1 1 1 1 0 852 1633 C 1 1 1 1 1 941 1633 D 1 0 0 0 0 ---- ANY 0 Z Z Z Z

9. Circuit for Tele Remote Switch

11. Circuit Description TELEREMOTE CONTROL The DTMF signals on telephone instrument are used as control signals. The circuit uses DTMF DECODER (MT8870 ) ,74154 (4-to-16-line demultiplexer), IC3 (CD4049), flip-flop-1 (F/F-1) and relay RL1 . IC1 decodes this as ‘1010,’ which is further demultiplexed by IC2 (74154). Active low output of IC2, after inversion by an inverter gate of IC3 (CD4049), becomes logic 1.

12. This is used to toggle flip-flop-1 (F/F-1) and relay RL1 is energized. The flip-flop output is used to drive a relay (RL2) which can switch on or switch off the appliance.

13. Working of the circuit A) CONTROL SECTION: - Before anything else, phone line must be ceased on first bell. This ceasing and generation of confirmation tone is done by "Control Section" of circuit. Whenever phone rings, Capacitor C4 is used to pass ring tone effectively.

14. DECODING SECTION: After ceasing of line, the numbers pressed on remote phone's dial pad must be decoded so as to control correspondingly numbered appliances. The DTMF signals from phone line are converted to BCD . The output at pin corresponding to that number goes to logic '0' state while all other outputs remain high . This low output is inverted by IC3 CD4049 to high state, i.e logic '1'.

15. Circuit for Timer:

16. Circuit Description A microcontroller-based industrial timer can be programmed and used as a time totalizer. Performs count-down operation up to 9999 minutes/second . The relay energises as you press the start switch and remains on till the countdown reaches ‘0000. ’ Four tactile, push-to-on switches are used to start/stop, select either minutes or seconds, and set the initial value for count-down operation (using ‘up’ and ‘down’ keys).

17. TESTING THE KIT First of all call the telephone to which kit is connected from any other phone Whenever phone will ring, it will automatically switch to appliance control mode on the first bell. This is made possible by connecting 220 ohms resistance in parallel to phone line, on first bell. A tone will also be heard implying that kit is connected to this phone and you are in appliance control mode.

18. Then pressing '5' followed by number corresponding to appliance's number will switch it on. That is if you want to switch on first appliance press '5' then press '1'. Again pressing '5' and '1' will switch it off. Thus to toggle the state press the same digit again. The phone line will remain in control mode for about 1.5 minutes. Thus you have only this much time period for controlling operations. Else you have to call again. As power-on-reset circuitry is not included here, at each power ON operation, circuit switches to 'Control Mode' initially. Thus after each power ON operation, wait for about 1.5 minutes so that circuit comes to its normal state, and then call from another line.

19. APPLICATION OF THE CIRCUIT Using the teleremote one can remotely control switching of upto five appliances. Just by using dial keypad of remote telephone from where you are calling you can perform on/off operation of the appliances. The range of appliances that are controlled depend upon the person's usage. Room heater, water heater, parking lights, music system or any other electrical/ electronic appliance switching can be controlled once they are connected to kit.

20. CONCLUSION This project shows a tele-remote switch which can control 4 devices connected to it from any distance away. By the application of this project the need of manual control over devices can be reduced. A work can be done from any place on the earth by having a required cellphone and without the actual presence of the person at the devices.

21. References Exploring C for microcontrollers by Jivan S Parab Electronics Projects Vol. 19 www.alldatasheets.com www.howstuffworks.com www.google.com www.wikipedia.com

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