14-01-2013, 04:27 PM
Home Appliances Control Using Telephone
Home Appliances Control Using.docx (Size: 286.35 KB / Downloads: 49)
________________________________________
Using this circuit, you can control up to seven electrical appliances through a telephone. The circuit can switch on/off the appliances in two modes. In the first mode, all seven or selected appliances can be switched on individually but switched off simultaneously by pressing a single button on the telephone’s keypad. In the second mode, individual appliances can be switched on and off sequentially.
The circuit is built around dual-tone multiple-frequency (DTMF) IC MT8870 (IC1), 8-bit addressable latch IC CD4099 (IC2), relay driver IC ULN2003 (IC3), voltage regulator IC 7805 (IC4), seven relays and a few discrete components. Connect the appliances to mains through the relays, e.g., bulb (load 1) to relay RL1, fan (load 2) to relay RL2 and so on. Also, assign digit keys to the appliances, say, key 1 to bulb, key 2 to fan, key 3 to television, etc.
Working of the circuit is simple. When you lift the handset from the cradle and press any key (1 through 7), the respective binary output of IC1 goes low while pin 15 goes high. Transistor T1 conducts to enable the latch (IC2), making its corresponding output pin high. The binary outputs of IC1 (Q0 through Q2) are connected to the inputs of IC2 (A0 through A2). IC2 converts the binary input into its decimal equivalent, which is available at its output pins Q1 through Q7. The output of IC2 is fed to relay driver IC3.
GAS LEAkAGE ALARM
________________________________________
LPG gas is supplied in pressurised steel cylinders. As this gas is heavier than air, when it leaks from a cylinder it flows along floor and tends to settle in low spots such as a basement. This can cause fire or suffocation if not dealt with.
Here is a circuit that detects the leakage of LPG gas and alerts the user through audio-visual indications.
Fig. 1 shows the circuit of the gas leakage alarm. The circuit operates off a 9V PP3 battery. Zener diode ZD1 is used to convert 9V into 5V DC to drive the gas sensor module.
The SEN-1327 gas sensor module from RhydoLABZ is used in this circuit. Its output goes high when the gas level reaches or exceeds certain point. A preset in the module is used to set the threshold. Interfacing with the sensor module is done through a 4-pin SIP header.