The Gentle Touch Circuit Diagram

Consumer appliances these days hardly ever have a proper mains switch. Instead, appliances are turned on and off at the touch of a button on the remote control, just like any other function. This circuit shows how a device (as long as it does not draw too high a current) can be switched on and off using a pushbutton. The approach requires that a microcontroller is already available in the circuit, and a spare input port pin and a spare output port pin are required, along with a little software. When power is applied T1 initially remains turned off. When the button is pressed the gate of T1 is taken to ground and the p-channel power MOSFET conducts. The microcontroller circuit is now supplied with power. Within a short period the microcontroller must take output PB1 high. This turns on n-channel MOSFET T1 which in turn keeps T1 turned on after the push-button is released.

Now the microcontroller must poll the state of the push-button on its input port (PB0) at regular intervals. Immediately after switch-on it will detect that the button is pressed (a low level on the input port pin), and it must wait for the button to be released. When the button is next pressed the device must switch itself of f: to do this the firmware running in the microcontroller must set the output port pin to a low level. When the button is subsequently released T1 will now turn off and the supply voltage will be removed from the circuit.

The circuit itself draws no current in the off state, and for (rechargeable) battery-powered appliances it is therefore best to put the switch before the voltage regulator. For mains-powered devices the switch can also be fitted before the voltage regulator (after the rectifier and smoothing capacitor). Since there is no mains switch there will still be a small standby current draw in this case due to the transformer. Be careful not to exceed the maximum gate-source voltage specification for T1: the IRFD9024 device suggested can withstand up to 20 V. At lower voltages R2 can be replaced by a wire link; otherwise suitable values for the voltage divider formed by R1 and R2 must be selected.

Circuit diagram:

 The Gentle Touch Circuit Diagram

The author has set up a small website for this project at http://reweb.fh-weingarten.de/elektor, which gives source code examples (which include dealing with pushbutton contact bounce) for AVR microcontrollers suitable for use with AVR Studio and GNU C. Downloads are also available at http://www.elektor.com.

Fire Sensor Pyroelectric Circuit Diagram

This is the  Fire Sensor Pyroelectric Circuit Diagram. Here is an ultra-sensitive fire sensor that exploits the direct piezoelectric  property  of  an ordinary piezo element to detect fire. The lead  zirconate  titanate  crystals  in the piezo element has a property to de-form and generate an electric potential plifier with gate protected p-channel.  MOSFETs in the inputs. It has high speed  of  performance  and  low  input current requirements. There are two inputs—the non inverting input (pin 3) connected to the piezo element through diode D7 (OA71) that carries the volt-age signal from the piezo element and the inverting input (pin 2) that gets a momentarily changes the voltage level at pin 3 of IC1 and its output swings high. Transistor T1 conducts taking the reset pin 12 of IC2 to ground. IC2 is now enabled and start oscillating. With the shown values of the oscillating components C3 (0.22) and R8 (1M), when heated, thus converting the piezo element into a heat sensor. 

Pyroelectric Fire Sensor -Circuit-Diagram

 

The circuit we  have  described  here  is  very  sensitive. It gives a warning alarm if the room temperature increases more than 10 degree Celsius. The entire circuit is divided  into  two  section—the  sensor and the power supply section. Sensor side circuit. Fig. 1 shows the fire sensor circuit. The front end of the circuit has a sensitive signal amplifier built around IC1 (CA3130). It gives a  high  output when the  temperature near the piezo element increases. IC CA 3130 is a CMOS operational am-preset  volt-age through VR1.By adjusting VR1, it is easy  to set the reference voltage level at pin 2. In normal condition, IC1 gives a low output and the remaining circuitry will be in a standby state. Capacitor C2(10P) keeps the non-inverting in-put of IC1 stable, so that even a slight change in voltage  level  in  the  inputs can change the output to high. 

Normally, IC1 gives a low output, keeping transistor T1 non-conducting. Reseting pin 12 of IC2 (CD4060) connected to the collector of transistor T1 gets a high voltage through R6 and IC2 remains disabled. When the piezo element gets heat from fire, asymmetry in its crystals cause a potential change, enabling capacitor C2 to discharge. It the first output (Q3) turns high after 4 seconds and a red LED starts flashing. If the heat near the piezo persists, Q7 (pin 14) output of IC2 becomes high after  1  minute,  and  the  alarm  starts beeping. If heat continues, Q9 (pin15) turns high after four minutes and turns on the relay driver transistor T2. At the same time, diode D8 conducts and IC2 stops oscillating and toggles.The  solenoid  pump  connected  to the N/O (normally opened) contact of the relay starts spraying the fire-ceasing foam or water to the possible sites of fire.

 Power Supply With Battery Backup  Circuit Diagram

Power  supply  circuit. Power sup-ply section (Fig. 2) comprises a 0-12V, 1 A step down transformer with a standard full wave rectifier formed by D1 through D4 and filter capacitor C1. A battery backup is provided if the mains supply cut-off due to short-circuit and fire. A 12V, 4.5 Ah rechargeable battery is used for backup to give sufficient current to the solenoid pump. 

When mains power is available, diode D5 forward biases. It provides power to the  circuit  and  also  charges  the  bat-tery through resistor R2 and it limits the charging current to 120 mA. When power fails, diode D5 reverse biases and diode D6 forward biases, giving instant backup to the circuit. LED1 indicates  the  availability  of  mains power.Assemble the circuit on a common PCB and enclose it in a suitable case. Connect the piezo element to the circuit using thin plastic wire. Glue the flat side of the piezo element on a 30x30 cm aluminium sheet to increase its sensitivity. Fix the sheet with the piezo  sensor  to  the  site  where  protection is needed. The remaining circuit can be fixed in a suitable place. If only the alarm generator is needed, omit the relay driver section. 

Author :D. Mohan Kumar - Copyright : EFYMag

Proximity Detector Circuit Diagram

This is the simple Proximity Detector Circuit Diagram. This proximity detector is constructed using an infrared diode detector. Infrared detector can be used in various equipment such as burglar alarms, touch free proximity switches for turning on a light, and solenoid-controlled valves for operating a water tap. Briefly, the circuit consists of an infrared transmitter and an infra-red receiver (such as Siemens SFH506-38 used in TV sets).

  The transmitter part consists of two 555 timers (IC1 and IC2) wired in astable mode, as shown in the figure, for driving an infrared LED. A burst output of 38 kHz, modulated at 100 Hz, is required for the infrared detector to sense the trans mission; hence the setup as shown is required.  To save power, the duty cycle of the 38kHz astable multivibrator is maintained at 10 per cent.  The receiver part has an infrared detector comprising IC 555 (IC3), wired for operation in monostable mode, followed by pnp transistor T1. Upon reception of infrared signals, the 555 timer (mono) is turned  ‘on’ and it re-mains  ‘on’ as long as the infrared signals are being received.

Proximity Detector Circuit Diagram:
 

Proximity Detector Circuit Diagram

 

When no more signals are received, the mono goes  ‘off’ after a few seconds (the delay depends on timing resistor-capacitor combination of R7-C5). The de-lay obtained using 470kilo-ohm resistor and 4.7µF capacitor is about 3 seconds. Unlike an ordinary mono, the capacitor in this mono is allowed to charge only when the reception of the signal has stopped, because of the pnp transistor T1 that shorts the charging capacitor as long as the output from IR receiver module is available (active low).  This setup can be used to detect proximity of an object moving by. Both transmitter and receiver can be mounted on a single breadboard/PCB, but care should be taken that infrared receiver is behind the infrared LED, so that the problem due to infrared leak-age is obviated.  

An object moving nearby actually reflects the infrared rays from the infrared LED. As the infrared receiver has a sensitivity angle of 60o, the IR rays are sensed within this lobe and the mono in the receiver section is triggered. This principle can be used to turn ‘on’ the light, using a relay, when a person comes nearby. The same automatically turns  ‘off’ after some time, as the person moves away. The sensitivity depends on the current limiting resistor in series with the infrared LED. It is ob-served that with in circuit resistance of preset VR1 set at 20 ohms, the object at a distance of about 25 cms can be sensed.  This circuit can be used for burglar alarms based on beam interruption, with the added advantage that the transmitter and receiver are housed in the same enclosure, avoiding any wiring problems.