Wednesday, 13 July 2011
Pest Chaser
Keep Mosquitoes and Insect pests away from your premises using this Ultrasonic Pest Chaser. Its frequency can be varied from 10 KHz to 90 KHz so that most of the insect populations can be repelled.
Most of the animals including insects can hear ultrasound which is annoying to them. So they avoid such situations. This Ultrasound generator uses the popular CMOS IC CD 4047 to generate Ultrasound. This IC is the precision Monostable / Astable IC and its oscillating frequency can be changed using C2 and VR1. In this design it is used as an Astable Multivibrator. With the given values of C2 and VR1, the output frequency can be adjusted from 10 KHz to 90 KHz. Most of the animals respond to 22 KHz to 60 KHz. Mosquitoes respond to 38 KHz. The ultrasound vibrations from the outputs of IC will be amplified by a set of Push-Pull amplifier T1 through T4.A Piezo tweeter is used as sound generator because the piezo element is designed to generate KHz signals. The circuit requires 9 to 12 volt supply which can be obtained from a PP3 battery.
Note: Response to the circuit should be tested through observation. Response depends on the number of insects, their behavior etc. Try different frequencies and find the suitable frequency of a particular insect group.
FIRE ALARM
This is the circuit of a Fire sensor that produces loud beeps when it detects heat from fire. The circuit uses a Thermister as fire sensor. Thermister is a special kind of resistor and its resistance depends on the temperature. In cold, Thermister offers high resistance and its resistance decreases to a few ohms when the temperature near it increases.
The Thermister is connected to the points A and B. When the temperature is normal, it offers high resistance so that it will not conduct. This gives a high voltage to the pin 12 of IC1. It is a binary counter that becomes active only when its reset pin 12 is low. So in the standby state, IC will not work and alarm generator remains silent. Variable resistor VR1 adjusts the sensitivity of the Thermister at the particular temperature level. When there is fire in front of the Thermister, the temperature rise caused by the fire reduces the resistance of the Thermister and it becomes conducting. This takes the reset pin 12 of IC1 to ground and it starts oscillating. The oscillations of IC1 generate beeps through the buzzer. LED also blinks indicating the fire. VR2 can be adjusted to get slow to fast beep rates.
Components Required
R1 1M, R2 100 Ohms VR1 100K, VR2 1M presets C1 0.22 IC1 CD 4060 Buzzer, D1 LED 16 pin IC base Thermister Battery snapper PCB 9 volt PP3 battery
Assembling and Testing
Assemble the circuit carefully on the PCB. Solder Resistors first and then IC base and Presets. Then solder other components. Observe the polarity of Buzzer and Battery snapper. A switch can be connected between the PCB and one of the batter snapper wire. After completing the circuit, fix IC in the socket observing its orientation similar to IC base. Connect battery. If buzzer sounds, adjust VR1 to set the sensitivity of Thermister so that the Buzzer just stops sounding. If not adjust VR1 again. Show a lighted match stick near the Thermister (not on it). Buzzer should sound. This indicates fire.
WHITE LED LAMP
This is the simple version of a white LED lamp that can be directly powered from mains.
It can give ample light even for reading purpose. Capacitor CX along with diodes D1 through D4 forms the AC step down circuit. CX reduces high voltage AC from mains to a low voltage AC which is rectified by the diodes D1-D4. Capacitor C1 removes ripples from AC so that low voltage DC is available to power the LEDs.CX is the X rated AC capacitor that reduces AC voltage through capacitive Rectance property. Resistor R1 is very important to remove the stored voltage from CX when power is switched off. This prevents lethal shock. Resistor R2 limits the inrush current. More LEDs can be added by reducing the value of R2.
Shock Hazard
Since the circuit is directly connected to mains, take utmost care to avoid shock. No components should be touched when it is connected to mains. Construct this circuit only if you are experienced in handling high voltage AC.
38 KHz Astable Multi vibrator
The circuit is a simple IR transmitter operating in the 38 KHz, the frequency of most IR sensors used in TV. The Atable multivibratior built around the popular IC 555 generates output pulses with a frequency of 38 KHz. The output frequency can be set by VR exactly to 38 KHz.
Tuesday, 12 July 2011
Mobile charger from bike
This is the simple and easy way to tap current from a Motor Bike battery to charge the Mobile Phone. Most of the Mobile Phone battery pack has three 1.2 volt cells making the voltage to 3.6 volts. For fast charging of the battery pack, each cell requires more than 1.2 volts and sufficient current. This circuit can deliver 5 volts at 300 mA to charge the battery quickly. The circuit is Voltage and Current regulated and with Polarity and Surge protection components.
The circuit uses a Positive Voltage regulator IC 7805 to give 5 volt regulated output. The components around IC1 are meant for protecting the IC so as to give smooth output power. Zener diode ZD act as the Input Surge protecting diode. It provides 7.2 volts to the input of the regulator IC from the 12 volt bike battery. Diode D1 is the Output Surge and Input Short protecting diode.
When a surge voltage exceeding maximum voltage rating of the regulator is applied to the input or when a voltage in excess of the input voltage is applied to the output, the regulator will be destroyed. If the input terminal shorts with the ground, the output voltage increases above the input voltage(ground potential)and the charge in the capacitor connected to the output flows into the input side which is also fatal to the regulator. Both these situations can be avoided by using the Zener at the input and the diode D1 across the regulator. Capacitor C1 and C2 provide stability to the regulator and these should be soldered close to the legs of the regulator. Capacitor C3 act as a buffer to give constant voltage in the output.
7805 IC can tolerate maximum 35 volts and its current rating is 1 Amps maximum. Resistor R1 restricts the charging current to around 330 mA as per the Ohms law. Even if the current is low, charging process will not be affected. Slow charging with 80 to 100 mA current is generally advised. But in case of an emergency, quick charging can be done with high current
Assemble the circuit on a Perf board and enclose in a small case that can be fitted near the Bike battery. Use suitable pins to connect with the Mobile phone. Charging current can be tapped from the battery using Alligator Clips. Before using the circuit, double check the connections especially the polarity of connectors and measure output voltage and current using a Digital Multi Meter. The same circuit can be used for charging Mobile battery from 12 volt Car battery or from a 12 volt Solar panel.
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