Archive for January, 2009
2009 January circuits - related electronic projects and circuit diagrams (schematics), this helps you finding desired informations and facilitates your site navigation through all articles database.
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PWM DC power controller
Jan 31st
This DC power supply controller is controlled by pulse width modulation PWM, generated by the circuit around timer IC2 7555 according to the formula: Duty cycle = ((R1 + (VR1/2)/(R1+R2+VR1)) x 100% Diode D1 is used to bypass resistor R2 and half the effective resistance of the “lower” section of VR1, allowing the duty cycle to be varied from 0.01% to 99.9%. Read the rest of this DC power controller circuit. (more…)
Dual-mode battery charger
Jan 31st
There are two main types of battery charger – constant voltage and constant current. Both have their advantages and disavantages. For constant voltage, the battery cannot be overcharged but the charging rate is slow. Constant current mode can charge batteries more swiftly but there is the danger of overcharging them. The dual mode battery charger circuit featured here was designed to combine both modes, but without their disadvantages, for use with a 6V sealed lead-acid battery.
Read the rest and view the dual mode battery charger circuit (more…)
Simple metal detector circuit
Jan 31st
The metal detector circuit shown here must represent the limits of simplicity for a metal detector, yet the design works surprisingly well. It uses just one 40106 hex Schmitt inverter IC, a capacitor and a search coil – and of course the batteries. A lead from IC1b pin 4 needs to be attached to a medium wave radio aerial, or it should be wrapped around the radio. It can be used even like those hand held metal detectors. (more…)
Quality FM transmitter
Jan 30th
This house FM transmitter for your stereo or any other amplifier provides a good signal strength up to a distance of 500 meters with a power output of about 200 mW. It works off a 9V battery.
The audio-frequency modulation stage is built around transistor BF494 (T1), which is wired as a VHF oscillator and modulates the audio signal present at the base. Using preset VR1, you can adjust the audio signal level. (more…)
Remote audio level indicator
Jan 29th
The normal level-indicator circuits which are available in the market require connections to be made to the output of the player, which may not be easily accessible. The audio level indicator circuit described here removes this restriction as it may be placed close to the player’s speakers and yet the desired effect can be realised. (more…)
Dog repellent
Jan 28th
The electronic dog repellent circuit diagram below is a high output ultrasonic transmitter which is primarily intended to act as a dog and cat repeller, which can be used individuals to act as a deterrent against some animals. It should NOT be relied upon as a defence against aggressive dogs but it may help distract them or encourage them to go away and do not consider this as an electronic pest repeller. (more…)
Lightning detector
Jan 27th
This lightning detector circuit is a very sensitive static electricity detector that can provide an early warning of approaching storms from inter-cloud discharge well before an earth-to-sky return strike takes place. An aerial (antenna) formed of a short length of wire detects storms within a two mile radius. The circuit emits an audible warning tone from a piezo buzzer, or flashes an LED for each discharge detected, giving you advance warning of impendig storms so that precautions may be observed. (more…)
Luggage, bike security alarm
Jan 26th
This luggage or bike alarm can be used while travelling by trains or bus and we generally lock our luggage using a chain-and-lock arrangement. But, still we are under tension, apprehending that somebody may cut the chain and steal our luggage. Here is a simple circuit to alarm you when somebody tries to cut the chain. (more…)
Cell phone detector
Jan 25th
This handy cell phone detector, pocket-size mobile transmission detector or sniffer can sense the presence of an activated mobile cellphone from a distance of one and-a-half metres. So it can be used to prevent use of mobile phones in examination halls, confidential rooms, etc. It is also useful for detecting the use of mobile phone for spying and unauthorised video transmission. (more…)
Simple code lock
Jan 25th
This simple code lock circuit described here is of an electronic combination lock for daily use. It responds only to the roght sequence of four digits that are keyed in remotely. If a wrong key is touched, it resets the lock. The lock code can be set by connectiong the line wires to the pads A, B, C and D in the figure. For example, if the code is 1756, connect line 1 to A, line 7 to B, line 5 to C, line 6 to D and rest of the lines-2,3,4,8 and 9 to the reset pad as shown More >
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