Archive for April, 2009
2009 April 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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LED circuit
Apr 26th
Some LED circuits explained examples from various projects: flashing LEDs, 220V LEDs and more. We start by showing you the LED circuit in series with a resistor. You must make some calculations to figure out the resistor value, depending on voltage power supply, LED voltage drop and desired current. (more…)
Ultrasonic pest repeller
Apr 25th
There are many ultrasonic pest repellers available on the market but a major drawback is that their power output is low and their effectiveness suffers. The electronic pest repeller generates powerful ultrasonic signals to repel pests. (more…)
Electronic doorbell circuit
Apr 25th
This simple and cost-effective ding dong electronic doorbell circuit is based on IC 8021-2. The IC has an in-built circuitry to produce ding dong sound each time its pin 3 is pulled low. The sound is stored in the IC as bits, as in a ROM. The sound output from the IC can’t however drive a speaker directly, as this puts strain on the device. (more…)
Smoke detector circuit
Apr 25th
This home smoke detector circuit warns the user against fire accidents. It relies on the smoke that is produced in the event of a fire and passes between a bulb and an LDR, the amount of light falling on the LDR decreases. This type of circuit is called optical smoke detector. Do not use it as a home smoke detector it’s jus for electronic projects. (more…)
Fire Alarm Circuit
Apr 25th
In this fire alarm circuit project, a thermistor works as the heat sensor. When temperature increases, its resistance decreases, and vice versa. At normal temperature, the resistance of the thermistor (TH1) is approximately 10 kilo-ohms, which reduces to a few ohms as the temperature ncreases beyond 100°C. The circuit uses readily available components and can be easily constructed on any general purpose PCB. Check out the fire sensor circuit. (more…)
Sound activated lights
Apr 25th
This sound activated lights circuit turns a lamp ON for a short duration when the dog barks (or a relatively strong sound) giving an impression that the occupants have been alerted. (more…)
AM transmitter
Apr 25th
This low-cost AM transmitter is tunable from 10 to 15 MHz with the help of ½J gang condenser VC1, which determines the carrier frequency of the amplitude modulation transmitter in conjunction with inductor L1. The frequency trimming can be done with VC2. The carrier is amplified by transistor T4 and coupled to RF amplifier transistor T1 BD677 through transformer X1. (more…)
FM Radio Transmitter
Apr 23rd
A simple fm radio transmitter circuit which covers frequencies from 88 to 108 MHz. It is built with 3 transistors: BC109, BFR91A and BFR96S. It is quite stable and the output power is around 200 mW.
The first stage in a mic amplifier but if you connect this radio transmitter directly to an audio source you can remove this stage and connect the audio signal to R5. (more…)
BF420
Apr 22nd
BF420 is a NPN high-voltage transistor in a TO-92 plastic package and it’s PNP complements are BF421 and BF423. (more…)
BB131 datasheet
Apr 21st
BB131 is a variable capacitance diode, fabricated in planar technology, and encapsulated in the SOD323 very small plastic SMD package. (more…)
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