The STEAM Spot

   Phone FM Transmitter Component List: T1 - BC559 Transistor L1 - 4.5 Variable Coil LED - Red LED D1-D4 - 1N4004 Diode C1 - 330pF Capacitor C2 - 470pF Capacitor C3 - 12pF Capacitor C4 - 25pF Capacitor R1 - 12K Resistor R2 - 200 Ohm Resistor R3 - 1K Resistor ANT - 10cm / 4" wire    Technical Specifications: Voltage Supply:  Powered by the telephone line Frequency:  88 to 92MHz Transmission Range:  100m / 300 feet Phone FM Transmitter This Phone FM transmitter connects in series to your telephone line and transmits the telephone conversation over the FM band when you pick up the telephone handset. Transmitted signal can be tuned by any FM receiver. The circuit includes an "On Air" LED indicator and also provides a switch which can be used to turn off the transmitter. A unique feature of the circuit is that no battery is needed to operate the circuit since power is taken from the telep...

Automatic Fan Controller Circuit This circuit will turn on/off 12V DC fan or CPU fan when temperature above normal temperature.You can set turn on temperature by adjust VR1. This circuit use an NTC (Negative temperature coefficient)which is a thermistor is one in which the zero-power resistance decreases with an increase in temperature. So If temperature increase the voltage at pin 3 on LM311 will decreased .The resistance of NTC is about 10K at 25'c. VR1 should be multi-turn potentiometer type such 10K/25 turn     Droid Electronics 

Cell Phone Detector 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 meters. 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 unauthorized video transmission. The circuit can detect both the incoming and outgoing calls, SMS and video transmission even if the mobile phone is kept in the silent mode. The moment the bug detects RF transmission signal from an activated mobile phone, it starts sounding a beep alarm and the LED blinks. The alarm continues until the signal transmission ceases. An ordinary RF detector using tuned LC circuits is not suitable for detecting signals in the GHz frequency band used in mobile phones. The transmission frequency of mobile phones ranges from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. ...

Fire Alarm The thermistor offers a low resistance at high temperature and high resistance at low temperature. This phenomenon is employed here for sensing the fire. The IC1 (NE555) is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The output(pin 3) of IC1 is couples to base of transistor T3(SL100), which drives the speaker to generate alarm sound. The frequency of NE555 depends on the values of resistances R5 and R6 and capacitance C2.When thermistor becomes hot, it gives a low-resistance path for the positive voltage to the base of transistor T1 through diode D1 and resistance R2. Capacitor C1 charges up to the positive supply voltage and increases the the time for which the alarm is ON. The larger the value of C1, the larger the positive bias applied to the base of transistor T1 (BC548). As the collector of T1 is coupled to the base of transistor T2, the transistor T2 provides a positive voltage to pin 4 (rese...

5 Km Long Range FM Transmitter Here we are presenting a long range FM transmitter that can cover a reasonable distance of 5 kilometers / 3 miles and beyond with a one watt RF power with full circuit details, bill of material and testing procedure. With 12 volt DC it will deliver 1 watt RF power. With Yagi antenna, looking like early days of TV antenna with aluminum pipes at both at transmitter and receiver end looking each other at line of sight distance, the range can be up to 5 km / 3 miles. This FM transmitter has 3 RF stages. A (VFO) Variable frequency Oscillator (30 mw) , A class C driver stage (150 mw) as buffer and A class C final RF power amplifier (1 Watt ) Basically every FM Transmitter has to have a Voltage Controlled Oscillator (VCO) . This is a high frequency oscillator whose output frequency changes based on the voltage applied at a particular control point. This is a variable frequency oscillator (VFO).Q1 with is associated components form the VF...

Active FM Antenna Booster This is a simple active antenna booster. This amplifier will pull in all distant FM stations clearly. The circuits is configured as a common-emmitter tuned RF preamplifier wired around VHF/UHF transistor Q1. Input coil L1 consists of four turns of 20SWG enamelled copper wire (slightly space wound) over 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration of transistor 2SC2570 is shown in the fm antenna booster schematic. Adjust input/output trimmers (VC1/VC2) for maximum gain. Active FM Amplifier Parts List: R1 = 27K R2 = 270 ohm R3 = 1K Tr1,Tr2 = 22pF, trimmer cap (15-40pF) C1,C2 = 5.6pF C3 = 0.001uF (1nF), ceramic C4,C5 = 0.01 (10nF), ceramic C6 = 0.1uF (100nF), ceramic Q1 = 2SC2498, 2SC2570, 2N5179, SK9139, or NTE10. NPN VHF/UHF transistor L1 = 4 turns of 20SWG magnet wire, 5mm diameter. (so-called 3T+1) L2 = 3 turns of 20SWG magnet...

Off Line-UPS Offers (100 -5000 Watts) With increased dependency on electric power for various domestic, commercial purposes and the seemingly declining capacity of power utilities in many countries, the need for additional backup power sources is on the rise. Various modules are already available to address these different needs. However, most modules are too expensive, too bulky, or too rigid in their power capacity, capability, and flexibility. The circuit described here is an off-line uninterruptible power supply. It has an expandable power stage design that can be easily modified for use with power ranges from as low as 100 W to as high as 5000 W with forced cooling. The design is based on the LM3524D, a popular industrial-grade, pulse-width-modulation (PWM) controller. This device is fully self-contained and has all of the necessary logic built-in to ensure a compact and cost-effective product. The controller offers: Complementary power drive output stage with 1...

500W 12V to 220V Inverter This is a 500W DC-to-AC inverter circuit diagram which produces an AC output at line frequency and voltage. 12VDC to 220V 50Hz inverter circuit will power 220V or 110V appliances from 12V car battery. The circuit is easy to make and is low cost. Use proper transformer. The output (in watts) is up to you by selecting different power rating transformer and power transistor rating. If you load electronic device which require 120V AC, then use transformer with 120V in output. Droid Electronics        

IR Proximity Sensor It is the same principle in ALL Infra-Red proximity sensors. The basic idea is to send infra red light through IR-LEDs, which is then reflected by any object in front of the sensor. Then all you have to do is to pick-up the reflected IR light. For detecting the reflected IR light, we are going to use a very original technique: we are going to use another IR-LED, to detect the IR light that was emitted from another led of the exact same type! This is an electrical property of Light Emitting Diodes (LEDs) which is the fact that a led Produce a voltage difference across its leads when it is subjected to light. As if it was a photo-cell, but with much lower output current.

Spy Bug FM Transmitter This tiny 88-108Mhz FM transmitter bug measures just 10mm x 17mm in size and as you can see in the photos the biggest components are just the microphone and the battery. You can use a small microphone from an older cell phones, they are small in size and have an excellent sensitivity. For an effective power supply the 9V battery (Duracell) is excellent and allows several hours of battery life, but if you want to have a smaller size it is better to use 2 or 3 lithium cells like the 2032 used in PCs. The circuit works well from 3 to 12V, the maximum range is obtained with 12V and a piece of 40-60cm cable as an antenna. It is possible to power transmitter by small LIPO battery (3.7-4V), in that case you must change R4 to 10K and R1 to 150ohm. The antenna length varies according to the output frequency, 300 / f then divides by 4 so as to have the antenna length in 1/4 wave length. 100Mhz = 75cm - 10% to compensate for losses make 68cm. For sim...

Junction Field Effect Transistor The Junction Field Effect Transistor, or JFET, is a voltage controlled three terminal unipolar semiconductor device available in N-channel and P-channel configurations In the  Bipolar Junction Transistor   tutorials, we saw that the output Collector current of the transistor is proportional to input current flowing into the Base terminal of the device, thereby making the bipolar transistor a “CURRENT” operated device (Beta model) as a smaller current can be used to switch a larger load current. The  Field Effect Transistor , or simply  FET however, uses the voltage that is applied to their input terminal, called the  Gate  to control the current flowing through them resulting in the output current being proportional to the input voltage. As their operation relies on an electric field (hence the name field effect) generated by the input  Gate  voltage, this then makes the  Field Effect ...