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Saturday, November 8, 2014

Build a Radio Wave Alarm

This simple circuit is sure to have the police beating a path to your door- however, it has the added advantage of alerting you to their presence even before their footsteps fall on the doormat.Simple Radio Wave Alarm Circuit Diagram :

Notes :

The circuit transmits on Medium Wave (this is the small problem with the police). IC1a, together with a sensor (try a 20cm x 20cm sheet of tin foil) oscillates at just over 1MHz. This is modulated by an audio frequency (a continuous beep) produced by IC1b. When a hand or a foot approaches the sensor, the frequency of the transmitter (IC1a) drops appreciably.
Suppose now that the circuit transmits at 1MHz. Suppose also that your radio is tuned to a frequency just below this. The 1MHz transmission will therefore not be heard by the radio. But bring a hand or a foot near to the sensor, and the transmitters frequency will drop, and a beep will be heard from the radio.
Attach the antenna to a multiplug adapter that is plugged into the mains, and you will find that the Medium Wave transmission radiates from every wire in your house. Now place a suitably tuned Medium Wave radio near some wires or a plug point in your house, and an early-warning system is set up.
Instead of using the sheet of tin foil as the sensor, you could use a doorknob, or burglar bars. Or you could use a pushbutton and series resistor (wired in series with the 33K resistor - the pushbutton would short it out) to decrease the frequency of IC1a, so activating the system by means of a pushbutton switch. In this case, the radio would be tuned to a frequency just below that of the transmitter.

Monday, September 1, 2014

Measuring Milliohms with a Multimeter

Low values of resistance can be troublesome especially when large current s f low through them. A current of, say, 10 A passing through a terminal with a contact resistance of 50 m? will produce a voltage difference of 0.5 V. This resulting power loss of five watts is dissipated in the termination and can give rise to a dangerously high temperature which may degrade insulation around the wires.
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Circuit diagram :

Measuring Milliohms with a Multimeter Circuit Diagram
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Measuring low values of resistance is not easy. Low cost multimeters do not include a milliohm measurement range and specialist equipment is expensive. The simple schema described here allows milliohm measurements to be made safely on a standard ist equipment is expensive. The simple schema described here allows milliohm measurements to be made safely on a standard multimeter. The schema consists of little more than a 6 V voltage regulator and a mains adapter capable of supplying around 300 mA at 9 to 12 V.

The schema supplies a fixed cur-rent output of 100 mA or 10 mA selected by switch S1. This connects either the 60 ? or 600 ? resistor into the constant current generator schema. The resistor values are produced by paralleling two identical resistors; 120 ? and 1.2 k? from the E12 standard resistor range. Two test leads with probes are used to deliver current to the test resistance. The resultant voltage drop is measured by the multimeter (M1). With the test current set to100 mA a measurement of 1 mV indicates a resistance of 10 m?. At 10 mA (with S1 in the position shown in the diagram) a measurement of 1 mV indicates a resistance of 100 m? while 0.1 mV is equal to 1 m?. Diode D1 protects the meter from too high an input voltage.

With the voltmeter connected as shown in the diagram it measures not only the voltage drop across RX but also that produced by the resistance of the test leads, and probes. To make a true measurement, first touch the probes close together on the same lead of the test resistance and note the reading, now place the probes across the test resistance and note the reading again. The first reading measures just the test leads and probes while the second includes the resistance RX. Subtract the first measurement from the second to get the value of RX.

The accuracy of the measurements are influenced by the contact resistance of switch S1, the precision of resistors R1 to R4, the 6 V supply level and of course the accuracy of the measuring voltmeter. For optimum decoupling C1 should be fitted as close as possible to pin1 of IC1. An additional electrolytic capacitor of around 500 µF can be used at the input to the schema if the input voltage from the AC power adapter exhibits excessive ripple.

Author : Klaus Bertholdt - Copyright : Elektor

Sunday, August 31, 2014

Build a Isolated 15V To 2500V Power Supply Wiring diagram Schematic

Build a Isolated 15V To 2500V Power Supply Circuit Diagram. A dc-dc converter using a 74HC04 drives Tl. Tl is a ferrite-core transformer using a Fair-Rite, Inc. P/N 5975000201 (uo + 5000) and has a 7-turn primary and a 25-turn secondary. Kynar, #30 wirewrap wire is used. With Tl, the schema isolation is good to 2500 V.

Isolated 15V To 2500V Power Supply Circuit Diagram

Monday, August 25, 2014

Build a Cuckoo Sound Generator Circuit Schematic

This schema generates a two-tone effect very much alike the cuckoo song. It can be used for door-bells or other purposes thanks to a built-in audio amplifier and loudspeaker. Used as a sound effect generator it can be connected to external amplifiers, tape recorders etc. In this case, the built-in audio amplifier and loudspeaker may be omitted and the output taken across C8 and ground. There are two options: free running, when SW1 is left open, and one-shot, when SW1 is closed. In this case a two-tone cuckoo song will be generated at each P1 pressing.

Cuckoo Sound Generator Circuit diagram:

Parts:

R1,R5___________1K 1/4W Resistors
R2_____________50K 1/2W Trimmer Cermet
R3______________8K2 1/4W Resistor
R4_____________82K 1/4W Resistor
R6______________1M 1/4W Resistor
R7,R17,R20,R21_22K 1/4W Resistors
R8,R10,R11,R19_10K 1/4W Resistors
R9____________150K 1/4W Resistor
R12_____________4K7 1/4W Resistor
R13___________100K 1/4W Resistor
R14___________220R 1/4W Resistor
R15,R22________20K 1/2W Trimmers Cermet
R16____________10R 1/4W Resistor
R18___________200K 1/2W Trimmer Cermet
C1,C11_________47nF 63V Polyester or Ceramic Capacitors
C2,C10,C12____220µF 25V Electrolytic Capacitors
C3____________220nF 63V Polyester or Ceramic Capacitor
C4_____________22nF 63V Polyester or Ceramic Capacitor
C5,C6,C8,C9___100nF 63V Polyester or Ceramic Capacitors
C7,C13,C14_____10µF 63V Electrolytic Capacitors
D1,D2,D3,D6__1N4148 75V 150mA Diodes
D4,D5_________BAT46 100V 150mA Schottky-barrier Diodes
Q1,Q2_________BC547 45V 100mA NPN Transistors
IC1____________7555 or TS555CN CMos Timer IC
IC2____________4093 Quad 2 input Schmitt NAND Gate IC
IC3____________4017 Decade counter with 10 decoded outputs IC
IC4___________LM386 Audio power amplifier IC
P1_____________SPST Pushbutton
SW1____________SPST Switch
SPKR___________8 Ohm Loudspeaker

Circuit Dis....
IC1 is wired as a square wave generator and produces both tones of the cuckoo song. The frequency of the higher one (667Hz) is set by means of Trimmer R2. When IC2D output goes low, a further Trimmer (R22) is added to IC1 timing components via D6, and the lower tone (545Hz) is generated. To imitate closely the cuckoo song, the square wave output of IC1 is converted to a quasi-sinusoidal wave form by R3, R4, C3 and C4, then mixed with the white noise generated by Q1, R6.

Q2 has two purposes: it mixes the two incoming signals and gates the resulting tone, shaping its attack and decay behavior by means of the parts wired around its Emitter. IC4 is the audio power amplifier driving the speaker and R15 is the volume control. The various sound and pause timings for the schema are provided by the clock generator IC2A driving the decade counter IC3. Some output pins of this IC are gated by IC2C, IC2D and related components to drive appropriately the sound generator and the sound gate.

When SW1 is left open the schema operates in the free-running mode and the cuckoo song is generated continuously. When SW1 is closed, the schema generates two tones then stops, because a high state appears at the last output pin (#11) of the decade counter IC: therefore the count is inhibited by means of D1 feeding pin #13. The schema is reset by a positive pulse at pin #15 of IC3 when P1 is pressed.

Setup:

Best results will be obtained if the two tones frequencies are set precisely, i.e. 667Hz for the first tone and 545Hz for the second: in musical terms this interval is called a Minor Third. Obviously a digital frequency counter, if available, would be the best tool to setup R2 and R22, but you can use a musical instrument, e.g. a piano or guitar, tuning-up the notes accurately by ear.

Disconnect temporarily R22 from D6 anode.
Connect the digital frequency counter to pin 3 of IC1.
Adjust R2 in order to read 667Hz on the display.
Connect R22 to negative ground and adjust it to read 545Hz on the display.
Restore R22 - D6 connection.

Tuning by ear:

Disconnect temporarily R22 from D6 anode.
Disconnect C8 from Q2 Collector and connect it to R4, C4 and C5 junction.
Adjust R2 in order that the tone generated by the loudspeaker is at the same pitch of the reference note generated by your musical instrument. This reference note will be the E written on the stave in the fourth space when using the treble clef.
Connect R22 to negative ground and adjust it in order that the tone generated by the loudspeaker is at the same pitch of the reference note generated by your musical instrument. This second reference note will be the C-sharp written on the stave in the third space when using the treble clef.
Restore R22 - D6 and C8 to Q2 Collector connections.

Notes:

The master clock can be adjusted by means of R18.
The percentage of hiss and sound in the mixing schema, setting the tone character, can be varied changing R8 and R7 values respectively.
Any kind of dc voltage supply in the 12 - 15V range can be used, but please note that supply voltages below 12V will prevent operation of the white noise generator.
An amusing application of this schema is to use a photo-resistor in place of P1, then placing the unit near the flashing lamps of your Christmas tree. A sweet cuckoo song will be heard each time the lamp chosen will illuminate.

Source: Red Free Circuit Design

Saturday, August 23, 2014

Build a Solar Garden Light Wiring diagram Schematic

This is a Solar Garden Light Circuit Diagram that consists of a very simple system garden lighting that can be done by using some common electronic parts and a small solar panel. The electronic design is simple yet very efficient, has the advantage of being solar powered, it requires only one transistor, one 2.5 volt solar panel and some other common electronic components you can remove junk.

This solar lighting system automatically turns on the LEDs when the solar panel detects no light turns off when the solar panel produces more than 1v and charges the battery when the panel produces more than 2.1V

The coils in this schema require a core material F29 and they must be made with wire of 0.095 mm in core 2.6x6mm. "This schema uses the system joule thief (joule thief) to provide voltage necessary for the LED, so other coils can be tested.

Solar Garden Light Circuit Diagram

Monday, August 18, 2014

Build a Instrumentation Amplifier Wiring diagram Schematic

How Build a Instrumentation Amplifier . Three-amplifier schema consumes only 135 /tW of power from a Â±1 V power supply. With a gain of 101, the instrumentation amplifier is ideal in sensor interface and biomedical preamplifier applications . The first stage provides all of the gain while the second stage is used to. provide common mode rejection and double-ended to single-ended conversion .

Build a Instrumentation Amplifier Circuit Diagram

Thursday, August 14, 2014

First LED lamp that replaces a 100 watt incandescent

Already reached the market the first LED lamp that replaces 100 watt incandescent bulb, this was the announcement of Osram Sylvania. She becomes the first to do is replace the new lamp will join the existing line of Ultra LED 40, 60 and 75 watt (equivalent to incandescent powers), it consumes 20 watts and have a lifespan of 25,000 hours about 25 times more than incandescent bulbs.It has a CRI of 80, an illumination of 1,600 lumens and a warm white color temperature of 2700k. It also is adjustable and, of course, free of mercury and lead.

First LED lamp that replaces a 100 watt incandescent

Wednesday, August 13, 2014

How to Match a Car Subwoofer and Amplifier

Need help knowing how to match a car subwoofer and amplifier? Tired of your friends constantly asking you to pair a sub and amp for them? Watch this video (or send it to a friend) and learn about the three major points of matching subwoofers and amps:

The Total RMS of the System

The Final Impedance of the System

Types of Amplifiers

In this video we use the 750 watts RMS Kicker CVX (CompVX) subwoofer and the Kicker ZX750.1 amplifier (750 watts RMS @ 2 ohm) as an example of a perfectly matched subwoofer and amp.