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Measuring and Test Circuit

Index 7

SENSITIVE GEOMAGNETIC DETECTOR

Published:2013/5/7 21:14:00 Author:muriel | Keyword: SENSITIVE GEOMAGNETIC DETECTOR

SENSITIVE GEOMAGNETIC DETECTOR
This is a rather sensitive circuit which will detect minute variations of a magnetic field, particularly the Earth magnetic field. The principle is based on an audio beat tone generated by two identical oscillators. These must be built in the same manner with the same type of components. In this way we minimize influence from temperature and voltage variations. The two oscillators, called probes, are housed in plastic boxes padded, on the inside, with copper wires terminated in one point only and running parallel to the ferrite rod. This rod, together with the coil was removed from an old Medium Wave radio and a small and powerful magnet was glued on one side. An extra magnet was placed on the outside of one of the boxes in order to set the initial or zero beat tone. This magnet is rotated or moved up and down until you hear the right frequency. A small hole is made in each plastic box in order to adjust the trimmer capacitor. Switch S1 will enable the sub-Hertz detector: in this way you will be able to hear the beat note even if the difference between the two probes is below the threshold level of around 20Hz and you will pick up differences well below 1Hz. The two probes are connected to the main box using standard RG58 coaxial cable tested up to a length of 15m. Operating frequency is 1.25MHz and it is sensitive enough to feel the rotation of a speaker magnet 2m away. Battery voltage is 9V. (View)

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LED Audio VU Meter

Published:2013/4/26 1:37:00 Author:muriel | Keyword: LED , Audio , VU Meter

LED Audio VU Meter
(View)

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Stereo VU Meter

Published:2013/4/26 1:36:00 Author:muriel | Keyword: Stereo VU Meter

Stereo VU Meter
This is a STEREO LED LEVEL METER. It’s the cheapest and best bar graph display available and best of all, it uses readily available components.You only need a handful of LEDs, 22 transistors, some resistors, diodes and a set of electros – it doesn’t require any chips. (View)

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Voltage and Current Limited Audible Continuity Tester circuit

Published:2013/3/29 4:31:00 Author:Ecco | Keyword: Voltage and Current, Limited Audible, Continuity Tester

Voltage and Current Limited Audible Continuity Tester circuit
Using this continuity tester circuit, a failure of PCB tracks be examined without looking directly at the tracks routing, which is can be very frustrating. The indication of this circuit is done by an audible alarm (a buzzer). This circuit can be used to indicate continuity below any resistance value up to 35 ohms by adjusting the circuit. To make sure this circuit doesn’t damage any installed parts on the board, the voltage and current of this circuit is limited. Here is the schematic diagram of the circuit: (View)

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True Stereo Indicator Detecting L-R Signal Difference circuit

Published:2013/3/28 4:07:00 Author:Ecco | Keyword: True Stereo Indicator, L-R Signal Difference

True Stereo Indicator Detecting L-R Signal Difference circuit
This true stereo indicator is different from what we usually find on FM radio receiver, which is usually a pilot tone detector. A stereo broadcast from FM radio station contain pilot tone, but a presence of pilot tone doesn’t necessarily a stereo broadcast signal since a mono FM transmitter ca broadcast pilot tone as well. Since this circuit detect the difference between left and right channel, this circuit can detect a real stereophonic programs. When there is no difference between R and L input signals, the output A1 and output A2 is at the same potential. That will make a a virtual ground rail at half the supply voltage. Here is the schematic diagram of the circuit: (View)

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ZENER DIODE TESTER Circuit

Published:2013/3/5 21:05:00 Author:Ecco | Keyword: ZENER DIODE, TESTER

ZENER DIODE TESTER Circuit
This circuit will test zener diodes up to 56v. See Talking Electronics website, left index, 200 Transistor Circuits (circuits 1-100) and go to Zener Diode (making) to see how to make a zener diode and how to create a zener voltage from a combination of zeners. Place the zener across the terminals in the circuit below and read the value across it with a multimeter set to 50v range. (View)

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Non-contact AC measuring circuit

Published:2013/3/5 0:45:00 Author:Ecco | Keyword: Non-contact, AC, measuring circuit

Non-contact AC measuring circuit is shown as figrue. (View)

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Photosensitive element test circuit

Published:2013/3/4 3:12:00 Author:Ecco | Keyword: Photosensitive element, test circuit

Photosensitive element test circuit is shown as figure. (View)

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DARK DETECTOR Circuit

Published:2013/3/4 21:36:00 Author:Ecco | Keyword: DARK DETECTOR

DARK DETECTOR Circuit
When the level of light on the photo-cell decreases, the 555 is activated. Photo-cells (Photo-resistors) have a wide range of specifications. Some cells go down to 100R in full sunlight while others only go down to 1k. Some have a HIGH resistance of between 1M and others are 10M in total darkness. For this circuit, the LOW resistance (the resistance in sunlight) is the critical value.More accurately, the value for a particular level of illumination, is the critical factor. The sensitivity pot adjusts the level at which the circuit turns on and allows almost any type of photo-cell to be used. (View)

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CONTINUITY TESTER Circuit

Published:2013/3/4 21:35:00 Author:Ecco | Keyword: CONTINUITY TESTER

CONTINUITY TESTER Circuit
This circuit will detect low resistances and high resistances to produce a tone from the speaker. It will detect up to 200k and the circuit automatically turns off when the probes are not used. (View)