indicator circuits
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Low Battery Indicator
Dec 19th
It is an ideal solution to protect rechargeable batteries from deep discharge. It gives an LED indication when the voltage level in the battery drops below 5.1 volt. CA 3140 Op Amp is used as a comparator with a zener to fix voltage in its non inverting input. Preset VR1 set the voltage level just below 5.1 volt at the inverting input. When the battery voltage is above 5.1 volt, zener provides regulated 5.1 volt to pin3 of IC and its output goes high to light LED. It indicates that battery is full. If the voltage in the battery drops More >
Polarity indicator
Dec 12th
Is is easy to test the polarity of a circuit’s point whether it is positive or negative by using the tester circuit featured here. The tester circuit has a high input impedance (around 1 megaohms) to avoid loading the point being tested. In testing sensitive points however, (inputs of opamps), the input impedance must be taken into consideration. (more…)
Radio field indicator with MOS-FET
Nov 22nd
A rf field indicator is required to verify power stages and transmitters antennas. With this radio field indicator you can measure radiated energy from antenna. This circuit is very sensitive, a weak signal is enough. The S2 commutator allows to select : 480KHz … 2.4MHz / 2.4MHz … 12MHz / 12MHz … 40MHz. A 30cm long wire is enough as a antenna. (more…)
UHF indicator – wavemeter
Oct 11th
UHF indicator or wavemeter is some kind of device that measures frequencies and determines LC circuit frequecy resonance . This device does not need to radiate. The oscillator is build with T1 and T2 (2 x BF494) and can be adjusted with C1 and Lx. The Lx coil is connected outsite of the metal box and has to be changeble handiest. If Lx is inductively coupled with another LC coil wich has the same frequency as the wavemeter, then will extract energy from oscillator coil, this will result in a voltage reduction. (more…)
Radio field signal strength indicator
Oct 4th
A radio field signal strength indicator is very usefull for determine radiation patterns of transmitters antennas. An ancillary antenna must be put close to main transmitter antenna. The received signal is applied to L1,L2 and C2, this allows the field indicator circuit to adjust to the same frequency as the transmitter. With the coils values from the radio signal indicator wiring schematic, the frequency band is 6 to 60MHz. A pair of headphones can be connected to hear the transmission. The total impendance of the headphones has to be at least 2.2Kohm. (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…)
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