Electronic schematics, circuit designs
Mobile phone sniffer - gsm telephone detector
With this mobile phone sniffer will track down mobile phones. Use this handy directional finder in situations and locations where the use of a mobile phone is forbidden. This neat unit will not only detect the presence of mobile phone activity (voice or text), it can home in on the culprit!
Apart from mobile phones this unit can also pick-up the signals sent out by modern digital cordless (DECT) phones. These operate around the same frequency as cell phones. As with cell phones you will not be able to eavesdrop on conversations because the speech is digitally encoded but you will be able to hear the telltale RF pulses.
Microwave ovens operate in the SHF band at about 2,400 MHz and you can use this unit to check for RF leaks around the door seal. Adding a few turns to the two coils and increasing the antennas length will allow you to experiment at lower frequencies in the short wave radio spectrum (not in stereo however).
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Preamplifier scanner
This circuit scan all the preamplifier entries to identify where is a audio signal and that entry remains selected. After a sign of signal absence, scanning resumes. Scanning action is supported by rectangular signal generator IC2c. Scanner’s entries are connected to the audio entries from volume control board of the preamplifier.
Useful signal is amplified by 40 times with IC1c and IC1d, then summator amplifier IC1a combine left and right signals. As soon as a signal of music or vocal appears on entry lines, C1 partialy discharges, very quickly. As long as it receives the input signal, a part of the capacitor C1 load is
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CGA / SCART adapter
CGA adapter / SCART has great advantages as it does not require separate power source and that uses very few external components, which can be easily adapted in the SCART connector. The signals from R, G and B pins of the CGA’s board are converted from TTL levels to SCART levels with resistors R4, R5 and R6 and entry’s impedance (75 Ω) of scart inputs.
Output Impedance of voltage dividers thus created is not exactly 75 Ω as specified for SCART inputs, but in practice the behavior seems to result not big differences.
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