Autodisconnection for audio equipment
This simple circuit disconnects equipment rack of your audio in case has not delivered a sound a specified period. Circuit is operated by pressing his S1, which produces loading of C1. Further, switch IC1b AO exit in the state “up” and the audio equipment is powered from the network through semiconductor relay ISO1.
LINE OUT terminal signal of power audio amplifier is applied to the entry circuit through connector K1. Operational amplifier IC1a is configured to function as a signal detector with release threshold of approximately 50mV. Observe that potential for audio amplifier ground is high in the autodeconnecting circuit at approximately +4.5 V, through R1-R2-R3 resistors. When the audio signal is greater than 50 mV, IC1output goes in H state and T1 transistor starts to conduct. In the absence of audio signal input C1 is
Read the rest of this entry »
Neon tubes brightness adjustement
The brightness of a neon tube can not adjust as easily as that of a bulb with Incandescent tube because it starts only when a voltage much higher than that of the network, then remains on at electrical network voltage.
Normally, the high starting voltage is obtained by the interruption of current which circulates through a choke coil. This is usually a starter to ensure a sufficiently large current through the tube filaments.
These starter functions are taken over by circuit presented which also allows adjustment of the neon brightness.
When we switch on the neon tube, the brightness control potentiometer, P1, should be placed on the position of maximum brightness of the tube, to facilitate the start.
Read the rest of this entry »
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).
Read the rest of this entry »
