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Circuit Detects Current Pulses: 01/06/94 EDN-Design Ideas / (Electronic Circuit diagram added 03/03) The pulse
detector provides a visible indication of positive and negative current pulses. The pulses amplitudes can vary from20 to150 mA. The pulses durations can range from10 to40 msec, and their
repetition rate can span40 to180 pulses/minute.
Crystal Radio #1: This is a generic circuit, the first true radio receiver in history. Description: Crystal radio
requires no power supply to operate because it uses energy from the signals it receives. Performance is - like one should expect - poor. Nevertheless, with a good antenna and proper ground, it
shouldn't be too difficult to tune to a strong AM station. While this circuit is very simple, many points should be observed. The variable capacitor is relatively hard to get in a store
these days, so your best bet to find one could be a junked AM receiver. Connect the case to the antenna and the central rod to ground. Otherwise, you'll de-tune the circuit every time you
touch the capacitor.…. (added 10/05)
Crystal Radio #2: RF Receivers & Receiver Circuits Crystal Radio (Electronic circuit added 5/02)
Crystal radio with Amplifier: An improved crystal radio with a two-stage audio amplifier. The 2N3904 (or any other
general-purpose NPN) acts as a preamplifier while the LM386 boosts the signal high enough to drive low impedance Walkman headphones or perhaps even a small speaker. (added 10/05)
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