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Circuit improves further on first-event detector

-June 27, 2002

The circuits in Figure 1 have certain advantages over those in a previous Design Idea (Reference 1). The first-event detector with autoreset (Figure 1a) consists of N sets of monostable multivibrators, using 4001 logic circuits with LEDs attached. After any player (1 through N) presses a pushbutton, the corresponding monostable multivibrator switches on, and its associated LED lights. The voltage at Point A changes to a level of nearly 2V (the forward voltage of the LED). After that instant, no other player can change the situation by pressing a pushbutton, because, to switch, the monostable multivibrators need a voltage exceeding 4V. After an interval of 0.5RC (nearly 15 sec for R=1 MΩ and C=33 µF), the monostable multivibrator returns to its previous state, and the circuit is ready for its next first-event detection. Figure 1b shows another first-event detector with autoreset, using 4011 logic ICs. This circuit is a mirror image of the circuit in Figure 1a and operates similarly.

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Reference
  1. Arendt, Lawrence, "Circuit improves on first-event detection," EDN, Aug 16, 2001, pg 106.

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