Circuit improves on first-event detection

摘要

The circuits in figures 1 and 2 exhibit certain advantages over the circuit shown in the Design Idea in EDN, "Circuit detects first event," May 3, 2001, pg 89. The n-player first-event-detection circuit offers several improvements: 1. It has fewer passive components. It needs only n diodes instead of (n~2+n)/2 for three or more players. And, excluding the LEDs' current-limiting resistors, the circuit needs only n+1 resistors instead of 5n. 2. The circuit uses less expensive ICs. The 74F74 or 4013 costs only 25% of the price of a LMC6762 (DigiKey catalog). 3. The circuit offers inexpensive and simple scalability. You can easily add any number of additional player-event-detection channels to an event-detection configuration. All that's needed is that you connect the additional circuits to a common five-wire bus consisting of V_(CC), ground, the Reset, the SwitchBus signal, and the CaptureInhibit signal. Thus, the wiring complexity is independent of n; in other words, it is O(1). Expanding the number of players for the original event-detection circuit requires additional diode-connected reset signals from each channel to all other channels, resulting in a wiring complexity that scales as (n~2-2n), or O(n~2).