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Circuit Description

This applet demonstrates the set-reset flipflop. The normally-open-type contact (interruptor) used in the previous applet has been replaced by a second relay.

Click the input switches or type the 's' and 'r' bindkeys to control the circuit and watch the resulting behavior.

As in the previous (one-relay) flipflop, the basic idea behind the circuit is the parallel-connection of the 'set' switch and one switch of the 'master' relay. Once the 'master' relay has been activated by a (strong) high voltage on the 'set' input via its A-A0 contact, the relay keeps feeding itself via the (now switched) A-A1 connection.

When the second relay is activated by a (strong) high voltage on the 'reset' input, the opened connection of the second relay interrupts the current through the 'master' relay coil, and the master relay is deactivated.

Additionally, the second switch of the relay has been conntected to both the supply voltage (port B1) and ground (port B0). Therefore, the Q output of the flipflop is driven strongly to both high and low levels.

Again, the resulting truth table is as follows:

  SET  RESET  |  Q    Q*
--------------+-------------------
    0      0  |  *    Q   (store)
    0      1  |  *    0   (reset)
    1      0  |  *    1   (set)
    1      1  |  *    0   (reset)