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Use the following steps to complete the wiring of the breadboard

  • Select your circuit. If this is your first time, choose the SR NAND or SR NOR.
  • Operate the switches in the circuit simulator. Read the description of the circuit if you need additional information.
  • Using the schematic, wire up the circuit in the breadboard simulator. When a wire end is placed in a socket of the breadboard that corresponds to a node on the schematic, the respective node of the schematic will turn red.
  • If a correct connection is made, the wire ends will snap into the socket.
  • Note that all the VCC (red wire) and GND (black wire) connections are already done.
  • When all the nodes are wired up, a red LED will light up near the VCC/GND terminals.
  • You may now operate the breadboard switches and observe the LED results.
  • When you wire up the circuit using a real digital trainer, do remember to wire the VCC and GND wires and power up the digital trainer.
  • You must login using your facebook account to save or restore the breadboard connections.
  • Click to close any of the panes (breadboard/schematic/description/help) and click on the corresponding menu item to open it.

If you are unfamiliar with the breadboard, there are many resources available online that explains how to they work.

Johnson Counter

A Johnson counter is a modified ring counter, where the inverted output from the last flip flop is connected to the input to the first. The register cycles through a sequence of bit-patterns. The MOD of the Johnson counter is 2n if n flip-flops are used. The main advantage of the Johnson counter counter is that it only needs half the number of flip-flops compared to the standard ring counter for the same MOD.

This circuit is implemented using D-type flip-flops.

    Notes:
  • Enable the flips flops by clicking on the RESET switch (SW6).
  • Click on CLK (SW7) switch and observe the changes in the outputs of the flip flops. SW7 is a momentary switch.
  • The D flip flop clock has a rising edge CLK input. For example Q1 behaves as follows:
    • The D input value just before the CLK rising edge is noted (Q0).
    • When CLK rising edge occurs, Q1 is assigned the previously noted D value (Q0).
  • The MOD or number of unique states of this 3 flip flop johnson counter is 6.