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Wiring your first physical breadboard is a frustrating experience. One wrong connection and the circuit does not work. Unfortunately without an experienced instructor by your side, it is difficult to find out where is the mistake. Our breadboard simulator acts as a virtual and patient instructor checking on your every connection.

Practice does not make perfect. Only perfect practice makes perfect - Vince Lombardi

Use the following steps to complete the wiring of the breadboard

  • Select your schematic. The 1 to 2 demultiplexer is the easiest to start. When you select your schematic, the ones where you have completed the breadboard will be shown with a green background.
  • Operate the switches in the circuit simulator. Read the description of the circuit for more 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.
  • 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.
  • Sign in with your Google account to save your breadboard connections and earn a digital badge.
  • Note that all the VCC (red wire) and GND (black wire) connections are already done. When you wire up the actual circuit using the under US$10 Home Laboratory Kit, do remember to connect the VCC and GND wires.
  • Click Help on menu to hide/show this Help panel. This site is optimised for computer browsers.

Note that the holes connected by the blue lines are electrically connected in the breadboard.

breadboard internal connections

If you are unfamiliar with the breadboard, there are many resources available online that explains how they work. We recommend this quick Breadboard Infographic from Make Breadboarding Workshop or the longer Breadboard Tutorial from Science Buddies.

SR NOR latch

When using static gates as building blocks, the most fundamental latch is the simple SR latch, where S and R stand for set and reset. It can be constructed from a pair of cross-coupled NOR logic gates. The stored bit is present on the output marked Q.

While the S and R inputs are both low, feedback maintains the Q and Q outputs in a constant state, with Q the complement of Q. If S (Set) is pulsed high while R (Reset) is held low, then the Q output is forced high, and stays high when S returns to low; similarly, if R is pulsed high while S is held low, then the Q output is forced low, and stays low when R returns to low.

The R = S = 1 combination is called a restricted combination or a forbidden state because, as both NOR gates then output 0s, it breaks the logical equation Q = not Q. The combination is also inappropriate in circuits where both inputs may go low simultaneously (i.e. a transition from restricted to keep). The output would lock at either 1 or 0 depending on the propagation time relations between the gates (a race condition). In certain implementations, it could also lead to longer ringings (damped oscillations) before the output settles, and thereby result in undetermined values

    Notes:
  • Q0 is the previous state of Q and Q0 is the previous state of Q.
  • R and S are asynchronous inputs - that is the output responds to these input immediately. They are active high inputs. Click on their respective (SW7 and SW6) switches and observe.
  • S sets the output to 1 and R resets the output to 0.
  • Both R and S cannot be high at the same time - the output is undefined.

7402 NOR Gate IC Pin Out

7402 NOR Gate IC