I'm having some trouble with my circuit based on the design below, that I built for the lab. I'm using a Schmitt trigger clock. I built the circuit on a breadboard and connected it to the clock and button inputs as specified in the lab instructions. I also added the necessary components for the Schmitt trigger clock, including a capacitor and resistor.

When I press the b button, q1+ turns on and stays on as long as I keep the button pressed. However, when I let go, it turns off and doesn't turn back on when I press the clock. Also, when I press the b and a buttons at the same time, q0+ turns on, but nothing happens when I let go off the buttons and then press the clock. I was wondering if you could help me out with this. I've checked the connections and they all seem to be correct, so I'm not sure what the issue is. I suspect it might have something to do with the Schmitt trigger clock or the way I've set up the circuit, but I'm not sure.

The goal is to create a working finite state machine (FSM) based on the state diagram corresponding to the student's date of birth. The FSM should be able to switch between different states in response to input from buttons. The lab also involves using a Schmitt trigger clock to generate clean clock signals for testing the circuits.

Thanks in advance!

Lab instructions and picture of my breadboard enter image description here enter image description here enter image description here

  • \$\begingroup\$ Are you pressing the clock after releasing the button? The positive edge of the clock should trigger the read of the D Flip-flop. For example, when q1+ is high as you hold b, switch the clock. This should set q1 high. If you let go of b beforehand, q1+ is low, and so you set q1 low. \$\endgroup\$ Dec 14, 2022 at 5:24
  • \$\begingroup\$ Okay, so when I pressed b and as I hold b and pressed clock now q1 was set high and the LED is still on. On Logisim, if b is on and I press on the clock, the LED should turn off, but it doesn't... cdn.discordapp.com/attachments/1050887601042759710/… \$\endgroup\$ Dec 14, 2022 at 5:49
  • \$\begingroup\$ @imthegman55 ... \$\endgroup\$ Dec 14, 2022 at 5:49
  • \$\begingroup\$ And here is what it looks like once I turn off the clock and turn off the clock on Logisim. cdn.discordapp.com/attachments/1050887601042759710/… On my breadboard, pressing the clock does nothing to turn q1+ LED off once it's turned on. It would only reset if I push on b and a simultaneously, and at the same time, press clock once. Then q1+ would turn off. \$\endgroup\$ Dec 14, 2022 at 5:52

1 Answer 1


You should test your Karnaugh map.
For doing it, create two new buttons which will drive the reset and preset accordingly of the D-FF.
Then set the Q1 and Q0 as you want, and check your K-map line by line.
I did so, and I checked that your last line (for Q1Q0=(1,0) is "wrong" ...
Will recheck mine also.

enter image description here


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