I am making a control system as my project. Here i have used 2 555 timers one in monostable and the other sin astable. The monostable outputs when process one button is pushed and this also triggers the astable 555 timer. The 7 seg attched to the monostable 555 which is the left one shows how many times the process is initiated and the 7seg with astable 555 shows time taken for the process. Now when i start the monostable 555 the astable 555 starts but it counts from 1 not 0. And also i would like to add that when the process 1 button is pressed again the 7 seg attached to the astable 555 resets and starts from 0 again.

enter image description here Image of circuit before simulation.

enter image description here Image of circuit after simulation. As can be seen it is starting from 1.


1 Answer 1


It's worse than the simulation- those counters will start at more-or-less random numbers at power up. Also you must not leave the reset inputs floating.

Connect the MR inputs (pin 15) to an active-high reset signal to reset the counters to zero.

  • \$\begingroup\$ Any advice on how i can make sure that the 7 seg does not start with random number. Basically i want it to start with 0 and up. \$\endgroup\$ Dec 15, 2014 at 14:37
  • \$\begingroup\$ Connect the reset inputs (pin 15) to a signal that is high for a time after power is applied and stable. You can use another 555 but a proper reset circuit such as an ADM810 will be much more reliable if the power is not switched on and off cleanly each and every time. \$\endgroup\$ Dec 15, 2014 at 14:51
  • \$\begingroup\$ Thanks for replying. And also i would like to ask if there is any switch that detects voltage or current and switches to say state 1 and when there is no current or voltage switches to state 2. Basically what i am saying is that there is something like a rotatory switch that switches automatically by detecting voltage or current. \$\endgroup\$ Dec 15, 2014 at 15:16
  • \$\begingroup\$ Also we are not allowed to use micro controllers. \$\endgroup\$ Dec 15, 2014 at 15:18
  • \$\begingroup\$ AD810 as I suggested detects voltage. \$\endgroup\$ Dec 15, 2014 at 15:20

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