Hello! I have a problem with my circuit that I translated from Multisim to pcb, in Multisim my counter works perfectly (BCD starts at 0000), my main problem is in the PCB, my BCD counter starting at an undefined state, sometimes 1111, sometimes 0110, my switch is connected directly to a 5V voltage regulator directly to the power supply (the GROUNDIN and VOLTAGEIN ports), what could be causing this BCD to not start at 0?

I was thinking of putting the toggle switch on a different location and maybe it will fix this problem....? I'm not so sure

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There is no guarantee what state it will start up in.
If you want it to start up at 0, then you must implement a power-on reset circuit.

 

There is no guarantee what state it will start up in.
If you want it to start up at 0, then you must implement a power-on reset circuit.

Which pin in the 74LS90 can I use for that? There are 2 reset pins in the 74LS90 if I'm correct

 

Hi skr,
Do you have a circuit diagram that you could post?
E

 

Which pin in the 74LS90 can I use for that? There are 2 reset pins in the 74LS90 if I'm correct

Either of the R0 pins
[Correction] BOTH the R0 pins.
A TTL IC with positive-going resets? Whatever next?

 

Hi skr,
Do you have a circuit diagram that you could post?
E

yes, this was the circuit before I converted this into PCB

 

Hi sk,
Modify.
E

 

Use a capacitor/resistor to trigger the POR for R0/1 and R0/2, similar to this:
https://electronics.stackexchange.c...acitor-and-resistor-in-power-on-reset-circuit