Hi guys,

I'm trying to prototype a 7 segments display counter with 555 timer circuit using multisim and the circuit works but it counts in multiples of 2 and I have no idea why. Any chance you guys can take a look and help me figure out why?

 

My guess is that you have INA (pin 14) connected to QA (pin 12). The LS90 will count on INA and/or INB so I think its picking up QA as an additional clock edge.

 

My guess is that you have INA (pin 14) connected to QA (pin 12). The LS90 will count on INA and/or INB so I think its picking up QA as an additional clock edge.

Thanks for your suggestion but it didn't work. It maybe sometime I'm doing wrong with multisim itself as I have very little experience with it.

 

Thanks for your suggestion but it didn't work. It maybe sometime I'm doing wrong with multisim itself as I have very little experience with it.

What didn't work?
How did you change the schematic?

 

The 7490 is actually two independent counters, and you have them connected incorrectly. The 555 clock goes to IN-A, and the QA output goes to IN-B.

ak

 

The 7490 is actually two independent counters, and you have them connected incorrectly. The 555 clock goes to IN-A, and the QA output goes to IN-B.

ak

Thank you very much it's working perfect now.

 

The 7490 is actually two independent counters, and you have them connected incorrectly. The 555 clock goes to IN-A, and the QA output goes to IN-B.

Ha! I thought I remembered how they work. Sorry for not checking the actual datasheet. Thanks, AK

 

The 7490 is actually two independent counters, and you have them connected incorrectly. The 555 clock goes to IN-A, and the QA output goes to IN-B.

ak

A lot of counter schematics floating around; show inA driven by Qd, you still get an overall divide by ten but the output has 50:50 mark space ratio.

 

That was the clue.

ak