Hello Guys,

I am trying to do a simple digital electronics project where I put two seven segment displays and once I connect the voltage source, the displays start counting automatically from 00 to 99.

Here is a video of exactly what I want to do:

http://www.youtube.com/watch?v=74IdmCIvk5s

My group and I found the attached schematic which we think is what we need to build to make the circuit in the video.

We built it, but the displays just show two values which sort of look like "A", and it doesn't change.

I was wondering, could someone tell me if that particular schematic does what I want to do?

What is the use of the timer? Is that what increments the values from 00 to 99??

What is the use of the potentiometer? To adjust frequency?

Thank you all very much!

 

That circuit has a 555 astable to provide a clock frequency to increment the counter. The pot does indeed adjust the frequency.

The counter is two 4026 decade counters with decoded outputs to drive 7-segment common-cathode LED displays. I haven't checked the circuit for errors but, if there are none and you wired it correctly, then it should work.

Is the display a common-cathode type as required?

Do you have access to an oscilloscope to look at the circuit waveforms?

 

That circuit has a 555 astable to provide a clock frequency to increment the counter. The pot does indeed adjust the frequency.

The counter is two 4026 decade counters with decoded outputs to drive 7-segment common-cathode LED displays. I haven't checked the circuit for errors but, if there are none and you wired it correctly, then it should work.

Is the display a common-cathode type as required?

Do you have access to an oscilloscope to look at the circuit waveforms?

Yes, the Seven Segments have common cathodes as required.

Is there a way to see if the 555 timer works with a multimeter instead of an oscilloscope?

Thank you very much for your feedback. At least my group and I now know we are on the right track.

 

If you crank R2 to its maximum value, the frequency should be low enough for you to see a fluctuation with a multimeter on the DC range at pin 3 output. At higher frequencies you should also be able to see a voltage on the AC range.

 

Is there a way to see if the 555 timer works with a multimeter instead of an oscilloscope?

Just connect an LED with a current-limiting resistor, say 330Ω or so if using 6V, to pin 3 of the 555. Put the anode of the LED on pin 3, connect the LED cathode through the resistor to GND. If the 555 is working, you'll see the LED flash. Be sure to turn the pot to both extremes slowly - if the pot is set too high or low and you don't move it, the LED could appear off or on all the time.

Also, add a 0.1uF capacitor to across Vcc and GND on each and every IC. Add an additional 1uF electrolytic capacitor across Vcc and GND on the 555. This helps eliminate noise.

Post a picture or two of your physical circuit as well, we may be able to spot something.