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74hc393 and 74hc4040

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apl247

New Member
I am having trouble getting these two binary counters to work properly. I am not getting the output as expected.

I have the Vcc connected to a 5V power supply and having the reset output connected to the Vcc to reset the counter and then I wire it to the common ground for 0. When I input my clock pulses, I am not getting the output as expected. After the first clock pulse, I will get an output of 110 or some other number that is not 1. The same thing happens when I input a 2nd clock pulse, the output is some random number.

I am inputting the clock pulses manually (as in I have a wire in the clock input and place it in the Vcc and then remove it, the oscilloscope is showing a clean pulse output). I have also tried using a function generator for the clock pulses, but the same thing happens.

Why is the counter not counting as it should? Am I missing something?
 

barf

New Member
Make sure your CLR inputs are not floating. Tie them high with a 10K resistor.

If you are clocking yourself, you are probably getting bounce which registers as several clocks. Use a debounce circuit in front of the clock input. Use a couple of cross-connected logic gates to debounce - Use google to look up circuit.
 

Mikebits

Well-Known Member
Post your schematic.
 

apl247

New Member
I don't have a schematic, I am just testing the chip itself on a breadboard, with Vcc tied to a 5V power supply, and the ground pin tied to a common ground row. I am inputting the clock pulse manually, and measuring the DC voltage at each of the output pins.
 

Mikebits

Well-Known Member
You can't clock the pin with a wire to VCC as you will get contact bounce. If you use a function gen it should work but clock frequency should be very low so you are only clocking 1 pulse per second or so. Read about switch bounce here.

http://www.ganssle.com/debouncing.pdf
 

AllVol

New Member
I am inputting the clock pulses manually (as in I have a wire in the clock input and place it in the Vcc and then remove it, the oscilloscope is showing a clean pulse output). I have also tried using a function generator for the clock pulses, but the same thing happens.

Why is the counter not counting as it should? Am I missing something?

According to its data sheet, the 74x4040 requires an active low pulse to clock, instead of your active high. Check the d.s. for the other chip to see if its requirement is not the same.
 
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