74192 garage counter

Hi there. I am working on my capstone. We have created an up/down counter to attach to a sensor so as to count cars going into and out of a parking garage. While our circuit is working, I would however like the count up to stop at 120, and the count down to stop at 000. I would also like the reset button to reset to 120, if it is possible. Right now when it comes on in multisim, it starts the count at 999 and can roll up or down past 000/999. I have no idea how to successfully modulate the 74192 IC's. Any suggestions would be greatly appreciated. Here is a copy of my multisim circuit:

 

Instead of clearing the count on reset, load the counters with 120, or whatever number you want.

Multisim is an idealized representation. The counts will come up in any state(count) unless it's taken care of in the device (not likely). So, don't count on coming up at 999.


What do you mean by modulate the 74192 ICs? Do you mean multiplex?

 

I mean have a modulus or trunciated count of 120. As it is now, the count is to a full 999. To change the count means to create some kind of feed back to the input from the output of a flip flop or binary counting device like the 74192 and expect a specific count.

 

If all you want is a mod-121 counter, activate clear when count is greater than 120.

 

Or, detect the count has reached 120 and disable further UP count inputs. I assume the parking garage has 120 spaces. If you really wanted to get fancy, a count of 120 could cause the 7 segment displays to flash FULL

 

Since OP stated he wants the clear button to load in 120, I would assume 120 is the empty reading indicating capacity ready to be filled.

 

You can use a NOR gate to detect when all BO inputs are low (a NOR gate goes high when all inputs are low), which indicates all counters are at zero. You can use this signal to stop the count or do whatever else you want to do at when the counter reaches zero.

 

Gathering all the informations from the feedbacks, I came out with the schematic attached.

The random number at power-up was taken care of with the "power-up reset" circuit.

But there is one problem I cannot understand. After power-up, though the counters show "000" at the outputs, the 3-input NOR doesnt inhibit the input (7408) of the down counter, until I presed the DOWN button once. Only then all the "BO" became LOW.

After that if I pressed the UP button, the outputs of the counter becomes "990". I have to press the UP button 10 times for it to become "000" again. Is there any clue why this happens?

Allen

[edit] attachment removed [/edit]

 

Sorry, I just couldnt resist.

Hope this is not a homework project...

Allen

 

The schematic is removed. Luckily, Angela is not online at the moment...

Sorry..