In this project we were able to use all of the concepts and skills that we have developed when working on synchronous counter designs. We had to use these skills to build a Now Serving Display as you would see in a DMV or at a Deli Counter.
-Paper and Pencil (For sketches)
-Circuit Design Software (MultiSim was used)
>Common Cathode Seven-Seg Displays
>Additional logic gates as needed
- The two output displays are common cathode seven-segment displays
-Current limiting resistors (150 ohms - 270 ohms) must be used
-Each display will use a 74LS48 BCD-To-Seven-Segment display driver.
-The counting is controlled by two cascaded 74LS193 Synchronous 4-Bit Binary Counters
-Any additional logic may be used as needed to support the counter designs.
I simply started by looking back at previous assignments using MSI counters. You could almost directly use the circuits from 3.3.3 and the 60 sec display. With the MSI counter you just had to change few of the outputs with an inverter and change the inputs from power to ground to get the desired number count. I built a quick version in MultiSim (to the left) to test my theory. Once i did that i had to adjust a few things, at first the display wasn't working. This is because i had accident used a common anode instead of common cathode.
Circuit Design Software Implementation
How does it work? To put it in simpler terms... The circuit consists of two MSI 193 gates that are almost identical. The ABCD inputs are all wired to ground to give them a input of 0. The 4 input NAND gate (on both the ones and tens place) is the reset line that is set to reset on 10.
I doubled up with Colton Laird to wire this project, we worked together to design the circuit and as we were working on our game board project after school, we took a break to finish this up. It ended up glitching out here and there, but i believe it was because of battery power and breadboard malfunction. The circuit also had D-Bounce. So after shown how to we inserted D-Flip flops to eliminate the bounce. It was a long tedious time spent wiring.