Let Me See This When You Have It Working

COUNTERS Physics 427

Lab # 12

1) COUNTERS

We will examine the operation of the 74193 counter IC. The 74193 is a synchronous, up/down, 4-bit, pre-settable, binary counter. Connect the chip to +5 VDC ((pin 16) and Ground (pin 8) and connect QA, QB, QC, and QD to four LED’s. The LED’s will display the count as a binary number (keep in mind that the LED connected to QA will be the LSB of the binary number representing the count). Unless you are fluent in the binary number system you will have to convert the LED output (in your head or on paper or with a calculator) to a decimal number – the kind of number your are used to dealing with. Connect the A, B, C, and D inputs to four data switches. CLR must be connected to Ground and LOAD must be connected to +5 VDC in order for the counter to operate properly. (It is convenient to connect CLR and LOAD to data switches which are normally kept in the LO and HI states, respectively, and can be switched to the opposite states when needed.)

(a) Connect the output of another data switch to the UP input of the 74193. [Connect the DOWN input to +5 VDC – don’t let it float.] Change the switch setting from 0 to 1 and then from 1 to 0. You will observe that the counter does not count properly – it will skip a number of counts at every change of the switch setting. This is caused by switch “bounce”. Notice that the switch bounces both on the 0 to 1 and 1 to 0 transition. The number of switch bounces can be determined by observing the change in count produced by a change in the switch setting. For example, if the count jumps from 0 to 9 the switch has bounced 9 times. What is the average number of switch bounces you observe when changing the switch?

(b) Now connect the UP input of the counter to the A connection of Pushbutton A (PA). Both of the pushbuttons are debounced switches – i.e., they will not bounce when opened or closed. The A output of PA is in the HI state when the button is not depressed and in the LO state when the button is depressed. Observe how pushing and releasing PA affects the counter output. Does the counter respond to a rising or a falling edge on the UP input? The switch bounce should be gone and the counter should count properly.

Use the pushbutton switch to drive the UP input and, by successively pushing and releasing the switch, observe the counting of the 74193. Go through several complete cycles. Does the counter “roll-over” properly when it reaches 15 (i.e., does it go to zero on the next count)?

LET ME SEE THIS WHEN YOU HAVE IT WORKING.