ENGINEERING 182   BASIC ELECTRONIC CIRCUITS LAB 4

 

   THE FOLLOWING INSTRUCTIONS, DIAGRAMS, AND QUESTIONS ARE MEANT TO HELP YOU UNDERSTAND ABOUT BASIC ELECTRONIC CIRCUITRY.  YOU MAY CONSTRUCT THE CIRCUITS BY REFERRING TO ANY WRITTEN PROCEDURES, OR TO SCHEMATIC DIAGRAMS, OR TO BOTH DEPENDING ON YOUR PREFERENCES.  IT IS RECOMMENDED THAT YOU USE WRITTEN PROCEDURES FOR THE DEBOUNCE CIRCUIT (THE FIRST CIRCUIT OF THIS LAB), HOWEVER, YOU ARE EXPECTED TO CONSTRUCT THE PHOTOCELL CIRCUIT (THE SECOND CIRCUIT OF THIS LAB) BY REFERRING ONLY TO THE SCHEMATIC DIAGRAM.  ALSO, IF ANY CIRCUIT DOES NOT WORK AS EXPECTED, OR ANY COMPONENT GETS HOT TO THE TOUCH, UNPLUG THE POWER SUPPLY AND RE-CHECK YOUR WIRING !  ASK FOR HELP BEFORE SPENDING TOO MUCH TIME DEBUGGING ON YOUR OWN.

 

1.           LOCATE the following PIECES and PARTS in your ELECTRONIC PARTS KITS or on the TABLE:

 

A power supply with wire leads, a Digital Multi-Meter (DMM), a switch, an LED, three 100 Kohm resistors (brown/black/yellow), a 330 ohm resistor (orange/orange/brown), three 1 Kohm resistors (brown/black/red), a blue trim potentiometer, a 0.01 mF capacitor, a 1 mF capacitor, a 10 mF capacitor, a 2N2222 transistor, a digital counter display, a NE555 Timer (8 pin IC), an LM324 Quad Comparator (14 Pin IC), a photocell, a wire jumpers kit, and a prototyping board.

 

2.           UNPLUG the power supply from the electrical outlet.

 

3.           Choose a convenient location for the NE555 TIMER (8 Pin IC) and carefully press the pins of that IC into the prototyping board.  The IC should STRADDLE ONE OF THE GAPS in the prototyping board.  Insure you can IDENTIFY THE LOCATION OF PIN 1 on the IC.

 

4.           On the prototyping board, CONNECT one LEAD of the SWITCH to a GROUND hole (blue line).  CONNECT the other LEAD to an available hole in the 5-hole terminal set that has IC PIN 2 as part of the set.

 

5.           CONNECT a 100 Kohm RESISTOR from that same set to +5 VOLT POWER bus (red line).

 

6.           CONNECT a 0.01 mF CAPACITOR from the hole set of IC PIN 5 to GROUND (blue line).

 

7.           CONNECT a JUMPER WIRE from the hole set of IC PIN 1 to GROUND (blue line).

 

8.           CONNECT a JUMPER WIRE from the hole set of IC PIN 4 to +5 VOLTS (red line).

 

9.           CONNECT a JUMPER WIRE from the hole set of IC PIN 8 to +5 VOLTS (red line).

 

10.       CONNECT a VERY SHORT JUMPER WIRE from the hole set of IC PIN 6 to the hole set of IC PIN 7.

 

11.       CONNECT a 100 Kohm RESISTOR (brown/black/yellow) from the hole set of IC PIN 6 to the POWER bus (red line).

 

12.       CONNECT a 10 mF CAPACITOR from the hole set of IC PIN 7 to GROUND (blue line).  Insure the LEAD MARKED WITH A NEGATIVE SIGN is CONNECTED to GROUND (blue line).

13.       INSERT the 2N2222 TRANSISTOR in a convenient board location ACROSS THREE UNUSED HOLE SETS.

 

 

14.       CONNECT a 1 Kohm RESISTOR (brown/black/red) from the hole set of IC PIN 3 to the hole set of the MIDDLE LEAD (‘B’) OF THE TRANSISTOR.

 

15.       CONNECT a 100 Kohm RESISTOR (brown/black/yellow) from the hole set of TRANSISTOR LEAD ‘E’ to GROUND (blue line).

 

16.       INSERT the CONNECTOR FROM THE DIGITAL COUNTER DISPLAY across FOUR UNUSED HOLE SETS NEAR THE TRANSISTOR.

 

17.       CONNECT a JUMPER WIRE from the hole set of TRANSISTOR LEAD ‘E’ to the hole set of the DIGITAL COUNTER DISPLAY CONNECTOR PIN 1 (SILVER MARK).

 

18.       CONNECT a JUMPER WIRE from the hole set of TRANSISTOR LEAD ‘C’ to the hole set of the DIGITAL COUNTER CONNECTOR PIN 3.

 

19.       CONNECT LEADS from the POWER SUPPLY to the prototyping board.  INSURE that the POSITIVE LEAD goes to the GREEN POST while the NEGATIVE LEAD (ground, GND, or COM) goes to the BLACK POST.  At the same time, CONNECT JUMPER WIRES from the POSTS to the POWER BUS sets.  The +5 (GREEN POST) should wire to the RED STRIPED sets while the GROUND (BLACK POST) should go to the BLUE STRIPED sets.

 

20.       INSURE THE RESPECTIVE POWER BUS SECTIONS (RED AND BLUE)  ARE PROPERLY JUMPERED TO PROVIDE POWER TO ALL BUS SECTIONS OF THE PROTOTYPING BOARD.  INSURE RED IS JUMPERED ONLY TO RED AND BLUE ONLY TO BLUE !!

 

 

21.       PLUG IN the POWER SUPPLY to the 120 Vac ELECTRICAL OUTLET.

 

22.       SET the DMM to a 20 Vdc range (three ‘clicks’ counterclockwise from OFF position).

 

23.       CONNECT (HOLD) the BLACK PROBE OF THE DMM to the BLACK POST ON THE POWER SUPPLY.  ALL READINGS WITH THE DMM SHOULD BE TAKEN WITH ITS BLACK PROBE CONNECTED TO THE BLACK POST OF THE POWER SUPPLY !!!

 

24.       TOUCH the RED PROBE OF THE DMM to IC PIN 4.  The DMM should READ ABOUT 5 VOLTS.  TOUCH the RED PROBE OF THE DMM to IC PIN 8.  The DMM should READ ABOUT 5 VOLTS.  (Any time you do not get the stated readings, unplug the power supply and recheck your wiring).

 

25.       WHILE VIEWING THE DIGITAL COUNTER DISPLAY, PRESS AND RELEASE the SWITCH LEVER.  The COUNTER DISPLAY READING should INCREMENT BY ONE.  (IF THE READING DOES NOT CHANGE, UNPLUG THE POWER SUPPLY AND RECHECK YOUR WIRING).  Also, the BUTTON ON THE FRONT OF THE DIGITAL COUNTER DISPLAY is used to RESET the DISPLAY TO ZERO.  

 

26.       MAKE the following VOLTAGE MEASUREMENTS using the RED PROBE of the DMM:

 

a.       IC PIN 2 with SWITCH RELEASED  …………………..._______________ Volts

b.       IC PIN 2 with SWITCH LEVER PRESSED AND HELD _______________ Volts

c.       IC PIN 3 with SWITCH RELEASED  ……………………_______________ Volts

d.       IC PIN 3 with SWITCH LEVER PRESSED AND HELD _______________ Volts

 

27.       WHILE TOUCHING IC PIN 3 with the RED PROBE, PRESS AND IMMEDIATELY RELEASE THE SWITCH LEVER and TIME HOW LONG THE DMM READING STAYS CHANGED FROM ITS INITIAL VALUE.   ___________________  seconds.

 

28.       SET the DMM to OFF and UNPLUG THE POWER SUPPLY.

 

29.       INCLUDE THE ABOVE READINGS IN YOUR LAB REPORT !

 

30.       UNPLUG THE POWER SUPPLY.  CONSTRUCT THE PHOTOCELL CIRCUIT SHOWN BELOW.  NOTE this circuit uses the debounce circuit you just completed except the switch input is replaced by additional circuitry.  The circuit should give a count pulse each time the light beam from the LED to the photocell is interrupted.


31.       You are expected to construct this final circuit by reference to the schematic diagram above.  If help is needed, ask your TA or Instructor.

 

32.       IMPORTANT NOTE:::  An adjustment must be made to the reference voltage at IC LM324 PIN 2 for proper operation to occur.  This adjustment is performed as follows.  If ALL WIRING IS CHECKED, PLUG IN THE POWER SUPPLY.  SET the DMM to a 20 Vdc range (three ‘clicks’ counterclockwise from OFF position).

 

TOUCH THE RED PROBE to IC LM324 PIN 3 and NOTE THE VOLTAGE.  ___________volts.  Now, BLOCK THE LIGHT BEAM and NOTE THE VOLTAGE at the SAME POINT _____________volts.  CALCULATE and NOTE the average value of the two readings _____________  volts.  TOUCH the RED PROBE to IC LM324 PIN 2.  WATCH the READING at that point and ADJUST the BLUE TRIM POTENTIOMETER until the voltage reading is NOMINALLY THE AVERAGE VALUE you just calculated.  (What you have done is set a reference voltage that is used by IC LM324 to compare an input signal to.  The input signal is the voltage variation due to light changes at the photocell.  The output signal of IC LM324 (PIN 1) will be ‘low’ (less than 0.5 volts) when the input signal is lower than the reference voltage, and will be ‘high’ (greater than 1.6 volts) when the input signal is greater then the reference voltage).  With the adjustment made, the circuit should now properly count each time the light beam is interrupted.

 

33.       VERIFY and NOTE the TIME DURATION OF THE OUTPUT PULSE at IC 555 PIN 3 as being about the same time as with the isolated debounce circuit.                        _________ seconds.

 

34.       As a FUN exercise, UNPLUG THE POWER SUPPLY and replace the 10 mF CAPACITOR with a 1 mF CAPACITOR from your kit.  Insure the polarity is observed.  PLUG IN THE POWER SUPPLY.  What difference do you see in the operation of the photocell circuit?_________________________________________

 

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35.       UNPLUG THE POWER SUPPLY and TURN OFF THE DMM !!!

 

36.       Have a member of your team DRAW the PHYSICAL LAYOUT of your CIRCUIT on the handout prototype board sheet provided.

 

37.       INCLUDE THE ABOVE READINGS and SKETCH IN YOUR LAB REPORT !

 

38.       You have COMPLETED the HANDS-ON PORTION of the LAB !!