Engneering 2

Building and Testing a Simple Electronic Circuit with Flashing LED's Rodrigo Valdez, Nathan Collins Prepared by Rodrigo Valdez

Objective: The goal of Experiment #1 is to construct a simple Flashing LED electronic circuit to acquaint those new to electronic circui t building with soldering components onto a printed-circuit board (PCB), identifying resistors and their values using their color codes and get an overall feel of electronic circuit function.

Schematic:

Equipment/Supplies

• Flashing LED Kit #147580 (product #MK102)

• Nine-volt battery

• Soldering Toolkit

• Small soldering irons and soldering iron stands

• Wood soldering surface

• Stopwatch

• Calculator

Procedure:

For this lab a Flashing LED Kit #147570 (MK102) was built using the circuit schematic and component

outlines on board, this allowed for proper component insertion. The resistors were the first components

attached; their values were compared to the schematic for proper placement of the 1OK O and 1K 0

resistors. The direction of insertion of these resistors was not important. Resistors leads were bent into

place, ensuring a close fit without damage, soldered and excess ends clipped. Remaining components

(transistors, capacitors, potentiometers and LEDs) were positioned next, paying close attention to their

polarity, soldered to board and excess wire was clipped. Last component attached was the battery

connector wires, once attached connected to 9V battery to ensure circuit was working properly. The

flashing LEDs were then timed and adjusted to record maximum, minimum flash times, as well as how

many flashes in a minute.

Data Tables

Flash Time

Flash Time Seconds

Maximum 2.14

Minimum 0.264

One-Minute Flash Timing

Try Flashes

1 53

2 52

3 52

One Potentiometer set to max and one set to minimum for 1 minute

Time Flashes

1 Minute 53

Both potentiometers set to minimum for 5 seconds

Time Flashes

5 Seconds 19

Calculations

Due to the difficulty to record the timing for minimum flash time, one potentiometer was set to max and

one to minimum flash times, counted amount of flash cycles in a minute, subtracted that from 60 seconds and

divided the result by the amount of flash cycles we achieved. That will result in the amount of time for one led to

blink at minimum flash time, to get timing for a full cycle, that result is multiplied by 2.

60s (1 minute) - 53 (flashes)= 7

7 / 53 = 0.132

0.132 x 2 = 0.264 seconds

Another method to calculate the minimum flash time was to count number of flash cycles in 5 seconds with both

potentiometers set to minimum, divide by 5 seconds and take the inverse of the frequency to get the period

19 (flashes)/ 5s = 3.8 = frequency

T = 1 / f

T = 1 / 3.8 = 0.263 seconds

Graphs

Maximum and Minimum flash time (in seconds)

Number of Flashes in One Minute

Results and Conclusions

After some trial and error with practicing soldering components to a PCB, success was obtained in

building a fully functioning Flashing LED electronic circuit. The experiment enabled a better understanding of the

circuit building process, identifying components and the importance of properly placing them on the PCB for full

functionality. Using the potentiometers to adjust flash times of the LEDs, helped in seeing how potentiometers

work and their affect on the circuits functioning. The experiment also included the opportunity to use period (T)

and frequency (!) in calculating flash times, in a very simple manner that greatly helps in understanding these

concepts.

Laboratory Questions

1. Maximum flash time of both LEDs:

2. Minimum flash time of both LEDs:

2.14 seconds

0.264 seconds

3. One-minute flash timing: How many flashes did each LED make (should be Close to 60)?

a. Try 1: 53

b. Try 2: 52

c. Try 3: 52

4. How consistent was the flash cycle?

The flash cycle was fairly consistent, there were some variations but the fluctuation was not of great

magnitude.

5. How easy was it to adjust the timing of the LED flash cycle?

It took a few tries to get it right, it was difficult to be very precise as the adjustments had to rely on

humans approximation and not scientific instrumentation precision.

6. List any problems in soldering.

At first it was difficult to work in such a compact area, the components are so close together that there

is not much room for error. Tinning took some time getting used to but it definitely helped in the long

run as once in a groove it was easier to solder the components to the PCB.

7. List any other problems in building the electronics kit:

Working with such minute objects was difficult at first, but after reviewing the schematic it was easier

to plan around what components to place first in order to maximize the area on the board provided.

Avoided incorrect placement of components, after reviewing the schematic, matched up the

components with their outline on the board and using the color code on the resistors.

8. List lessons learned (other than soldering):

It is very important to review schematics to make sure components are placed correctly on the board

to avoid issues with polarity. Resistor insertion direction (not placement) on boa rd is immaterial.

9. What is the tolerance of the resisters in the LED flasher kit? Both types of resistors have gold bands

on them meaning they have a tolerance of 5%