SHEFFIELD ENGINEERING CENTRE
NVQ LEVEL 2 PEO – UNIT 36 ASSEMBLING AND TESTING ELECTRONIC CIRCUITS
Testing Task
Using your completed 555 Timer circuit take several readings across points
indicated on circuit diagram above.
555 Timer Circuit
Measure the Voltage between points A and B Volts.
A) Write down the reading shown on your multi-meter ___________ Volts
Check the switch is working – connect between A and C - operate the switch.
B) Write down the voltage when the switch is on __________Volts
Check the 555 timer chip has power. What voltage do you expect?
__________ Volts.
Connect the black lead to D and the red lead to E.
C) Write down the voltage __________ Volts.
Connect between A (black lead) and G (red lead). Is there a reading? yes/no.
D) What you notice about the reading on your meter?
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NAME:………………………………….
DATE:……………………..
SHEFFIELD ENGINEERING CENTRE
NVQ LEVEL 2 PEO – UNIT 36 ASSEMBLING AND TESTING ELECTRONIC CIRCUITS
Connect between A (black lead) and H (red lead).
E) Write down the voltage readings ________ Volts. What is happening to
the voltage, how does this affect the LED’s?
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By connecting an oscilloscope A (Negative) and H (Positive) it is possible to
see the shape of the wave created
F) Draw the wave you see from the oscilloscope below. Describe what is
happening.
Now connect the oscilloscope probes to the negative leg of the capacitor
(Black Lead) and the positive leg of the capacitor (Red Lead).
G) Draw the wave you see from the oscilloscope below. Describe what is
happening.
NAME:………………………………….
DATE:……………………..
SHEFFIELD ENGINEERING CENTRE
NVQ LEVEL 2 PEO – UNIT 36 ASSEMBLING AND TESTING ELECTRONIC CIRCUITS
You are now required to check the current in your circuit. This will require
you to break part of your circuit.
Explain how and where you did this, and write down the value you have for
the current.
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555 Timer, connected to the 4026 driving the 7 Segment
Display
Using your existing 555 timer circuit, connect the counter part of the circuit
(the 4026 chip and the seven segment display)
Task:
1) Are the chips is inserted the correct way round if unsure please ask.
How do you know it is the right way around?
2) Use the logic probe to check what is happening at pin 3 of the 555
timer. What is happening? Explain why.
3) Move the logic probe to pin 1 of the 4026 chip. What is happening
here? Use you workbook to help by looking at page 26.
4) Would you expect pin 3 of the 4026 to be HI or LOW? Explain why.
NAME:………………………………….
DATE:……………………..
SHEFFIELD ENGINEERING CENTRE
NVQ LEVEL 2 PEO – UNIT 36 ASSEMBLING AND TESTING ELECTRONIC CIRCUITS
5) Check you have the correct output state at pin 8 and 16. What should
they be?
Go round each of the output pins on the 4026 with your logic probe and check
that each is on and the correct segment of the display is working. If a segment
of the display is not working or is incorrect then check each of your
connections. YOU MAY NEED TO SWITCH THE PROBE TO TTL IF YOU
DONT GET THE EXPECTED OUTPUT
6) Look at the table below. This shows the segments needed for each
count from 0 to 9. Can you think of any other numbers/characters you
could produce? Fill in the following table if you can. Add any more you
can think of!
Outputs from the 4026 counter and display
driver IC
Count
1
2
A
C
4
E
F
a
b
c
d
e
f
g
7) Check the action of the reset switch. If it does not function use your
logic probe to find out why.
NAME:………………………………….
DATE:……………………..