ECE 220 PreLab

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ECE 220 Pre-Lab

• Lecture 1

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Knowing Your GTA
John Jackson E-Mail johnj_at_email.arizona.edu Of
fice ECE 320 - Carrel 5 Office Hours MW 10
1130, Thur 2 - 3
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Pre-Lab Report

• Use green/yellow engineering paper
• Can be handwritten
• Use Stockroom Coversheet
• Class web-site under Laboratory section
• Grading for each part is on web-site
• Also under Laboratory section
• Must submit to attend the lab
• Even if it is late (giving TA time to grade)
• 1 day late 50 off

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To Give and To Receive

• Turn in to the Stockroom
• Due on Friday at 400 PM
• Graded report returned in lab

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Resistor Color Code
Silver
Directly Multiply by first 2 bands. All other
cases, 3rd band tells the number of zeros.
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Resistor Color Code

• 4th band is the tolerance
• Brown is 1 tolerance
• Red is 2 tolerance
• Gold is 5 tolerance
• Silver is 10 tolerance
• No band is 20 tolerance

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Resistor Color Code
Brown Black Brown Gold 10 1 zero 100 Ohms 5
Tolerance
Red Black Gold Gold 20 x 0.1 2 Ohms 5 Tolerance
Blue White Orange Silver 69 3 zeros 69
kOhms 10 Tolerance
Violet Brown Yellow Silver 71 4 zeros 710
kOhms 10 Tolerance
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The Loading Effect
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The Loading Effect
R5 (R3 R4) R2 R3 R4 500k 500k
1M 1M R2 1M 1k 1M 1k (1M x 1k) /
(1M 1k) 1M 1k 999 Ohms Because R1 and R5
are almost equal, so is the Voltage across them.
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The Loading Effect
The result shows we were correct. Now lets look
at the big picture again.
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The Loading Effect
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The Loading Effect
-2.499 I(500k) I(500k) 0 I(1M) 2.499 I
2.499 / 1M I 2.499 uA V4 R4 x I 500k x
2.499u V4 1.2495 V V1 / 4 5 / 4 1.25 V
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The Loading Effect
Shouldnt this give divide by 4 also?
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The Loading Effect
Nope. It doesnt.
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Balanced Bridge
R4 is usually a variable resistor (potentiometer).
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Balanced Bridge
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Dimmer Circuits
Each pot is 10k
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Questions?

• The only stupid question is the one you didnt
  ask!!!

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The End

• See you 2 weeks from now
• Keep an eye on class site