Elenco Logic Probe Kit User Manual
LOGIC PROBE KIT
MODEL LP-525K
Assembly and Instruction Manual
Copyright © 2013, 1994 by Elenco®Electronics, Inc. All rights reserved. Revised 2013 REV-J 753241
No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.
ELENCO
®
Qty. Symbol Description Part #
! 1 D6 1N4002 Diode 314002
! 5 D1 - D5 1N4148 Diode 314148
! 2 Q2, Q4 2N3904 Transistor 323904
Qty. Symbol Description Part #
! 3 Q1, 3, 5 2N3906 Transistor 323906
! 1 U1 LM2901 IC 332901
! 3 L1 - L3 LED 350001
SEMICONDUCTORS
Qty. Symbol Description Part #
! 1 C2 100pF (101) Discap 221017
! 1 C3 200pF (201) Discap 222010
! 2 C1, C6 0.001µF (102) Discap 231036
Qty. Symbol Description Part #
! 1 C4 0.005µF (502) Discap 235018
! 1 C5 0.047µF (473) Discap 244780
! 1 C7 0.1µF (104) Discap 251010
PARTS LIST
If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this LP-525K Logic Probe Kit from a distributor, catalog, etc., please contact ELENCO
®
(address/phone/e-mail is at the back of this manual) for additional assistance, if needed. DO NOT contact your
place of purchase as they will not be able to help you.
RESISTORS
Qty. Symbol Description Color Code Part #
! 3 R21, R23, R24 200Ω 5% 1/4W red-black-brown-gold 132000
! 1 R16 2kΩ 5% 1/4W red-black-red-gold 142000
! 1 R4 4.7kΩ 5% 1/4W yellow-violet-red-gold 144700
! 1 R14 5.1kΩ 5% 1/4W green-brown-red-gold 145100
! 1 R11 15kΩ 5% 1/4W brown-green-orange-gold 151500
! 1 R13 18kΩ 5% 1/4W brown-gray-orange-gold 151800
! 2 R10, R15 20kΩ 5% 1/4W red-black-orange-gold 152000
! 2 R12, R22 30kΩ 5% 1/4W orange-black-orange-gold 153000
! 7 R1, R5 - R8, R19, R20 100kΩ 5% 1/4W brown-black-yellow-gold 161000
! 1 R17 120kΩ 5% 1/4W brown-red-yellow-gold 161200
! 1 R18 150kΩ 5% 1/4W brown-green-yellow-gold 161500
! 3 R2, R3, R9 4.7MΩ 5% 1/4W yellow-violet-green-gold 174700
CAPACITORS
-1-
Qty. Description Part #
! 1 PC board 517014
! 2 Switch SPDT 541024
! 1 Probe tip 616001
! 1 Case 623005
! 2 Screw #4 x 5/8” 643450
! 1 IC socket 14-pin 664014
! 1 Label front 724002
Qty. Description Part #
! 1 Label back 724003
! 1 Wire 1.5” 814220
! 1 Power cord 862102
! 3” Tubing #20 890020
! 1” Shrink tubing (red) 890312
! 1 Solder tube lead-free 9LF99
MISCELLANEOUS
Resistor
PARTS IDENTIFICATION
Diode
Capacitor Transistor
Integrated Circuit LED
IC Socket
Case Top
Case Bottom
Probe Tip
Switch
Power Cord
-2-
Warning:
If the capacitor is
connected with
incorrect polarity, it
may heat up and
either leak, or
cause the capacitor
to explode.
IDENTIFYING RESISTOR VALUES
Use the following information as a guide in properly identifying the value of resistors.
BANDS
METRIC UNITS AND CONVERSIONS
Abbreviation Means Multiply Unit By Or
p Pico .000000000001 10
-12
n nano .000000001 10
-9
µ micro .000001 10
-6
m milli .001 10
-3
– unit 1 10
0
k kilo 1,000 10
3
M mega 1,000,000 10
6
1. 1,000 pico units = 1 nano unit
2. 1,000 nano units = 1 micro unit
3. 1,000 micro units = 1 milli unit
4. 1,000 milli units = 1 unit
5. 1,000 units = 1 kilo unit
6. 1,000 kilo units = 1 mega unit
IDENTIFYING CAPACITOR VALUES
Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or µF (microfarads).
Most capacitors will have their actual value printed on them. Some capacitors may have their value printed in
the following manner. The maximum operating voltage may also be printed on the capacitor.
Electrolytic capacitors have a positive
and a negative electrode. The
negative lead is indicated on the
packaging by a stripe with minus
signs and possibly arrowheads. Also,
the negative lead of a radial
electrolytic is shorter than the positive
one.
Polarity
marking
BAND 1
1st Digit
Color Digit
Black 0
Brown
1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Gray 8
White 9
BAND 2
2nd Digit
Color Digit
Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Gray 8
White 9
Multiplier
Color Multiplier
Black 1
Brown 10
Red 100
Orange 1,000
Yellow 10,000
Green 100,000
Blue 1,000,000
Silver 0.01
Gold 0.1
Resistance
Tole r ance
Color Tol eran ce
Silver ±10%
Gold ±5%
Brown ±1%
Red ±2%
Orange ±3%
Green ±0.5%
Blue ±0.25%
Violet ±0.1%
1
2 Multiplier Tolerance
Multiplier
For the No. 0 1 2 3 4 5 8 9
Multiply By 1 10 100 1k 10k 100k .01 0.1
(+)
(–)
(+)
(–)
Axial
Radial
Second digit
First digit
Multiplier
Tolerance*
Note: The letter “R” may be used at times
to signify a decimal point; as in 3R3 = 3.3
The letter M indicates a tolerance of +20%
The letter K indicates a tolerance of +10%
The letter J indicates a tolerance of +5%
Maximum working voltage
(may or may not appear
on the cap)
The value is 10 x 10 =
100pF, +10%, 50V
*
CERAMIC DISC MYLAR
First digit
Second digit
Multiplier
Tolerance*
2A222J
100V
The value is 22 x 100 =
2,200pF or .0022µF, +5%, 100V
101K
50V
-3-
SPECIFICATIONS
Input Impedance 1MΩ
Input Overload Protection 35V DC continuous
Thresholds Logic 1 Logic 0
TTL 2.3 + .25V 0.80V + .1V
CMOS 70% Vcc 30% Vcc
Response better than 25 nanoseconds
Pulse Detector 1.5 millisecond pulse stretcher
Power Requirements 5V Vcc @ 30mA
15V Vcc @ 40mA
Operating Temperature 0OC to +40OC
CIRCUIT DESCRIPTION
The Elenco®Model LP-525K Logic Probe kit is a
convenient and precise instrument for use in the
measurement of logic circuits. It displays logic
levels (high or low), and voltage transients down to
25 nanoseconds. The LED readouts provide instant
response to the logic state.
To detect the high and low logic levels, the LP-525
uses two comparators of a Quad Comparator
LM2901 Integrated Circuit (see schematic diagram).
One comparator drives the HI LED and the other
drives the LOW LED. The comparator output goes
low, lighting the LED, when the (–) input is more
positive than the (+) input. To measure TTL circuits,
the TTL-CMOS switch is set to TTL and the red and
black alligator clips are connected to +5VDC and
ground. The (+) input (pin 5) of the HI comparator is
then biased to 2.3VDC by resistor network R9
through R15. Thus, the LED lights when the probe
tip is more positive than 2.3VDC. To measure
CMOS circuits, the HI comparator changes to
3.5VDC or 70% of the supply voltage.
The (–) input of the LOW comparator is biased to
0.8VDC for TTL operation and 1.5VDC or 30% of
the supply voltage for CMOS operation. The LOW
LED thus lights when the probe tip is connected to
voltages less than 0.8 or 1.5VDC.
The pulse LED is controlled by a bipolar edge
detector circuit which responds to both positive and
negative transients. This circuit is made up of
capacitors C2 and C3, transistors Q1 through Q4,
and the associated resistors. When the circuit is
activated by pulses as short as 25 nanoseconds, a
negative pulse is applied to the (+) input (pin 11) of
the pulse stretcher comparator. The comparator
then turns on and is held by the feedback resistor
R8. The ground level on the output (pin 13) causes
C5 to discharge through R17. In approximately 1.5
milliseconds, the voltage on the (–) input (pin 10)
becomes more negative than the (+) input and the
comparator turns off. The short pulse on the input is
thus stretched to 1.5 milliseconds.
The (–) input (pin 8) of the PULSE LED driver is
biased to +2.5VDC by resistors R19 and R20. The
(+) input is biased to +3VDC by resistors R6 and
R18. The 1.5 milliseconds pulse from the pulse
stretcher grounds the (+) input through diode D5
turning the comparator on and lighting the PULSE
LED. When the PULSE-MEM switch is in MEM, Q5
is also turned on, causing the (–) input of the
comparator to go to +5VDC. This keeps the
comparator on even after the (+) input returns to
+3VDC. When the PULSE-MEM switch is in
PULSE, the feedback path to the (–) input is broken
and the LED is lit only for the duration of the 1.5
milliseconds pulse.
Thus, each time the input signal changes state, the
PULSE LED is activated for 1.5 milliseconds. When
observing low frequency signals, the PULSE LED
provides an immediate indication of this pulse
activity. By observing the HI and LOW LEDs, the
polarity of the pulse train can be determined. Low
frequencies cause the PULSE LED to blink once for
each transition. High frequencies cause the LED to
flash at a rate that makes it appear to be on
continuously. When the PULSE-MEM switch is in
MEM, a single input pulse will cause the PULSE
LED to come on and stay on until the switch is
returned to the PULSE position.
The input impedance of the LP-525 is 1MΩ. This
eliminates any loading effect on the circuit under
test.
CAUTION: Do not connect the alligator clips to any
AC power source or to a DC power source greater
than 35VDC. Failure to comply with this warning
may result in damage to this instrument.
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