LOGIC PROBE

**LP-1 Logic Probe**

The logic probe is an economical and useful device for testing a logic circuit. It displays HIGH and LOW and a PULSE with different colored LEDs and audible signals at voltage test points of a digital circuit. Therefore, the logic probe is a tool that lets you peek inside CMOS and TTL/LS integrated circuits.

SPECIFICATIONS
Thresholds	TTL/LS	CMOS/MOS
Thresholds	LO = 0.8V HI = 2.25V	LO < 30% Vcc HI > 70% Vcc
Input Impedance	100k ohm
Minimum Detectable Pulse Width	50 ns
Maximum Input Frequency	10MHz
Pulse/Normal	Switch Selectable
Power Supply Max. Stand-by Current	10mA at 5V 30mA at 15V
Maximum Operating Current	20mA at 5V 80mA at 15V

Circuit Description

The probe tip of an LP-1 Logic Probe is connected to a dual threshold window comparator and a bi-polar edge detector. The window comparator bias network establishes the LOGIC "1" and LOGIC "0" threshold levels. The levels are fixed in the DTL/TTL mode (2.25 Volts and 0.8 Volts) in the CMOS/HTL mode the thresholds are detemined by the applied Vcc Voltage - LOGIC "1" > 70% Vcc, LOGIC "0" < 30% Vcc.

The bipolar edge detector responds to both positive and negative transitions and drives a pulse stretcher circuit. The pulse stretcher converts level transistions as well as narrow pulses to 1/3 of a second pulses that drive one of the three readout LEDs. In the memory mode, the output of the edge detector is fed to a latching flip-flop.

Video Clips

Connecting a Logic Probe for use (856 KB)
Using a Logic Probe (1.0 MB)