A logic probe is a low-cost hand-held
test probe
A test probe is a physical device used to connect electronic test equipment to a device under test (DUT). Test probes range from very simple, robust devices to complex probes that are sophisticated, expensive, and fragile. Specific types include t ...
used for analyzing and troubleshooting the logical states (
boolean
Any kind of logic, function, expression, or theory based on the work of George Boole is considered Boolean.
Related to this, "Boolean" may refer to:
* Boolean data type, a form of data with only two possible values (usually "true" and "false" ...
0 or 1) of a digital circuit. When many signals need to be observed or recorded simultaneously, a
logic analyzer
A logic analyzer is an electronic instrument that captures and displays multiple signals from a digital system or digital circuit. A logic analyzer may convert the captured data into timing diagrams, protocol decodes, state machine traces, a ...
is used instead.
Overview
While most logic probes are powered by the circuit under test, some devices use batteries. They can be used on either
TTL
TTL may refer to:
Photography
* Through-the-lens metering, a camera feature
* Zenit TTL, an SLR film camera named for its TTL metering capability
Technology
* Time to live, a computer data lifespan-limiting mechanism
* Transistor–transistor lo ...
(transistor-transistor logic) or
CMOS
Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...
(complementary metal-oxide semiconductor) logic integrated circuit devices, such as
7400-series,
4000 series
The 4000 series is a CMOS logic family of integrated circuits (ICs) first introduced in 1968 by RCA. It had a supply voltage range of 5V to 20V, which is much wider than any contemporary logic family.
Almost all IC manufacturers active during thi ...
, and newer logic families that support similar voltages.
Most modern logic probes typically have one or more LEDs on the body of the probe:
* an LED to indicate a high (1) logic state.
* an LED to indicate a low (0) logic state.
* an LED to indicate changing back and forth between low and high states. The pulse-detecting electronics usually has a pulse-stretcher circuit so that even very short pulses become visible on the LED.
A control on the logic probe allows either the capture and storage of a single event or continuous running.
When the logic probe is either connected to an invalid logic level (a fault condition or a
tri-stated output) or not connected at all, none of the LEDs light up.
Another control on the logic probe allow selection of either TTL or CMOS family logic. This is required as these families have different thresholds for the logic-high (V
IH) and logic-low (V
IL) circuit
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
s.
Some logic probes have an audible tone, of which vary across models. A model may 1) emit a tone for high logic state otherwise no tone, or 2) emit a higher frequency tone for a high logic state, lower frequency tone for a low logic state, and no tone for no connection or tri-state. An oscillating signal causes the probe to alternate between high-state and low-state tones.
History
The logic probe was invented by
Gary Gordon
Gary Ivan Gordon (August 30, 1960 – October 3, 1993) was a master sergeant in the United States Army and a recipient of the Medal of Honor. At the time of his death, he was a non-commissioned officer in the United States Army's premier s ...
in 1968 while he was employed by
Hewlett-Packard
The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
.
References
External links
{{Commons category, Logic probes
Schematic of a simple logic testerHow to make a simple logic testerHow to make a logic tester using a 555 timer chipElenco logic probes
Electronic test equipment
Digital electronics
Measuring instruments