Logic_Probe.Eloctronic_Circuit_Presentation.ppt

it is slide about logic probe

1. Nurlan Hasanov
Logic Probe

2. Lamp OFF … LOGIC LOW
Lamp ON … LOGIC HIGH
Lamp DIM … OPEN CIRCUIT (FLOATING) OR BAD LEVEL
(Other brands of probes may differ)

3. A logic probe works by indicating the logic level present at the
probe tip. If the lamp is off, it signifies a logic low level. If the
lamp is on, it indicates a logic high level. If the lamp is dim, it
suggests an open circuit, a floating signal, or a bad level. Different
brands of logic probes might have slight variations, but the
fundamental principles remain the same

4. 0
10
60
50
80
70
40
30
20
100
90
HIGH
LOW
Digital logic levels as % of V
SUPPLY
HIGH
TTL CMOS
(5 V supply) (3 to 18 V supply)
% of V
SUPPLY
UNDEFINED
UNDEFINED
LOW
= 1 = ON
= ? = FLOATING
= 0 = OFF

5. Digital logic levels are defined as a percentage of the
supply voltage. For TTL logic levels, a high is typically
above 2V and a low is below 0.8V. For CMOS logic
levels, which can have supply voltages ranging from 3V to
18V, a high is usually above 70-80% of the supply voltage
and a low is below 20-30%. Undefined levels can indicate
floating or indeterminate states.

6. Common faults that can be detected with logic probes
Open bond
(floating output)
Internal short
(stuck high)
Solder bridge
(stuck low)
Defective input

7. Logic probes can detect several common faults in digital
circuits. These include open bonds, which result in floating
outputs; internal shorts that cause signals to be stuck high;
solder bridges that cause signals to be stuck low; and defective
inputs. Identifying these issues quickly is crucial for effective
troubleshooting.

8. Logic probe with pulse memory
(often used to catch “glitches”)
1. Set TTL/CMOS switch
to family under test.
2. Place tip on circuit
under test.
3. Press MEM/CLR
(light goes out).
4. Light comes on when
a single pulse (“glitch”)
occurs.

9. Some advanced logic probes come with a pulse memory feature,
which is useful for capturing transient events or glitches. To use
this feature, set the TTL/CMOS switch according to the family
under test, place the probe tip on the circuit, press the MEM/CLR
button to reset the memory, and observe the light. The light will
turn on when a glitch is detected, indicating the presence of a
single pulse

10. Pulse trains cause the probe to flash at less than a 10 Hz rate
even if the pulse frequency is much higher. (up to 80 MHz)
This probe will “stretch” pulses as
short as 10 ns and the lamp will flash.

11. Logic probes can also detect pulse trains. Even if the pulse
frequency is much higher, the probe will flash at a rate of less
than 10 Hz. This probe can 'stretch' pulses as short as 10
nanoseconds, causing the lamp to flash and indicating the
presence of high-frequency signals up to 80 MHz. This is
particularly useful for detecting rapid changes in digital
signals

12. THANK YOU