Logic probe

The logic tester is an electronic measuring device and is used to display logic states (0 or 1) in the digital circuits. It is constructed mostly similar pin and is held to measure in hand. At the front end is a fine probe tip - similar to a probe - with the measured head office is touched.

The voltage supply of the logic tester is usually from the circuit to be tested. For this purpose, located on the back of a flexible line which ends with two alligator clips. Some logic tester are also battery-operated, but will still need a ground terminal is connected to the circuit to be tested. You can measure levels in CMOS and TTL circuits. Since these circuits define different high voltage level for the logic states, the logic tester must be adjusted to the circuit prior to the start of the measurement.

The display of the logic level is determined by two LEDs, mostly executed for easier distinction in different colors (eg, red / green). High-quality devices signal the logic level in addition by an acoustic signal ( high / low tone ).

Depending on the trim level you will find more features:

• Pulse indicator: An additional LED makes signal pulses and oscillating signals visible.
• Pulse: A short pulse can be " injected " into the circuit. The logic tester can drive up to 100 mA in the circuit to quite, but the pulse duration is most limited to a few microseconds, so that the integrated circuits will not be destroyed.
• Memory function: A single pulse is permanently displayed until the display is reset.
• Counter: A simple binary counter with mostly 4 LEDs.

Since logic testers can only show single signals, they are not suitable for use in complex digital circuits with data buses or high clock frequencies (above 20 MHz). Here logic analyzers are used for example.