Logic tester
The logic tester is an electronic measuring device and is used to display logical states (0 or 1) in digital circuits. It usually has a pen-like structure and is held in the hand for measurements. At the front end there is a fine measuring tip - similar to a probe head - with which the conductor point to be measured is touched.
The logic tester is normally supplied with voltage from the circuit to be tested. For this purpose, there is a flexible cable on the back that ends in two crocodile clips . Some logic testers are also battery-operated, but still require a ground connection that is connected to the circuit to be tested. Levels can be measured in CMOS and TTL circuits. Since these circuits define different voltage levels for the logic states, the logic tester must be set to the circuit before starting the measurement.
The logic level is displayed using two light-emitting diodes, usually in different colors (for example red / green) for easier differentiation. High-quality devices also signal the logic level with an acoustic signal (high / low tone).
Depending on the equipment variant, there are other functions:
- Pulse display: an additional light emitting diode makes signal pulses or oscillating signals visible.
- Pulse generator: A short pulse can be "injected" into the circuit. The logic tester can drive up to 100 mA into the circuit, but the pulse duration is usually limited to a few microseconds so that the integrated circuits are not destroyed.
- Memory function: A single pulse is displayed permanently until the display is reset.
- Counter: A simple binary counter with mostly 4 LEDs.
Since logic testers can only display individual signals, they are not suitable for use in complex digital circuits with data buses or high clock frequencies (over 20 MHz). Logic analyzers are used here, for example .
