Build Your Own Logic Probe: A Simple 3V-5V Circuit

Circuit diagram

This schematic represents a Logic Analyzer. It determines the logical state of any TTL logic circuit’s point. For operation, the device requires supplying power matching the circuit being examined – identical Vcc and GND supplies are necessary. To ascertain the logical level, the "Test" wire of the analyzer must be connected to the specific node within the circuit under inspection.

Integrated Circuit – CD4016

The CD4016 is a versatile 14-stage binary ripple counter integrated circuit. This IC employs static CMOS technology, offering excellent noise immunity and speed. It’s commonly used for timing applications, generating waveforms, and as a building block in more complex digital circuits. Its core functionality involves propagating a clock signal through its stages, creating a cascading effect. The CD4016 has a power supply voltage range of 3V to 5V, and the outputs are typically TTL compatible. It is a popular choice for educational purposes and hobbyist projects due to its low cost and readily available documentation.

If the signal level is Low, the device will show a “zero” (0) and solely the green LED will illuminate. When the signal level is High, the device will display a “one” (1) and only the red LED will shine. If the signal level is Impedance, the device will show nothing and no LED will be activated. The logical state is "Low" when the “Test” wire is connected to the ground of the circuit (the voltage is between 0V and 2V). The logical state is "Impedance" when the “Test” wire is unconnected (it has no voltage or the voltage is between 2V and 3V). The logical state is "High" when the “Test” wire is connected to the positive supply of the circuit (the voltage is between 3V and 5V).