Dilshan R Jayakody’s Web Log

These days good quality oscilloscope is not an expensive instrument and, we can see it in most workbenches. With the advancement of oscilloscopes, simple testing tools such as logic probes are not as popular these days. However, if the oscilloscope or logic analyzer was out of reach, the logic probe is a handy instrument to check digital circuits.  Also, in some cases, a logic probe is an easy option to check the functionality of low-speed logic circuits because it provides a real-time visual indication of the logic state without adjustments or calibrations. Prototype version of the logic probe. The logic probe design described in this post uses common and inexpensive ICs, including the popular NE555 timer and LM393 low voltage comparator IC. At the time of this writing, both ICs were prevalent in the market and cost less than LKR50 (US$ 0.25). This circuit design using SMD components to minimize the board size. The dimensions of the soldered PCB are around 70mm × 14mm × 6.6mm, ...

This is 8 channel CMOS logic probe and pulsar which is useful when designing, testing and faultfinding in digital circuits. This circuit is designed using commonly available CMOS logic ICs which including a couple of 4069 hex inverters and 4040 binary counter. A prototype version of 8 channel logic probe and pulsar The logic probe of this system is based on 4069 hex inverters and it indicates logic high and low states with 2 LEDs. Logic pulsar of this circuit is capable to generate 12 frequencies and highest frequency it can generate is 420kHz.  This pulsar generates a square wave with 50% duty cycle and it's average rise time is 16µS. Both schematic and PCB design of this logic probe and pulsar are available to download at google drive . In this schematic, all LED-L connections should connect to the anode of LEDs and cathode should be connected to the VSS terminal of J31 ( LED-L-H ) connector. All LED-H connections should connect to the cathode of LEDs and anode must...

This is oscillator controller for 8bit PIC microcontrollers which is specifically design to debug MCUs and related circuits by without using ICD unit. This unit consists with low speed oscillator and cycle counter with automatic hold. In current version, oscillator is capable to run in 2 frequency modes and it can count up to 4096 cycles in each run. The number of frequency modes can be extend by adding more capacitors and the upper limit of cycle counter can be increase by adding more 12bit counters (and related circuitries) to the system. Oscillator waveform in low frequency mode In current version oscillator can be run in either 66 Hz ~ 70 Hz or 666 Hz ~ 670 Hz ( aprox. ). This frequency can be adjusted by changing the value of C1 or C2 capacitors (e.g: 0.1MFD can generate 6.39 kHz output signal) OR by replacing R1 with some suitable variable resistor. In project package we include sample PIC16F84A based project to test with this system. The recommended test attachment i...