make mini logic analyzer

This mini Logic analyzer is a tool for you to watch on LCD the logic transitions 0 or 1 of a digital data signal. A digital data signal can be found on the output pin of TSOP-1730 Infrared Receiver, on the Transmit and receive pins of MAX-232 chip (RS-232), on Clock and Data pins of I2C data bus and many more electronic components. This circuit su
make mini logic analyzer - schematic

pports capturing for up to 100 kHz digital signals. The operating voltage of the circuit is 4. 8V DC from 4x1. 2V rechargeable batteries. Switch on the S1 to power on the electronic circuit. After the initial screens on LCD you will see a message that the AVR waits for a signal change on input pins. The AVR has 4 external pull-down resistors 33kG™ (R2-R5) avoiding any unnecessary trigger on any input pin because of an external electromagnetic field or by touching accidentally your hand on any input pin. The Nokia 3310/5110 LCD works from 3. 3 - 5V power supply. The problem is that the LCD`s backlight works with Maximum 3. 3V DC. So I put diodes D1-D3 to decrease the voltage from 4. 8V to 4. 8-(0. 7*3)=2. 7V that is the required power supply of Nokia`s LCD. When you power ON the circuit, the LED1 is turned OFF. After the first trigger on any of 4 input pins, this LED is turned ON and the AVR starts capturing the data in to its internal RAM buffer (290 samples). Do not use regular alcaline 1. 5V batteries instead of rechargeable. The total voltage is 4 x 1. 5 = 6V. This voltage will probably burn the LCD and the AVR microcontroller. As you can see on Picture 5 the data buffer is constituted by 870 bytes (v1. 00) 2 for the counter and one for the input pins information. In version 1. 01 the data buffer was decreased to 256*3=768 bytes for increasing the capturing speed because the buffer size variable is 8 bit instead of 16...

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