shared wiring: pic

Saturday, July 13, 2013

Digital Alarm Clock Using PIC

This project describes a digital clock with alarm function. It uses a PIC16F877 microcontroller to generate an accurate 1 sec delay with Timer0 using Roman’s zero error method. The time is displayed in large size font on a 4×20 character LCD that uses HD44780 display driver. You can synchronize the time with your computer time through a serial port.

Digital Alarm Clock Using PIC Circuit Diagram

The required power is provided through a 9 V wall adapter which is used to obtain a regulated +5 V power supply using a LM7805 IC. The microcontroller runs with a 20 MHz external clock. The backlight of LCD is driven by a PWM output from the microcontroller so that the back light intensity can be varied. The full software written in JAL is available to download. Source Code.

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Tuesday, July 9, 2013

USB Powered PIC Programmer

This simple circuit can be used to program the PIC16F84 and similar "flash memory" type parts. It uses a cheap 555 timer IC to generate the programming voltage from a +5V rail, allowing the circuit to be powered from a computer’s USB port. The 555 timer (IC1) is configured as a free-running oscillator, with a frequency of about 6.5kHz. The output of the timer drives four 100nF capacitors and 1N4148 diodes wir-ed in a Cockroft-Walton voltage multiplier configuration.

Circuit diagram:

USB-Powered PIC Programmer Circuit Diagram

The output of the multiplier is switched through to the MCLR/Vpp pin of the PIC during programming via a 4N28 optocoupler. Diodes ZD1 and D5 between the MCLR/Vpp pin and ground clamp the output of the multiplier to about 13.6V, ensuring that the maximum input voltage (Vihh) of the PIC is not exceeded. A 100kΩ resistor pulls the pin down to a valid logic low level (Vil) when the optocoupler is not conducting. The circuit is compatible with the popular "JDM" programmer, so can be used with supporting software such as "ICProg" (see http://www.ic-prog.com).

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