Miniature Real-Time Controller using PIC16F84




Introduction
The F84 MRTC was my second design of a miniature real-time controller. This version uses PIC16F84 running with a low power X-tal 32,768Hz. The scheduler for 6-channel output was saved in EEPROM. No terminal for serial downloading of the scheduler. It’s suitable for fixed scheduler job. Two AA size battery provides +3V backup for clock operation when main power has failed. Time setting at 19:00 is set only once by pressing S1 button. The 6-channel open collector output provides max. 30mA @30V load.

Real-Time Controller

Hardware

A circuit diagram of the F84 MRTC is shown in Figure 1. The controller is  PIC16F84, Flash based RISC uController running with a low-power X-tal 32,768Hz. The 6-channel output is RB2 to RB7 connected to a 74LS07 open collector buffer providing approx. 30mA @30V suitable for driving a homemade opto-triac shown in Miniature Real-time Controller 2051 version. D1 and D2 forms a simple switch between main supply and +3V battery. As can be seen, D1 may be silicon signal diode 1N914 or 1N4148. D2, however, can use a Ge diode having lower V forward. S1 is a momentary switch when pressed, it set current time to 19:00. The small LED at RB0, indicates functioning of the controller, after reset the blink rate is 1Hz, after press S1 set time to 19:00, it will blink at 1/3Hz or every 3 second.

Software
The original source program for the F84 MRTC was written using ‘C’, RTC.C with header file RTC.H. The hex file, RTC.HEX was compiled by PICC PCW V2.666. Daily scheduler is resided in 64-byte EEPROM data space. Editing for your scheduler can be made under PicPro by Nigel Goodwin. As shown in Figure 2, each byte may edit and enter into Nigel’s Picpro buffer before write the code and EEPROM data into the F84 chip. See details of setting scheduler in RTC.C

 

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