Author Topic: Networked RTC FP Display  (Read 1586 times)

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Offline croberts

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Networked RTC FP Display
« on: March 07, 2013, 06:51:51 pm »
At some point while designing the Solar Powered LED lighting system for my home, I decided it would be nice if the master controller knew what time of day it was. That was the inspiration for the Networked RTC FP Display board design. I decided to use an LED display so I could drive the display directly from the PIC16F690. The display is multiplexed so the circuit doesn’t demand much power but there is provision on the board to manually blank the display by removing jumper JP5. Because the circuit can be used as a real time clock or a floating point display there is another hardware provision on the board (JP4) to allow for the display of either a colon or decimal points. Pins are limited when you are using a 20 pin PIC so for real time clock applications two jumpers (JP1 and JP2) and a trimpot are used to set the time. A 3 pin connector can be installed in place of the trimpot in floating point display applications to allow for the connection of a local analog signal to the PIC for ADC. The displayed information does not have to be local because the board can be connected to the half duplex network in my lighting system so the displayed number can be from network data. The schematic shows circuitry for a half duplex network but those of you who read my topic know the circuit can be easily converted to use full duplex.

When this circuit is used as a real time clock, accuracy is bound to be a concern. The real time clock is using the internal oscillator of the PIC as a timebase so tolerance and drift as a result of temperature, aging, etc can affect the accuracy of the clock. For my application, I’m not concerned about near perfect clock accuracy and the circuit is installed in a room temperature environment. The clock does keep time fairly well and from time to time when it crosses my mind I reset it as required. I have a provision in the software to add or subtract seconds per hour to help compensate for the small inaccuracy of the PIC internal oscillator. I’m sure some additional measures could be implemented in software to improve accuracy.

If you are curious about the state machines in the assembly file, please read my post

Attached are the following files;
Networked RTC FP Display schematic as pdf
Networked Real Time Clock code as asm*
Networked Real Time Clock installation as jpg**
*Columns may not appear as intended if not viewed in MPLAB editor.
**Shows 2" x 2" PCB installed in 4" electrical box

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