SirPic - Lab» Frequency Counter via IrTx

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Project:	Frequency Counter via IrTx
Source Code:	PIC Assembler
PIC:	16F628
Interface:	IrTx
Author:	Ravi Deo
Last Updated:	7th April 2005

Project Description:

This sample PIC project demonstrates how to use a PIC 16F628 with SirPic, to implement the core functionality of a frequency counter. Display output from the PIC is transmitted via the IrTx interface to SirPic running on the Palm.

SirPic displays the calculated frequency as the decimal value "f=<frequency> Hz".

Project Download:

Frequency counter via IR : Zip file containing ASM and HEX files (approx 4KB).

Hardware Schematic:

With this PIC project an external 4MHz external clock oscillator is used to drive both the PIC, and also as a convenient test signal for counting the frequency (test signal feeding pin 12 of the PIC). The Infra-red bit-stream output from the PIC (pin 8) feeds the SirPic IrTx Infra-red transmitter unit .

Schematic

Source Code

This project makes use of the 16F628's 16 bit TIMER1 as an asynchronous counter, counting the number of rising pulse edges over a duration of 1/X of a second. The pre-scaler is set to 1:1, so multiplying the count by X, gives the frequency count in Hertz. Using values of X as 2^N (eg X=1,2,4,8,16...) helps simplify the multiplication operation (double the number by shifting bits left 1 bit).

The code comprises of the following subroutines:

InitPic:     Initialises the PIC device
MainLoop:    Main loop which counts and displays frequency
FreqDelay:   Interval X over which frequency is counted
DoubleFreq:  Multiplies 1 32-bit frequency count by two
TxChIr:      Standard SirPic subroutine to transmit char via Infra-Red
WaitDelay:   Standard SirPic delay routine used by above
SkipZero:    Skips leading zero digits
ShowDigit:   Displays the frequency digit
bcd2a:       Converts BCD to ASCII
b2bcd:       Converts 32-bit Binary to BCD

SirPic Settings

SirPic Communication and Options settings should be configured as shown below (Note Text mode):

16f628

SirPic Output

On starting the SirPic log session, you should see the following data being captured.

16f628

Try disconnecting the input signal to pin 12 and watch the frequency drop to zero.