;//////////////////////////////////////////////////////////////////////////// ;// ;// Ultrasonic Rangefinder Software ;// ;// Written by Gerald Coe - May 2000 ;// Tidied up for publication - 12th July 2000 ;// Adapted to PIC12F675 by JCH - October 2004 ;// Modified by PMM - May 2005 ;// includes use of nc pin for constant noise production ;// Corrected by JCH - Jan 2009 to make nc an input. ;// ;// Private and Educational use only is permitted ;// Commercial use of this software is prohibited. ;// ;//////////////////////////////////////////////////////////////////////////// list p=12f675 ; JCH include ; JCH errorlevel -302 ; JCH Suppress bank warning messages in list file __CONFIG 018Ch ; INTOSC with I/O on GP4&5, WDT Enabled, ; Power-Up Time En. JCH #define RAMSTART 20h ; JCH radix dec #define trig GPIO,0 ; trigger input from host #define pulse GPIO,1 ; timing pulse output to host #define echo GPIO,2 ; echo signals from comparator #define nc GPIO,3 ; Previously unused, now used for mode selction (sending or receiving, CTL1 on XSRF) #define tx2 GPIO,4 ; Tx phase 2 #define tx1 GPIO,5 ; Tx phase 1 #define _C STATUS,C ;///////////////////////////////////////////////////////////////////////////// org RAMSTART loop res 1 ; loop counter dlyctr res 1 ; delay counter tone_cnt res 1 ; count echo cycles period res 1 ; received burst cycle period from tmr0 flag res 1 ; PMM flag to decide how to start the signal ;///////////////////////////////////////////////////////////////////////////// org 0x000 goto jchstart ; JCH org 0x004 ; JCH insert default interrupt handler retfie jchstart: call 0x3FF ; JCH Get oscillator calibration constant bsf STATUS,RP0 ; JCH Switch to bank 1 movwf OSCCAL ; use microchip's calibration value movlw 09h ; JCH Assign prescaler to WDT, Prescale 1:2 movwf OPTION_REG ; JCH ; movlw 89h ; option ;assign 1:2 prescaler to watchdog bcf STATUS,RP0 ; JCH Switch to bank 0 clrf GPIO ; JCH Read-modify-write to clear all GPIO movlw 07h movwf CMCON ; JCH Comparator off, low power bsf STATUS,RP0 ; JCH Switch to bank 1 clrf ANSEL ; JCH ANS<3:0> all set to digital I/O movlw 0dh ; JCH Mod'd from 05h to add GPIO3 as input. movwf TRISIO ; JCH GPIO --54_3210 ; 0000_1101 (GPIO bits 0, 2 and 3 are inputs, trigger, echo, CTL1) clrf WPU ; JCH Disable all weak pull-ups bcf STATUS,RP0 ; JCH Switch to bank 0 (GPIO use) bcf pulse ;//////////////////////////////////////////////////////////////////////////// ; ; The main loop controls the range finder. In response to a low going trigger ; input, its calls "burst" to send out 8 cycles of 40khz. It then raises the ; pulse line so the host can begin timing. ; There is a choice of two tone detect routines, the simplest is currently set. ; It then clears the output pulse so the host can complete timing, and loops ; around to wait for the next cycle. ; If an echo is not detected then the watchdog timer will reset the PIC after ; about 30mS, and the pulse line will be cleared. Therefore a very long pulse ; should be interpreted as "nothing detected" main: clrwdt btfss trig ; wait for trigger signal from user to go high goto main ; from previous measurement. m2: clrwdt btfsc trig ; wait for trigger signal from user to go low goto m2 btfss nc ; PMM if nc input is low, then we are in receive mode and the PIC goto delay ; PMM should not generate any 40 kHz signal but we need to account ; PMM for the delay caused by the signal generation process comf flag,f ; 1 PMM complement the value stored in flag, store the result back in flag btfsc flag,0 ; 2 PMM if flag is clear then skip next instruction call burstA ; 1 PMM burstA will start with btfss flag,0 ; 2 PMM if flag is set then skip the next instruction call burst ; 1 send the ultra-sonic burst m3: bsf pulse ; start the output timing pulse ; OK, here's the cheap-n-easy way to detect the echo, just wait for a transition ; on the echo line. Though not really detecting a tone, it is very effective. ; The transducers provide the selectivity. ; Ignore any pulse input activity at the start (immediate echo of nearby stuff) m1: movlw 0x30 ; number of cycles in loop movwf loop ; initialize the loop counter (16) delaym11: NOP ; waste time (NOP means no operation) NOP NOP NOP NOP NOP NOP NOP NOP clrwdt decfsz loop,1 ; decrement loop and store the result back in loop ; if the result is 0, then skip the next instruction goto delaym11 ; continue loop if not finished m11: nop btfsc echo goto m11 ; wait for low bcf pulse ; end the output timing pulse ; And here is the "proper" tone detecter. It detects 3 cycles of 40khz to ; give a valid output. It works but is still experimental. It is not as effective ; as just detecting the first edge, particually in the first few cm. ; ; call tone ; validate 3 cycles of 40khz ; bcf pulse ; end the output timing pulse ; goto main ;//////////////////////////////////////////////////////////////////////////// ; ; The burst routine generates an accurately timed 40khz burst of 8 cycles. ; Since a 4Mhz PIC (1uS instruction rate) cannot generate timings of less ; than 1uS, the high half cycle is 12uS and the low half cycle 13uS. ; That's good enough. burst: clrf loop movlw 8 ; number of cycles in burst movwf loop burst1: movlw 0x10 ; 1st half cycle movwf GPIO movlw 3 ; (3 * 3inst * 1uS) -1uS = 8uS movwf dlyctr ; 8uS + (4*1uS) = 12uS burst2: decfsz dlyctr,f goto burst2 movlw 0x20 movwf GPIO movlw 2 ; (2 * 3inst * 1uS) -1uS = 5uS movwf dlyctr ; 5uS + (8*1uS) = 13uS burst3: decfsz dlyctr,f goto burst3 nop decfsz loop,f goto burst1 movlw 0x00 ; set both drives low movwf GPIO retlw 0 ;/ burstA: clrf loop movlw 8 ; number of cycles in burst movwf loop burstA1: movlw 0x20 ; 1st half cycle movwf GPIO movlw 3 ; (3 * 3inst * 1uS) -1uS = 8uS movwf dlyctr ; 8uS + (4*1uS) = 12uS burstA2: decfsz dlyctr,f goto burstA2 movlw 0x10 movwf GPIO movlw 2 ; (2 * 3inst * 1uS) -1uS = 5uS movwf dlyctr ; 5uS + (8*1uS) = 13uS burstA3: decfsz dlyctr,f goto burstA3 nop decfsz loop,f goto burstA1 movlw 0x00 ; set both drives low movwf GPIO retlw 0 ; the following subroutine will delay for 200 us delay: ;movlw 0x00 ; set both pin 2 and pin 3 to low ;movwf GPIO movlw 0x10 ; number of cycles in loop movwf loop ; initialize the loop counter (16) delay1: NOP ; waste time (NOP means no operation) NOP NOP NOP NOP NOP NOP NOP NOP NOP clrwdt decfsz loop,1 ; decrement loop and store the result back in loop ; if the result is 0, then skip the next instruction goto delay1 ; continue loop if not finished goto m3 ; return to m3 when finished ;//////////////////////////////////////////////////////////////////////////// ; ; The timing for this routine is critical. Our little PIC is only chugging ; along at 4Mhz, or 1uS per instruction. The longest path though this code ; is 19uS, out of the 25uS available - thats tight and why I only wait for a ; low on the echo line and not a high as well. tone: clrf TMR0 t1: btfsc echo goto t1 ; wait for low movfw TMR0 clrf TMR0 movwf period ; store timer0 value movlw 21 ; if(period>22 && period<30) subwf period,w btfss _C goto t2 movlw 30 subwf period,f btfsc _C goto t2 decfsz tone_cnt,f ; 25uS period OK, so goto t1 ; if not yet 3 of them, keep looking retlw 0 ; else - success - return t2: movlw 3 ; failed to detect 25uS period, so reset tone detect movwf tone_cnt ; to 3 and keep looking goto t1 ;//////////////////////////////////////////////////////////////////////////// end ;////////////////////////////////////////////////////////////////////////////