Complementary Output Generator (COG)

[David Stephenson]

I've been looking at the datasheet for the 16F1705 and controlling this module at first (and even second) look is daunting - just so many options in so many registers. Anyway many of these setting are not on closer examination relevant to getting the thing working. So I've managed to take the PWM3 output (set to 40kHz and 50% duty cycle) and feed it into the COG module to output two complimentary waveforms (on RC4 and RC5). I intend to drive an ultrasonic tranducer using the square wave from these two pins.
Below is the code it may get you started if you feel to use this module.

~~~~~~~~

chip 16LF1705,8

config OSC=INTOSC, MCLRE=Off, WDT=off, boren=off

unlockpps
RC5PPS = 8 'coga > RC5
RC4PPS = 10 'COGC>RC4
lockpps

INIPWM3
INICOG

do
wait 5 sec
SET COG1ASD0.7 OFF
wait 5 sec
SET COG1ASD0.7 ON
loop

SUB INIPWM3
ccptmrs=b'00000000' 'select timer2 for all
pwm3con=b'00000000' 'clr reg
pr2=49 'set period 40 kHz
pwm3dch=25 '100 ->50%
pwm3dcl=0 'set duty cycle
pir1.1=0 'clr interrupt timer2
t2con=b'00000100' 'start timer
dir portc.5 out 'enable PWM pin
set pwm3con.7 on 'enable PWM3
END SUB

SUB INICOG
'INITIALIZE COG FOR HALF BRIDGE OUTPUT
'ON CHANNELS COGA AND COGC USING PWM3
SET PWM3CON.7 OFF 'DISABLE PWM
dir portc.5 in 'disable COG pin
DIR PORTC.4 IN
COG1CON0=B'10001100' 'ENABLE,FOSC,HALF BR
COG1DBR=0 'NO RISING DELAY
COG1DBF=0 'NO FALLING DELAY
COG1CON1=B'00000001' 'POLARITY COGA REVERSED
COG1BLKR=0
COG1BLKF=0
COG1PHR=0
COG1PHF=0
COG1ASD1=0
COG1ASD0=B'10001000' 'COG OFF A&C OFF
SET COG1RIS.6 ON 'PWM3 SOURCE
SET COG1FIS.6 ON 'PWM3 SOURCE
COG1RSIM=0
COG1FSIM=0
DIR PORTC.5 OUT
DIR PORTC.4 OUT
SET COG1ASD0.7 OFF 'COG ENABLE
SET PWM3CON.7 ON 'ENABLE PWM
END SUB

~~~~~~~~~

[stan cartwright]

Is the idea to give the us transducer more output? I've seen 555 circuits that use push-pull to drive us tx,

[David Stephenson]

Yes thats the idea I'm using 2xAA batteries so there's not a lot of voltage to work with.
The receiver is picking it up remarkably well so I may not have to use much amplification.
My goal is to make an ultrasonic anemometer.

[stan cartwright]

Good on you sir,very not my thing but nice you picked GCB as a dev option. Thanks for the code, it is pasted for future ref. Anti phase square wave is 4 times more I read.Like a 12v car amp that gives more than 3W. Intrigued about your project I can only say I spent a lot of time many years ago building the reciever end for us sensors and it never worked.. alas. I still have 2 sets of matched sensors...neither is called tx or rx. Those ebay sensors are very good since they are a rip off of a pic circuit,like the one I tried to get working on vero
edit anemometer? half spheres windmill?
edit 2 the speed of wind...yes,sounds brill but in reality...us sensor??? ok they work at the speed of sound and wind isn't that fast so....???