Post by thread:[PIC]: Synchronised dual freq generator

Hi all, My current project involves generating a signal between 10 and 1000 Hz, both square wave and sine (possibly also triangle). What I want to do for min parts count is use one CCP module to generate say a 50kHz square wave and use that as the clock signal to a LP filter with a 50:1 clock-to-Fcorner ratio. The same signal is used as input to a timer/counter, to divide it by 50. The result of that (1kHz) can be used as is (square wave), or run through the filter to get a sine wave. Problem I have is getting the div by 50 signal at a PIC output pin. As far as I can see, I can use the 'special event' of the 2nd CCP, but I can only either set, clear or leave alone the output pin. There apparently is no way to toggle the output pin. Or am I overlooking something? Thanks for any advice, Jan Didden -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Use the CCP2 interrupt to change the polarity of the NEXT CCP2 event. You have plenty of time between edges to set this up and latency won't cause jitter since the edge change is done with the hardware timing. SkinTech wrote: {Quote hidden}> > Hi all, > > My current project involves generating a signal between 10 and 1000 Hz, both > square wave and sine (possibly also triangle). What I want to do for min > parts count is use one CCP module to generate say a 50kHz square wave and > use that as the clock signal to a LP filter with a 50:1 clock-to-Fcorner > ratio. The same signal is used as input to a timer/counter, to divide it by > 50. The result of that (1kHz) can be used as is (square wave), or run > through the filter to get a sine wave. Problem I have is getting the div by > 50 signal at a PIC output pin. As far as I can see, I can use the 'special > event' of the 2nd CCP, but I can only either set, clear or leave alone the > output pin. There apparently is no way to toggle the output pin. Or am I > overlooking something? > > Thanks for any advice, > > Jan Didden > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Hi Jan, I have just been working on some code that uses a 50:1 clock to cutoff ratio chip and I had to produce a 750Hz - 50000Hz clock to give a cut-off frequency range of 15 - 1000Hz. Very similar to what you want but without the divided by 50 output. I looked at using the CCP module to produce the square wave, as Robert Rolf suggested each CCP interrupt changes the polarity of the next CCP event so the output pin toggles state each time. The problem in my case was I had too much other stuff going on with interrupts and it was going to get all messed up especially at the higher frequencies. I suggest it is probably a very good method if you have no other interrupts enabled. Oh for a multi level interrupts! In the end I used the PWM mode to generate my square wave, switching the prescaler between 1:1, 1:4 and 1:16 to get the best resolution over the full range. Anyway, once you have produced your 500 - 50,000Hz square wave using the CCP, it should be pretty easy in the interrupt routine to increment a variable and when it gets to 50 toggle the state of an output. Hey presto a divided by 50 output. Brent Brown Electronic Design Solutions 16 English Street Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile/text: 025 334 069 eMail: .....brent.brownKILLspam.....clear.net.nz -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

No DAC needed. Just use the internal PWM at up to 76KHz sample rate at 8 bits per sample. Since your highest frequency is 1Khz you wouldn't need a very steep filter on the output (perhaps just an simple RC). Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) {Original Message removed}

Bob, Thanks, yes I can see now how to approach this. Never used the CCP/PWM before so will generate some cursing, oh well.. I probably can approximate the square wave with a trapezium, controlling the rise times etc. Did I mention I need a way to offset the wave, so have to add varying amounts of DC. I can see a lot of look-up tables in this. Initially I thought that the filtering woyuld give problems due to the large freq span (10Hz to 1KHz), but I guess I will keep the pwm freq constant so a single filter freq is needed. Also thanks to other people that gave me valuable hints (Herbert, Brent, Robert). Jan Didden {Original Message removed}