As per my previous post I still recommend you do the spectrum part with analog parts (an op amp and a few passive components are all that you need for each frequency you wish to display, if you want to go REALLY cheap then just a few passive components are all that is needed, along of course with a bargraph driver IC, but you can multiplex that), it's just much easier. You can use the pic to blank the screen's spectrum display and drive it's own sort of message. Just my opinion, but unless you WANT to do this completely digitally this is a case of the analog method simply being easier. TTYL -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Joe Denehan Sent: Saturday, June 30, 2001 12:34 To: PICLIST@MITVMA.MIT.EDU Subject: Re: [PIC]: A/D spectrum analyzer The purpose I wish to use the Spectrum Analyzer is just for a visual effect for use with any line input for music use. I would hope to use a 15-wide by 10-high LED matrix ( Lot of LED's ) and possible scroll text also, which shouldn't be too much of a problem. Can it be done? -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Robert A. LaBudde Sent: Wednesday, June 27, 2001 3:46 AM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [PIC]: A/D spectrum analyzer At 08:56 PM 6/26/01 -0600, Dan wrote: >Ages ago.... > >There was the Radio Shack Color Computer (AKA the "CoCo"), which ran at a >mere 1/4 of the >frequency of a common color burst crystal. (a 6809 @ less than 1 Mhz!). >It had >an R2R resistor ladder style D/A converter and a single analog comparator >with which one could implement an A/D in software. They sold a ROM cartridge >which contained an audio spectrum analyzer program. Does anyone else >remember this? I have a hard time believing that a clever programmer could >not achieve the same with a PIC (at 20Mhz + hardware A/D) today. The key to the whole audio spectrum analyzer question is the required bandwidth and the required frequency resolution. The RS Color Computer only measured up to 5KSPS as I recollect, and the microprocessor had an 8-bit hardware multiply. An FFT is an orthogonal transformation, so it would be possible to do a reasonable job with low accuracy fixed point arithmetic. The real killer is the memory needed for the job. A 16F877 or the like with a static ram attached would probably allow a small-scale FFT to be done. So: 1. What bandwidth? If audio, one would assume 20Hz-20kHz would be necessary. This is tough to do as a 'continuum' on a PIC. 2. What resolution in frequency? If only 8-16 individual frequencies were needed (sort of like the LED bar graph spectrum displays), then fixed frequency transforms might be viable. 3. What accuracy is needed? If only 4-bits or so, then memory requirements are much easier. If 8-bits, you need an external memory. In summary, it should be possible to do a 32-, 64- or even 128-sample DFT on a PIC, if you're willing to tolerate a less than 8-bit resulting accuracy. The maximum sampling rate would probably be only 1-2 kSPS real-time, expandable if delays in reporting are allowed (1st record, then analyze). This kind of application is much better suited to a microcomputer with a larger address space and hardware 8-bit multiply at least. E.g., 8051, etc., or better. ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: ral@lcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causas scire" ================================================================ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu