webmasterpdx wrote:> First, filtering using an embedded 8-bit micro is possible. Ignore people > who are talking double precision, etc, etc....they aren't embedded people > with experience in this area. I have invented an algorithm that works well > on a PIC (8-bit also). I call it the "tri-band filter". I had a situation > where I had to generate a measure of the power spectrum in 3 bands in an > audio spectrum of a piano (about 4.5KHz). So, I took 32 samples at a time > (I was limted by memory) and ran a FIR filter on the data. I basically > chose a FIR filter of the form ax0+bx1+cx2 and centered it at the midpoint > of my frequency range. My sample rate was twice the highest frequency (by > Nyquist). > Now, I used some online filter coefficient generator. What I noticed is > the LPF coefficients were the same as the HPF coefficients just swapping > signs here and there, so as long as I calculated ax0, bx1 and cx2, I could > use the same calculations for both filters. The second trick I used was to > round any floating point values to the nearest powers of two. For example, > one term was 0.3664, and I rounded it to 0.375 (3/8*x), which can be > calculated as ((x << 2) + x) >> 3, which involves no multiplies (my PIC > didn't have a multiply) and only involves integer calculations. Note that > the frequency response of the filter (if you choose your coefficients > carefully) was almost identical to the non-altered one and my results were > very accurate (much better than my older state variable filter that I used > to use). If you combine the touching of coords to be combinations of power > of two so you can do your calculations using shifts and adds and reuse > coefficients to give you both High and Low pass results simultaneously. The > band pass was obtained by subtracting the LPF and HPF values from the > original data. You will need to use a 16 bit accumulator (assuming you are > using 8-bit sampled data) and remember to shift left and add BEFORE > shifting right as you'll get more accurate results that way. > This algorithm works very well for 8-bit processors. > Enjoy...You do realize that this is a year-old thread? Whatever, you seem like the kind of pragmatic programmer I admire. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
FIR filter in 8051 micro
Started by ●October 30, 2007
Reply by ●October 20, 20092009-10-20
Reply by ●October 20, 20092009-10-20
webmasterpdx <webmasterpdx@gmail.com> wrote:> First, filtering using an embedded 8-bit micro is possible. Ignore people > who are talking double precision, etc, etc....they aren't embedded people > with experience in this area.Well, a large fraction of DSP is done in 16 bit fixed point. In that case, double precision might be 32 bit fixed point, not so hard to do on an 8051. Floating point in any precision is probably not the best choice for DSP on an 8 bit processor. -- glen
Reply by ●October 20, 20092009-10-20
glen herrmannsfeldt wrote:> webmasterpdx <webmasterpdx@gmail.com> wrote: >> First, filtering using an embedded 8-bit micro is possible. Ignore people >> who are talking double precision, etc, etc....they aren't embedded people >> with experience in this area. > > Well, a large fraction of DSP is done in 16 bit fixed point. > In that case, double precision might be 32 bit fixed point, not so > hard to do on an 8051. Floating point in any precision is probably > not the best choice for DSP on an 8 bit processor.As far as I remember, the 8051 doesn't have a carry test. (But there's always a way ...) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●October 20, 20092009-10-20
On Oct 20, 4:10�pm, Jerry Avins <j...@ieee.org> wrote:> glen herrmannsfeldt wrote: > > webmasterpdx <webmaster...@gmail.com> wrote: > >> First, filtering using an embedded 8-bit micro is possible. Ignore people > >> who are talking double precision, etc, etc....they aren't embedded people > >> with experience in this area. > > > Well, a large fraction of DSP is done in 16 bit fixed point. > > In that case, double precision might be 32 bit fixed point, not so > > hard to do on an 8051. �Floating point in any precision is probably > > not the best choice for DSP on an 8 bit processor. > > As far as I remember, the 8051 doesn't have a carry test. (But there's > always a way ...)does it have an Add with Carry instruction? maybe the OP's sample rate is real slow. r b-j
Reply by ●October 21, 20092009-10-21
Yeah, I know it's an old post, but I want to help anyone who might come across that to know that this kind of stuff is possible. It does take a pragmatic approach. One area I try to evangelize is that I see a lot of newer engineers coming out of university with experience using XSCALE processors and PCs with unlimited resources and often these people never lived in the age of the slow mainframes, slow CPU modules or even slow CPUs. Mostly it's about prices and time to market. As a result, we often have to get very creative with what we have, and if we can do something with a $1 uP instead of a $10 DSP or $30 XSCALE, then we should go for the $1 uP. Of course when you play with new algorithms you invent, by all means simulate it. I simulated the filter before using it both on my TI-86 and then later in C (where I could simulate 8-bit calculations) and gnuplot to plot the results. I created input signals that were combinations of sine waves at different frequencies added up, and the results were pretty darn accurate. Not the perfect simulation, but good enough for me. Then in the prototype product, it worked just fine. Coming up with clever ways to measure and condition our signals forms the core of innovation in small embedded projects as they usually involve measuring some quantity to give results that can be used elsewhere. e.g. If using a uP with a crystal clock, the most accurate measurement you can make is that of time (width of a pulse), so if you want to measure capacitance or inductance, tying that to a circuit that measures rise time will give you much better results than trying to measure the quantity itself. Another example, if not unusual.....I was tasked with measuring velocity of rollerblades. The problem was that using light was a problem due to mud, etc, being thrown up. So, instead we measured sound and autocorrellation. The idea being that the front blades will go over the same bumps as the back blades, so an autocorrelation should show a bump for each wheel, so if you know the distance between the wheels you can determine the velocity. It wasn't quite that simple and there are faster ways of doing autocorrelations than a multiply accumulate (average minimum differences) that only involves subtracts and adds. Bottom line, the technique worked. I guess what I'm saying is that you can often (more often than people realize) do it with a PIC or 8051, just as well as with an XSCALE or full DSP, and I encourage people to do that when possible. Thats all. Of course, there are occasions when you do need double precisions (ill conditioned equations, etc, etc), but these, for me, are last resorts... Thx -D
Reply by ●October 21, 20092009-10-21
On 21-10-2009 at 11:19:22 webmasterpdx <webmasterpdx@gmail.com> wrote: What you are describing is in my country called engineering and so called "inventions" are just called in my country basic knowledge and thinking. And what you did with coefficients is called scalling (more or less). There is absolutely nothing exciting and nothing unusual in such everyday work. It takes 2-3 yrs to become such inventor :). -- Mikolaj
Reply by ●October 21, 20092009-10-21
Mikolaj wrote:> On 21-10-2009 at 11:19:22 webmasterpdx <webmasterpdx@gmail.com> wrote: > > What you are describing > is in my country called engineering > and so called "inventions" > are just called in my country > basic knowledge and thinking. > And what you did with coefficients is called scalling > (more or less). > > There is absolutely nothing exciting > and nothing unusual > in such everyday work. > It takes 2-3 yrs to become such inventor :).Nevertheless, the approach is rare enough to be admired anywhere in the world. I come from an industry where redesigning a circuit to make it a penny cheaper without reducing performance -- often performance was actually improved -- would bring a substantial bonus at year's end. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
