http://www.8051projects.net/ Learn to make simple microcontroller projects, pic, 8051, avr and arm projects. download 8051 projects, tutorials, libraries, sample codes. join the microcontroller discussion forum and ask doubts regarding electronics. the best source for 8051 over internet. en-gb 2009-01-07T21:54:04-08:00 contact@nospam.com hourly 1 2000-01-01T12:00+00:00 http://www.8051projects.net/forum-t7667.html 2009-01-07T21:54:04-08:00 post your doubts herehttp://www.8051projects.net/forum-t7669-last.htmlhello everybody...as an embedded enthusiast.. we all know the importance of external signals received by the micro-controllers/proccessors...most of the time these signals are analog in nature. in such cases we usually go for ADC'sto convert these physicall quantities to digital...further sometimes you are required to generate analog signals from the digital data u already have.. ex. MP3 player. in such case we go for the DAC.these ADC's and DAC's are supposed to be accurate.. but there are certain abonamilities that creep in... these may render your data useless..for the precaution , therefore we go for signal conditioning circuits!!these signal conditioning are nothing but filters used to reduce ripples..and noise content..now we all know that there are certain limitations to hardware as well as software....here comes the concep of DSP algorithms.....certain high quality embedded products use DSP(proccessors ) as co-proccessors to their main proccessors/controllers...these DSPs have certain features that enables them to be used for very fast and very complex calculations including imaginary value arithmetic...still there are some signal proccessing algorithms that we can implement easily in our controllers / proccessors.. to give them that product like feel...so here i am requesting all your contribution to this coloumn by submitting your signal proccessing algorithms plus doubts in them ... before we start: this is how u shud select your ADC:Successive approximation A/D converters are used routinely in applications of 1 MHz or less. For higher rates, parallel or flash converters are used. These perform comparisons in parallel. The hardware is more complicated, but the conversion time is much smaller. The number of bits per sample are more limited (typically 12 bits or less), but the sample frequency range can extend into the 1 GHz range (useful for digital communications systems). Flash converters can be cascaded to achieve better performance. http://www.8051projects.net/forum-t7667.html 2009-01-07T21:54:04-08:00 shyam SAMPLE AND HOLD FUNDAMENTAL please refer to the above circuit and any doubts please post @http://www.8051projects.net/forum-t7669-last.htmlref: http://www.ece.msstate.edu/ http://www.8051projects.net/forum-t7667.html 2009-01-07T21:54:04-08:00 shyam NOISE cud be of some help too ... well we all always are against the noise increpency to the signal...!!!some times it (noise) can come out to be of great help...for a better reading/understanding you shud read some tpoics about spread spectrum techniques.. these are actually carried out in frequency domain.. since it is not easy in our gud old 51 to compute comlex numbers(imaginary part), we tend to work in time domain.. so here i shall be discussing the use of noise in time domaun only!lets move a little ahead of the sample hold technique..assume sample rate to be 5 / secrun a loop so that to read 5 adc data in 1 sec.suppose u get 3.3v 2.9v 3.7v 2.4v 2.8v...take average of these values u get.. 3.02vso u can just write adc0=3.02vadc1=3.02vadc2=3.02vadc3=3.02vadc4=3.02vnow let us add a fixed noise thru code.. suppose u r adding 10v noise thru code.. i.e.the values will change to 13.3v 12.9v 13.7v 12.4v 12.8vtaking average u get 13.46now let us reduce the noise..we get 13.46 -10=3.46 v... !!!!!try the above example over and over and u will find that the latter one (with noise ) will get u a better representation of data...hint what if a spike creeps in making one of the data to 6v?? try for your self!!