Filter circuit for the MAX1270?

MarkS

The concept of filtering signals is pretty foreign to me. I'm beginning to understand how caps work is this regard, but the input filter for an ADC is far more complicated than a simple cap. While I understand what caps and resistors do, trying to understand why the engineer arranged the dozen or so of them the way he/she did is like trying to decipher Latin.

There are two things I desperately need here. One is a good reference to BASIC filter design (internet, book, whatever...) and two is a good circuit that I can play around with in the interim. Can anyone help me in this regard?

Thanks,
Mark

LoopyByteloose

Filters can be a huge topic with lots of exotic math, or you can simplify it down to a 'cookbook' approach.

First of all, there a passive filters - those that use just resistors, capacitors, and coils.
And then there are active filters - those that use Op Amps.

You need to select your flavor too - low pass, high pass, notch [noparse][[/noparse]a band passing filer], or blocking [noparse][[/noparse]a band blocking filter].

Often with an ADC, what you need is a simple passive, low pass filter to eliminate high frequency noise from causing false reading. In many cases, a resistor and a capacitor will suffice.

I suggest you take a look at NEETS. This is the complete Electronics course for Navy Technicians and it is good because it is written for first timers and it is FREE. While it does not explicitly present a whole text on filters, the texts on Waveforms and Modulation will be useful.

http://www.zianet.com/NMAMARS/downloads/neets.htm

Wikipedia is another good place to start. It will give you 10 or so pages of introductory material to get you started and then provide a list of web sites that are well focused on the subject. I don't have many technical texts available in English because I live in Taiwan and I regularlly use Wikipedia as a gateway to delve into quite complex electronics and programing topics. It is a good one and will save you from buying books that you may never use.

For active filters, try your library or Wikipedia for a good first text on Op Amps. The extra information [noparse][[/noparse]beside their uses as filters] will open you eyes to a fundamental tool for collecting data from sensors.

For a very basic audio low pass filter using two capacitors and two resistors, take a low at the PBasic text, BasicStamp Syntax and Reference Manual, under FREQOUT. The schematic entitled 'Driving an Audio Amplifier' shows two 1k resistors, one .1uf and one .01uf capacitor that eliminate ALL the high frequency noise from the BasicStamps audio output.

I will let you to figure out the cutoff frequency for this low pass filter. It isn't that hard. You can begin to notice things about a low pass filter [noparse][[/noparse]like the capacitors are going to ground]. Then you can compare it with other kinds: High Pass, Bandpass, Band blocking.

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"Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········

···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Javalin

www.allaboutcircuits.com - look on A/C under "filters"

James