next topic »

[Reply #45 on:]

I tried searching for the TI-07X but search turned up nothing on Mowser with that??????

My Bad, it's TL-07X by TI and X as in several packages:

http://focus.ti.com/lit/ds/symlink/tl072.pdf

Lefty

[Reply #46 on:]

koyaanisqatsi:

How did the breadboard playing turn out?????

I got this far:   ;D



But I did work on my current Arduino project (alternator-driven LED bike headlight).  So it was a good weekend.  I will be playing around with this soon because said project needs a good PWM to analog conversion as most LED drivers don't take 4-8KHz PWM inputs and 490 Hz is WAY too slow when you're traveling at over 30MPH.  It's pretty psychedelic, actually.    :o

It just occurred to me that the RC filter could use smaller parts if you use the TCCR stuff http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1235060559/4#4 to bump up the frequency on the PWM output.  If it were at one of the really high freqs like 31KHz, you could use a lower value cap and the output ripple would be smaller.

[Reply #47 on:]

vancouver reefer: that is exactly what you need. Also follow koyaanisqatsi's link to modify your PWM freq and you should have a  pretty good modulator on your hands/

[Reply #48 on:]

Check out this MAX280. Its a 5th order Low Pass Filter IC:
http://datasheets.maxim-ic.com/en/ds/MAX280-MXL1062.pdf

That in combination with an op amp for gain should make your life easier.

Look at Figure 6 on Page 7. that should be exactly what you need. It eliminates the need for multiple caps and resistors if you want a higher order filter, which you might need, depending on the results you get.

[Reply #49 on:]

This is a switched capacitor filter. I have not used these recently but I have had trouble keeping the clock frequency out of the output. For audio applications I got a noise even when the clock was above the audible range. The clock you feed into it defines the cut off frequency. This has an internal oscillator and you provide the R & C.
 
With a bit of luck they are better nowadays.  

[Reply #50 on:]

Wouldn't the R and C provided only add the last order? i.e. the first 4 orders are in built into the filter? the data sheet shows the examples as pretty clean. was the cut off requency decided by the duty cycle or frequency of the clock?

Once again, Grumpy please write an advanced tutorial on op amps!