Quote Originally Posted by Acetronics View Post
Hi, Ioannis

I just wrote a 255 values lookup table ( convert a LOG pot to lin response ) ...
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I use a small old Casio FX-880P personnal Computer ... programmed in BASIC ... WOW !!!
Alain
Hmm, a log pot to table? Interesting idea!

I have such a Casio too (the PB-410 model). It helped a lot in the past!

Quote Originally Posted by Darrel Taylor View Post
Ioannis,

Interesting problem.
I looked at the emesys site, and the idea of using NCD/DCD for the log function is really interesting (and I think, workable).
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Are those voltages what the PIC is seeing? -40db = 20mv etc.
Or is that before an RMS-DC conversion?
And if not, what does the PIC see?
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Thanks Darrel. No, I am not in a hurry. I am trying to make it as fast as possible in response. The program is doing other things too so cannot affort delays in tables to choose one of 60.

Yes the NCD/DCD is clever idea. Trying to comprehand...

The 0db as seen on most old cassete recorder is the standard audio level of 1mW at 600ohm. That is about 0,775V rms. If a real VU-meter is checked, the dynamic range is more than 40db. On good ones, it extends even more. So, a log scaling has to be utilized, in order to make good use of the LCDBargraph. Just ADC and displaying makes for nearly 16-19db range!

The -40db is 7.75mV rms or 22mVp-p. These voltages have to scaled and converted with rms converter or active rectifier. Max range would be +6dbm. That is 1.55Vrms or 4.36Vp-p.

I intend to scale the 1.55Vrms to 4Vdc max (or somthing near) for the PIC to be happy.

Ioannis