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About fons

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  1. Hi, I think I will go for the op amp solution (the link you provided is really good, thanks again). I still have a few questions though: Is the ADC range 0 to 5 V or 0 to 3.3 V? What specific op amps would you recommend? I have read that JFET op amps are better suited for high impedance sensors like the Piezos due to their high impedance inputs. The Piezo output signal is bipolar whilst the ADC is unipolar, how can this be solved? For (3) I am considering to replace the ADC by a bipolar one (and while I am at it, I am also considering a Delta Sigma one which should be better suited at this problem). Do you know any pin compatible replacements so that I can simply replace it in the Logic Start Megawing? Do you think it would be possible to use the Papilio/Megawing as power source? What PIN should I use? Would it require the external adapter or would USB be enough?
  2. In case it helps
  3. It is? That's what I initially understood from the schematic on the Megawing spec page but then your book states that Vref is 3.3V . Now I'm confused :S Thanks! Looking forward to it! How could measure it to know for sure?
  4. Hi hamster, First, thanks for your answer (and for your book, it's a really great introduction). Now, getting to the topic itself. Will this low pass filter also ensure that the Vout is always within the expected voltage range of the ADC input? Otherwise, how can this be done? Also, what specific component should I use for the op amp? (maybe this is a stupid question but as I said, I am total newbie when it comes to analog electronics).
  5. Note: this is crossposted from stackexchage , I hope this doesn't go against the forum netiquette (feel free to erase it otherwise) Background Similarly to what Jeri Ellsworth did in her C64 Bass Guitar hack I am working on an audio-to-midi converter for my bass guitar. I am also planning to use piezo discs as sensors placed under each string, connected to a Papilio One, using the ADC of the Logic Start MegaWing (an ADC128S102). The ADC reference voltage is hardwired to 3.3. volts. My problem is that my analog electronics knowledge is pretty bad and I don't have any practical experience (I have given a try to the relevant chapter of the The Data Conversion Handbook but it's a bit too advanced for me). Question What circuit should I use to drive the ADC? The circuit should Implement an anti-aliasing filter. The frequency ranges (excluding harmonics) typically found in each string of a 4-string bass are: E string: E1 (41.20 Hz) to E3 (164.81 Hz) A string: A1 (55.00 Hz) to A3 (220.00 Hz) D string: D2 (73.42 Hz) to D4 (293.66 Hz) G string: G2 (98.00 Hz) to G4 (392.00 Hz) Ensure that the input signal voltage matches the expected range of the ADC (0V to 3.3V as I understand it).I would appreciate as much practical information as possible (e.g. specific circuits and specific parts to use) since, as I have said, I am pretty unexperienced on this. Pointers to books/articles suitable for a newbie like me would also be appreciated.
  6. fons

    ADC in C64 Bass Guitar

    Thanks for the hints Jack. She indeed uses a comparator before passing the signal in to the FPGA, I just didn't know the reason for it
  7. fons

    ADC in C64 Bass Guitar

    Hi, I saw this video from Jeri Ellsworth, in which she creates a bass guitar synth using a Papilio One to do the real-time string frequency analysis. I would like to know how she does the ADC conversion. I am new to FPGA's but AFAIK the Spartan 3E doesn't accept analog inputs. Am I right? Do you think she is using an ADC wing? In the video, it looks like look like she is plugin in the 4 analog inputs directly to the FPGA though, see