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Jul 18, 2012 at 12:15 comment added Brad Robinson @stevenh, Ah OK I think I understand that. Updated the schematic to reflect it.
Jul 18, 2012 at 9:47 comment added stevenvh @Brad - Updated my answer. Apart from R1 (I mention it in the answer) it looks OK. You're doing fine.
Jul 18, 2012 at 9:39 history edited stevenvh CC BY-SA 3.0
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Jul 18, 2012 at 9:18 comment added Brad Robinson @stevenvh kHz=typo. I've updated the question with a new circuit diagram based on your comments and my understanding of what you've described. Am I on the right track?
Jul 18, 2012 at 7:35 comment added stevenvh @Brad - kHz! not Hz. Cutoff frequency = 1/(2 pi RC), where R is the parallel of R23 and R24 (this answer explains why). So f = 1/(2 pi 1.3k\$\Omega\$ 10nF) = 12.2kHz. This is a suitable comparator. You'll have to add a 10k pull-up resistor to its output.
Jul 18, 2012 at 2:48 comment added Brad Robinson Also, you're right, the Microbee had line-level output, not mic level. Which makes me curious - how could you modify that to work at microphone level (I'm thinking of sending this to an iPhone for recording).
Jul 18, 2012 at 2:47 comment added Brad Robinson @stevenvh Thanks for detailed response, though some of what you say goes over my head. I have limited electronics knowledge, but trying to grow it so I've just been reading up on RC circuits, op-amps and comparators. I should probably post these as separate questions, but: 1) how did you come up with 12Hz, and 2) could you recommend a comparator? I'm actually hoping to drive this off the 3.3V available on the PMod if possible.
Jul 17, 2012 at 16:44 history edited stevenvh CC BY-SA 3.0
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Jul 17, 2012 at 16:23 comment added stevenvh @Kellen - Oh dear. Yes, you're right, especially if you think of decoupling power supply lines. Here I was thinking of decoupling the DC from the signal :-).
Jul 17, 2012 at 16:14 comment added Kellenjb "Decoupling normally means removing DC content of your signal by means of a series capacitor" - isn't a series cap a coupling capacitor? A Decoupling cap removes the AC content.
Jul 17, 2012 at 15:53 history answered stevenvh CC BY-SA 3.0