Alright I'm designing an effect and I need the micro to know when someone plays a note. So I thought It'd be simple right. Rectify the input and use A/D to read when a note it played. So this is what I came up with.
(http://img140.imageshack.us/img140/3676/rectifying.jpg)
(from the Output, the top of the cap C5.)
But in reality what I get is something like that - but it's very frequency dependent. For any frequency above about 100Hz it gets attenuated a lot (like below 100mV for 1kHz!) but when I sim it in spice with those cap/res values it works perfectly in the range 80-5kHz?? Also what's odd is if I remove the discharge resistor (R13) I get 0V on the output, shouldn't I get ~4V as that cap can't discharge.. I've double and triple checked everything.. tried a million different cap/res values. Looked on a scope it looks good until after D1. Everthing is connected as it should be, there just must be some theory I'm not quite understanding?? Any ideas would be appreciated!
Look at the datasheet for your uC, often the A/D converters have a relatively low input impedance, like only a couple of kiloohms. You may need to put a buffer after that capacitor before it goes to your microcontroller.
Also, if your microcontroller has a analog comparator input that may work better in this application.
Quote from: Seljer on April 21, 2012, 06:37:06 AM
Look at the datasheet for your uC, often the A/D converters have a relatively low input impedance, like only a couple of kiloohms. You may need to put a buffer after that capacitor before it goes to your microcontroller.
Also, if your microcontroller has a analog comparator input that may work better in this application.
I thought that could be the case too, but with the micro removed it's still the same. It's really odd. Something strange is going on.. I might try a buffer but it's a big pain to do.. as it's on a PCB. It works as is but it's frequency response is bad, it will detect low frequencies okay but not so much the higher notes.