i'm triing to build a musical instrument using piezos as knock sensors and arduino bluetooth
it has to be very sensitive as i dont hit piezos directly (but on wood they are stuck onto)
it is working well on duemilanove with threshold = 1 (/1024)
but when trying same code with bluetooth one i have a lot of continuous values from 0 to 8
i tried to plug piezo circuit on mic input to hear the problem and here it is :
a guy just told me an electret microphone needs power to work
Yes but that amplifier is providing power to the mocrophone through the 10K resistor.
use the same circuit with a piezo but don't fit R1.
Anyway are you sure that hum pickup is real? It just looks like a measurement problems or grounding problems rather than anything the BT contributes. You have got a common ground between the ardiono and the BT module?
i did some over tests with my microphone input today and i m not sure anymore this is due to a buzz as i don't see it anymore
anyway
when pluging 1M[ch937] resistor on arduino bt between ground and any analog input, arduino still send continuously values from 1 to 8 for this input
i don't know why but i guess i can't resolve this problem as i'm not into electronical stuffs enough to get into arduino
so i think my only choice if i want to keep it wireless is to preamp piezos (with my 4.5v battery pack)
are you sure about what you said for this preamp sheme
(sorry to ask but i got to be sure as i dont own components yet)
removing the whole r1 part will do the trick ?
when pluging 1M[ch937] resistor on arduino bt between ground and any analog input, arduino still send continuously values from 1 to 8 for this input
Yes I wouldn't expect a 1M resistor to ground to have any effect on the input. You could try connecting a 0.1uF capacitor across the resistor to hold the peak charge a bit longer.
are you sure about what you said for this preamp sheme
I am sure it is a preamp schematic, I am not sure it will solve your problem. It is a simple self biasing common emitter amplifier and with no feedback the gain will be the gain of the transistor. The data sheet says the gain should be between 100 and 300 so that is what you will get. Whether this is enough is an other matter.
No that will not work. You have isolated the transistors base and you will get no biasing current down it.
The gain is X100, so with a reading of 8 you might get a reading of 800.
If you want to cut it down do it on the input of the arduino with a potential divider coming fro the transistor's collector, don't mess with the front end.
If you want to cut it down do it on the input of the arduino with a potential divider coming fro the transistor's collector, don't mess with the front end.
sorry i don't know much in electronic this is my first circuit building
do you mean that to get a lower gain i should add a resistor near c2 ?
It can't get get bigger than 5V because that is what the transistor is being fed with. So any larger output will simply just clip at 5V.
Now you will have no trouble with this because of the 100K series resistor, but when you have a capacitor coupled signal with one side of the capacitor going from 0 to 5V the other end of the capacitor can go from 5V to -5V. The 100K resistor will protect the arduino input but you might want to add some catcher diodes to the top and bottom rails, like here:- http://www.thebox.myzen.co.uk/Tutorial/Protection.html