crazydoc
Well-known member
I have built an optical microphone that is so noisy as to be useless. It uses a reflective optocoupler with an IR LED and a phototransistor in the same package. I am attributing the noise to the phototransistor (possibly erroneously) and am looking for configurations to make it quieter.
The basic circuit is the common emitter as in (a).
With respect to noise I expect (b) is equivalent.
Does anyone know, or care to make a guess if any of the other circuits or those that follow in the next image would be any quieter, or have any suggestions of other circuits that might work?
Unfortunately, there is no base connection to apply any feedback to, unless it were optical feedback.
I am using a Vcc of 5 volts - would increasing this (to a max of 30v) have any effect on the noise?
Would changing the value of the load resistor make any difference - in other words, would increasing or decreasing the current through the transistor make a difference?
Thanks for any thoughts you might have - I'm trying to get an idea of what might work without having to build all the circuits. Of course, it may be that using a phototransistor in the design just ain't gonna work and I'm screwed from the get-go.
The basic circuit is the common emitter as in (a).
With respect to noise I expect (b) is equivalent.
Does anyone know, or care to make a guess if any of the other circuits or those that follow in the next image would be any quieter, or have any suggestions of other circuits that might work?
Unfortunately, there is no base connection to apply any feedback to, unless it were optical feedback.
I am using a Vcc of 5 volts - would increasing this (to a max of 30v) have any effect on the noise?
Would changing the value of the load resistor make any difference - in other words, would increasing or decreasing the current through the transistor make a difference?
Thanks for any thoughts you might have - I'm trying to get an idea of what might work without having to build all the circuits. Of course, it may be that using a phototransistor in the design just ain't gonna work and I'm screwed from the get-go.