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Topic: Problem with using a PN2222 Transistor as a switch for a CSR8645 Bluetooth board (Read 970 times) previous topic - next topic


Because the pins have to be pulled high the opto would ideally have to have an PNP transistor in them which is not normal. Yes it might be possible to use an NPN in emitter follower mode, but it might not switch high enough.

An optocoupler usually has an NPN transistor, but because the base is not connected, whether PNP or NPN is irrelevant - it is not an emitter follower.

But an interesting matter to research  :smiley-eek:  as it may impact on the saturation voltage.

You can get opto-couplers in quad packs.


Yes it is relevant if it is a PNP or NPN because of the saturation voltage and the charge transfer.

OP - you need to look at these signals with an oscilloscope to see what you have got. At the moment we can not supply a working solution only what might work.


ok i hooked it up to the oscilloscope and measured both COM to GND and Play to GND i will upload the pictures of the results in 4 different post due to the max upload size.

Thanks to all of you for your effort.
If you need me to do more measurements i try to do them asap.


Maybe COM is the more positive point, put your black meter probe on COM, red on PLAY, what is the voltage AND polarity?


Maybe COM is the more positive point, put your black meter probe on COM, red on PLAY, what is the voltage AND polarity?
Yes, COM is the one with a higher potential i am reading about -1.8V if i connect red to PLAY and black to COM.


What voltage are these signals, it is hard to see from the oscilloscope traces?


i dont really know how to measure that properly, but i have tried to compare the DC offset of two ports to each other and came to the conclusion, that the offset between the COM and PLY is just under 1.8V while the DC offset of the other ports to COM is slightly under 1V.
Furthermore i have looked at the Peak to Peak Voltage of these Signas which didn't seem that consistent while measuring. But all of them jumped around between 1V and 0.8V

I hope that is the measurement you need  :)

In addition, the tranistors set i ordered arrived today.
It contains the folowing PNP Transistors:


I hope at least one of them is fitting for the solution you've provided in the past days


i dont really know how to measure that properly,
Just say what the volts / cm was set to on the oscilloscope when you took the measurements.


The voltage per square is marked at the bootom left corner. It was 100mV for the compared picture and 50mV for the individual picture.



Are you sure that you are not using a X10 probe?
No, i used a X1 Probe and the oscilloscope was set to the same. I will measure it again when i come home. Maybe the picture i've sent you is way to far zoomed in and the amplitude of the signal is higher than it looks like.


Hi again,
i've just hooked it up to the oscilloscope.
I added a display for the avg Voltage  and for the Peak to Peak Voltage for both signals at the bottom of the picture.
In this picture yellow is the signal of COM and blue is PLY


I've made a mistake with the last picture, the signals where shifted in y-direction and i said that yellow is COM, which is totally wrong.

In the attachment is a new picture with non shifted signals. Again wit Vavg and Vpp for both signals and this time yellow is COM ;)

Sorry for the confusion i might have caused

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