2n2222 transistor logic shifter not working

Are you sure you've got them connected the right way?, I'm somewhat confused by your labelling rx and tx.

But for 5V down to 3.3V you just need two resistors as a simple resistive attenuator, no need for a transistor - so you don't need the lower circuit.

For the top circuit, the emitter of the transistor connects to TX out from the 3.3V UART, and the collector connects to RX in on the 5V UART.

You might have a look here:

I use the MOSFET converter from Nigel's link, works fine.

ok I appear to have it working in one direction. The pi can send data to uno.
However for some reason the pi appears to not see the reply back from uno.

I am using the two resistors method to step down the logic level.
but for some reason it appears to not see the signal.
When I probe the middle of the voltage divder, the voltage switches betwen logic high and logic low as expected.
But the pi doesn't see it.

I have checked for continuity between the rx pin on the raspberry pi to the voltage divider. Its fine.

confused!

amateur_24 said:

But the pi doesn't see it.

Click to expand...

Hi amateur. It's been ~1 month since your last post. Have you got things working yet?
If not, have you double-checked that the Pi pin is configured as an input and that the Pi and Uno have a common ground connection?

This is all over the net as a bi-directional converter, but I am suspicious when
you add up all the tolerances (especially 2N7000 worst case Vt) its logic level
noise margin pitiful, and possibly non functional :



I think this better choice :





Regards, Dana.