Talk:RPi GPIO Interface Circuits
Simple Diode Level converter --> Is the schematic backwards?
I kinda think has RxD & TxD transposed. The RxD on the ATMega should RECIEVE 3.3v OK, but, the RxD on the Raspberry pi needs the voltage drop from the diode.
Can someone confirm this? I'm a master of transposing these and making the same mistake myself, but... I'd appreciate the eyeballs. If someone can confirm what I see, I'll happily fix the file.
No, that's the way round I've got it. The diode is shifting the 0 and 3.3v from the Pi to ~0.7v and 4.0v at the ATMega's input pin. The data sheet gives the ATMega's VIH as 0.6Vcc, which is 3.0V when running from a 5V supply. This ought to 'just about work' but I found it was unreliable; possibly my wiring arrangements were rather noisy and the supply voltage was on the high side. Anyway, the diode shifter fixed it 100% for me.