R2 in Dana's circuit is not required with the TIP Darlingtons.

That circuit is not a "buffer." It is an inverting level shifter/driver. If you can't tolerate the inversion you either need another inverter or you can use a common-base level shifter (emitter of NPN shifter to Arduino output, base to +5V through 5-10k (typically), collector to base of TIP). Common base shifters are often overlooked but can be very useful.

 

The Arduino can be configed to be open drain, but there still is a parasitic diode
at the pin such that the pin V can never exceed Vdd + Vdiode, or for 5V Vdd ~ 5.7V
So you will never get the PNP shutoff this way. As O-Bee-Wan-549 points out.

This is basically the way -

View attachment 160626


Regards, Dana.

Thanks Dana!

I’m trying to understand your example. You have a 2N3904 driving a 2N3906. I’ll be driving a TIP42C and s TIP120. Does this affect the circuit?

Secondly, I had base resistors of 240/330 ohms on the TIPs. Your resistors are significantly higher. My calculations come nowhere your values.

Thirdly, when ‘chaining’ resistors, how do you calculate their values?