I sent Dan an Email the other day he makes the Breakout boards which are very good! I asked him if he could make a board with level shifters on! No reply yet but i think this will be a good addition to make use of the SPEED of the 3.6. I interface with Retro 80's chips so need the 5V tolerance on all pins!
@Baggey, thanks for your comments. I have NOT received any emails from you, and always scan over my spam folder too, so don't know what happened there.
I pretty much agree with Paul here. I have thought about those level-shifter chips, but they're expensive [if used on a lot of pins], and would take a lot of pcb real-estate. So I just use the old-fashioned solution ---> resistors. With reference to my new pcb from the other thread,
https://forum.pjrc.com/threads/41277-And-yet-another-Teensy-3-6-breakout-board
1. first, I want to keep my boards roughly UNO-size, because I now have 6 or 7 such pcbs and stack them for my projects.
2. on the output side, 3.3V will trigger most 5V input circuitry.
3. on the input side, as shown I wire series-Rs on every I/O pin, and if I want to i/f to 5V, I can always wire a pull-down R to form a voltage-divider; these will work well, even for fast signals, if the R-values are "low". Eg, 1K series feeding to 1.5K pulldown will give you under 20-nanosec rise-time assuming Zin is 20-pF on the pins [extreme-case high-value]. I figure that's fast enough.
4. people, including me. are always connecting things wrong, so I figure the series-Rs are the single best easy form of protection, that no-one besides me ever uses [except Ruggeduino]. I've never blown up one of my boards.
5. and in fact, I already have 10 pulldowns in those 2 SIP R-networks beneath the Teensy module near the ADC pins, and can wire more in the proto area.
6. I mostly use 3.3V sensors anymore, and for the few 5V sensors I just use the voltage-dividers.
7. for 5V I2C devices, of which I cannot even think of one other than a 5V Arduino chip, I use pullups to 3.3V rather than 5V; this works since the output gates of I2C devices are open-collector [ie, open-drain] pulldown, and use passive pullup-Rs.
Most high-speed chips nowadays, like used here and in raspberry pi and Beagle Bones and Chipkits, are 3.3V anymore, and I think my solution is adequate for what I do. If you're working with 80s style electronics, which is probably all pretty darn slow, then I would just use the T3.5 and would bet its fast enough to do the job.