Teensy 3.5 interfaced to a RAMPS1.4 board

[Jasoroony]

Hi all,

I'm using one of these bi-directional logic level converters to interface a Teensy 3.5 with the MOSFETs on a RAMPS (originally D8, D9 and D10 on the mega2560): https://www.sparkfun.com/products/12009

Everything works really well once my sketch gets going / the pins are configured, however, when I first power-up or reset the Teensy all 3 MOSFETs turn on briefly until the sketch starts. This is obviously not at all desirable, so I've tried using 10K pull-down resistors on the low voltage side logic pins leading from the Teensy, but it made no difference.

I was considering trying pull-down resistors on the high-voltage side logic pins leading to the MOSFETs, but I thought that might make the "bi-directional" properties of this converter board stop working... So I figured I'd ask here for opinions.

The RAMPS board is being powered with +3.3v for +3.3v and +5v and everything else works as expected (when I get closer to finishing, I'll be running an LCD of its own +5v supply) with the steppers moving smoothly and fast so I'm pretty happy with the way it's working except for this one issue.

Any help appreciated,
Jason.

[PaulStoffregen]

The logic level convert is based on pullup resistors, so it's always going to have this problem.

You should use this, with a weak pulldown on the Teensy side.

https://www.adafruit.com/products/1787

[Jasoroony]

Thanks for the quick answer Paul, that's great. I can also see they are available in Australia too, so even better.