Generic Board design with protection in/outs

[MolsonB]

I'm designing a generic board to use in my cars (or other projects) that the inputs/outputs of the Teensy will be protected.
Just want to make sure I haven't over looked things, or have the resisters on the correct side.

Teensy 3.6
ESP8266 Wifi, CAN, and RS232


Power
Have two power sources incase of failure. Or from different sources (Key ON vs Key ACC)


Analog in
Most of the car sensors are 5V. Using the MCP6404 and voltage divider seems to be the safest way to bring values down to 3.3V


Analog out (PWM)
I read the 74HCT245 is good for PWM speeds. This will drive LED or Servo's.


Digital in
These will just be ground switches. I don't know if I need external pull up or just use the internal instead? Is there an IC chip that can replace this?


Digital out
Some will be able to sink a Relay, while others are just 5V for Led, SPI, etc. 1K resister on the teensy side ok ?



I can attach the whole eagle project file if that helps.

 

[GremlinWrangler]

If getting serious with protection optoisolators can be a simple route. They have speed limits, are digital only and they can end up sinking a bit more current than you might want but do offer true isolation. Is the intended install here into a vehicle with negative or positive chasis?

Ideal is that accidental touch of the car metal work won't have exotic voltages on it.

 

[MolsonB]

I didn't want to get too serious, but I also didn't want a direct pin tied to MCU. Still need to take care when installing / playing around with the board.
Mostly just for projects in my everyday life, sometimes I'll only use a few pins, or maybe all of them in another project.

I think I'm safe to remove the resistors between the teensy and 74HCT IC on Digital out, it's not necessary. Would I need anything on the MOSI output side for protection?

 

[MolsonB]

I see the OctoWS2811 uses 74HCT245 (bus transceiver), but I also looked at the 74HCT541 (buffer) instead. I don't really see much difference between them, other then a nano second here and there in specs.

 

[MolsonB]

Figure I'll use software debouncing rather then hardware. Simplify build time.
Sticking with external pull-up as wire length could be anywhere from 5-10ft.

Digital Input

 

[MolsonB]

Here's my final draft in Eagle. Let me know what you guys think. Schematic only, going to start on board design.

16 - digital out (-)
12 - digital in (-)
14 - analog out pwm
8 - analog in (5v)
2 - serial bus
2 - power inputs
1 - spi out
1 - can bus
1 - wifi