24VDC inputs

[rmoertl]

First time posting.  Tried to review the other Prop-1 posts for this, but didn't see what I'm looking for:
I'm used to using industrial PLC's with higher voltage sensors (inductive, capacitive, optical, etc).
If I need to connect a 24VDC industrial sensor to an input on the Prop-1 (or Prop-2), do I need a resistor in series?  Or can I connect directly to the input pin(s)?  Is there a limit to how many 24VDC sensors I can connect?  Any help is much appreciated, thanks!

[JonnyMac]

Do not connect 24VDC directly to the TTL inputs -- you will definitely "let out the blue smoke."

The easiest interface is probably a simple a divider.  The values shown will knock the voltage down to a a safe level.  Another option is to replace the 4.7K with a 5.1v zener diode.

[rmoertl]

Perfect!  Thank you so much Jon!  Any suggestions on wattage for resistors?  1/2 or 1/4?

[JonnyMac]

The wattage works out to 0.019 so 1/4 resistors will do the trick. 1/2w is fine, too.