DS18B20 / Dallas Temperature - unreliable results

[bko]

Hi again @jed

You should read the Dallas/Maxim app note in this earlier posting. In particular I recommend using the resistors shown and something like the FET pull-down in Appendix A. You are asking for a lot of capacitance to be driven by that IO pin.

DS18B20 error "-0.06"

If you are getting all F’s, you are reading the pull-up resistor, not the DS18B20, I think. Are you sure the CRC is correct? Lots of libraries read the CRC but you have to turn on the part where you check the CRC. Some people have had better luck using a 2.2k or 1k pull-up to +5V but you need to use a 5V tolerant pin. There is a Dallas (now Maxim) document that talks about one-wire on long wires and your wires definitely long! They recommend using an active pull-down element (MOSFET) with s…

You may also want to try slowing down the software side to give more time since a few of the pulses in your scope picture are pretty short.

Just for completeness, I think you might want to pick up a Maxim DS18b20 from DigiKey or Mouser, just to be sure you have an authentic part to test with.