SDI-12 Communication - 3.3V Microcontroller Level Shifted Up To 5.0V For Data

Dave Lowther

Joined Sep 8, 2016
224
I built one a while ago. In my case I wanted to level shift between 9V and 3.3V, but the same circuit would work for 5V. I wanted to convince myself of how it worked because at the time it was the first time I'd used a MOSFET. The notes I made are attached.
 

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Ian0

Joined Aug 7, 2020
9,667
Have you checked if your micro has 5V tolerant inputs?
What is the logic high threshold for the bus? Is it 2.4V?
If, the answer to both is “yes“ then they are compatible without any need to make an interface.
 

MrAl

Joined Jun 17, 2014
11,389
Excellent documentation, Dave. Nice work.
Yes @Dave Lowther very good work and very good illustrations. That's probably the clearest i've ever seen on this type of device.
This shows that although the MOSFET turns on at about 2.0 volts (at some temperature) it has to be able to turn on at about 2.5 volts to be effective in this circuit, or at least as effective as it should be. The diode in that direction may or may not be sufficient.
 
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