DS18S20 power on H/T/S board

[TimCole]

Greetings Eric,
If I've got the current schematic for the Humidity/Temp/Solar board, it looks as if the Vdd pin on the DS18S20 is tied to ground. But tying the Vdd pin to the +5 line on board would eliminate the need for a strong pullup cycle while sensing the temperature.

Is there any reason why that *shouldn't* be done? I haven't assembled the board yet, and I'm considering tying the DS18S20's Vdd pin to +5V when I finally get up the nerve to assemble the board. (Yes, I'm cringing at hand SMD soldering. The ICs are okay, but those teeny little capacitors --- I have enough trouble seeing them, let alone soldering them! :unsure: )

Cheers, Tim

 

[ericvic]

Tim,

Those tiny parts aren't too bad. Helps if you have some sort of magnification and a small iron tip.

You could definitely hook VDD of the DS18S20 to +5v. The reason the board is not designed that way is because you don't have to supply external power to the board and if there is no external power then the VDD pin must be connected to ground. Since we noticed that many people use parasitic power we decided to just go ahead and connect VDD to ground. Also most commercial 1-Wire software out there does a strong pullup on a temperature read so it wouldn't have made any difference in speed.

Eric

 

[TimCole]

Since we noticed that many people use parasitic power we decided to just go ahead and connect VDD to ground.

That's what I thought, but I wanted to make sure I wasn't missing a point. It's great to be able to ask what the designer had in mind. Thanks for the quick answer.

Cheers,
Tim Cole
Ottawa ON