Babich said:
We made the temperature sensor with DS1621 and we have problem reading
temperature. It always displays temperature of -60 C (-76 F). (both of
them). We used following shematic
http://www.electronics-lab.com/projects/pc/010/
Please help us!!!
Sorry on my bad english
First of all, I've never used that DalSemi device. I have used only the
DS1820, but I've used it extensively. I've never read a DalSemi via COM
port, only with uCs. Nevertheless, some of what I write here might be
"all wet".
Your project uses a Win PC and COM port to read the DalSemi device(s).
There might be timing problems injected by Win. I know that DalSemi
1-wire devices have strict timing requirements. Have you scoped the COM
port and compared traces to sensor timing specs.? (I admit I don't know
that the device you're using is 1-wire; maybe it uses Data and Clock
lines. It's been a while since I read up on DalSemi temp. sensors.)
The temp. you're getting is (as I recall) the max. negative temp. that
the device can report, which corresponds to a large negative number.
Perhaps your sensor(s) are not responding at all. THe PC might simply
be reading a line that is normally high and never gets pulled low. Or
a device could be responding OK but the PC reads one or more bits too
early/late (Win timing problem). Or, if you're using addressing, that
address could be corrupted due to PC's incorrect timing.
Or ... all of your sensors are defective. This isn't such a far-fetched
idea; I once got three inoperative DS1820 from a distributer and found -
with DalSemi's tech. support - that *all* devices were defective.
I would go bug the guy who wrote the VBASIC code and ask for his help.