R1 BASIC
A question from the R1BBIT community
Two sensors on one bus, polled every 1000 ms:
CONFIG
ONE_WIRE 4
END_CONFIG
VAR A[2]
DS1820_INIT(A, 1000)
WHILE 1
PRINT "t1=" + A[0] + " t2=" + A[1]
PAUSE 1000
WEND
Every second reading is exactly 85.0. The wire is short and the 4.7k pull-up is in place.
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85 isn't a temperature, it's the register's factory value: the sensor hasn't finished the conversion and you've already read it. At 12 bits that takes up to 750 ms, and with two sensors on a 1000 ms period you don't fit.
Set it to 2000 and it's gone. Thanks! Is there a way to go faster without losing accuracy?
You can poll less often and keep the last value in between — DS1820_INIT writes into the array on its own. Or drop the resolution to 10 bits: 187 ms per sensor, but the step becomes 0.25 °C.
Separately: on a long line add 100 nF across the supply at each sensor. Without it I got 85 even with the right period.