Can anyone suggest an active pullup circuit to replace a typical pullup resistor for an arduino one wire network of ds18b20s? I have 80+ meters of network in a daisy layout of 12 sensors. I've reduced the pullup to 1k, but still having issues with too large a rise time due to capacitance of wire. Read elsewhere that an active pullup could do the job, but no details of a device/circuit. Thanks
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\$\begingroup\$ Define C or rise time to 64% with 1k.. my guess 10nF 10us , what baud rate? Try a 10mA current source, but 1 wire is a big antenna loop. Which is why RS485 is more robust. \$\endgroup\$– D.A.S.Commented Apr 19, 2021 at 18:18
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\$\begingroup\$ But you can’t use parasitic power mode, too much Cpp \$\endgroup\$– D.A.S.Commented Apr 19, 2021 at 18:30
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\$\begingroup\$ What cable you use, what is the capacitance of the cable, and how it is wired (it makes a big difference if it is twisted pair cable and you select the twisted pairs incorrectly)? Do you use parasitic power or bus power? Have you read the 1-Wire Design Guide for help? \$\endgroup\$– JustmeCommented Apr 19, 2021 at 18:35
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\$\begingroup\$ Its just the standard 3 core cable supplied with the sensors. Not twisted or screened. I'm not using parasitic mode, I'll do some tests to find the capacitance. How about a digital optocoupler to each sensor and use a higher voltage down the cable? \$\endgroup\$– The PikeCommented Apr 20, 2021 at 21:53
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One option would be to use an active pull-up device, like the Analog Devices LTC4311.
That said, you'll probably get better results if you subdivide your network into branches to reduce the loading on each.
I would also have some concern about EMI coupling onto a wire run that long. So filtering and ESD protection should also be considered.
answered Apr 19, 2021 at 17:29
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\$\begingroup\$ Thanks for the info, I'll try the LTC4311 first. Failing that I'll split the network, either multiplex (if pos) or use several microcontrollers to read different branches. \$\endgroup\$– The PikeCommented Apr 20, 2021 at 22:03