1-Wire in Parasite Power configuration (1-Wire using 2 wires) does not work (again)

[iz8mbw]

Hello. It seems 1-Wire in Parasite Power doesn't work again, reports always 85 degrees.

Some info for you:

root@rpi3:~# uname -a
Linux rpi3 6.1.19-v8+ #1637 SMP PREEMPT Tue Mar 14 11:11:47 GMT 2023 aarch64 GNU/Linux

root@rpi3:~# cat /etc/debian_version
11.6

root@rpi3:~# dtoverlay -l
No overlays loaded
root@rpi3:~#

root@rpi3:~# dmesg | grep -i wire
[    9.279917] Driver for 1-wire Dallas network protocol.
[    9.287128] gpio-4 (onewire@4): enforced open drain please flag it properly in DT/ACPI DSDT/board file
[    9.317419] w1_master_driver w1_bus_master1: Attaching one wire slave 3b.00000014fe14 crc 17

root@rpi3:~# cat /boot/config.txt | grep w1-gpio
dtoverlay=w1-gpio,gpiopin=4,pullup=on

As you can see w1 reports 85 degrees:

root@rpi3:/sys/devices/w1_bus_master1/3b-00000014fe14# cat w1_slave
50 05 ff ff f0 ff ff ff 5c : crc=5c YES
50 05 ff ff f0 ff ff ff 5c t=85000

[iz8mbw]

@popcornmix @pelwell

[iz8mbw]

Just made a test: I changed from 3V3 to 5V the power supply to pin GPIO4 and now 1-Wire works (always using a 4.7khom resistor between GPIO4 and power supply). Well, why now 3V3 is not more enough? Sensors are more precise at 3V3 respect to 5V.

(the cable that connect the 1Wire sensor to Raspberry Pi is only 10 cm long)

[dp111]

I suspect the issue is the host isn't driving the bus high to charge the capacitor at the correct time. This may have worked in the past by luck or the timing just being slightly different.

See https://www.analog.com/media/en/technical-documentation/data-sheets/DS18S20-PAR.pdf Page 3.

On Tue, 21 Mar 2023 at 18:31, Fabio @.***> wrote:

Just made a test: I changed from 3V3 to 5V the power supply to pin GPIO4 and now 1-Wire works (always using a 4.7khom resistor). Well, why now 3V3 is not more enough?

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[iz8mbw]

I don't know if this can the be the motivation. With 3.3 V I'm unable to read sensor temperature but as I wrote the 1-Wire bus can see the chip, can see the serial number and can see the chip resolution but when I interrogate it for temperature it answer with 85000 (85 °C). I'll try to change the resistor from 4.7 kohm to 3.9 kohm and switch back from 5 V to 3.3 V.

[dp111]

Did you see the bit in the link which says the temperature conversion takes extra current and so needs a stronger pull so they recommend that the host drives the bus high to provide the power?

On Wed, 22 Mar 2023, 08:05 Fabio, @.***> wrote:

I don't know if this can the be the motivation. With 3.3 V I'm unable to read sensor temperature but as I wrote the 1-Wire bus can see the chip, can see the serial number and can see the chip resolution but when I interrogate it for temperature it answer with 85000 (85 °C). I'll try to change the resistor from 4.7 kohm to 3.9 kohm and switch back from 5 V to 3.3 V.

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[pelwell]

That's what the w1_gpio driver attempts to do, by forcing the pin to be an output driven high for a while.

[dp111]

That's good. It might be worth checking the timing is correct.

On Wed, 22 Mar 2023 at 13:13, Phil Elwell @.***> wrote:

That's what the w1_gpio driver attempts to do, by forcing the pin to be an output driven high for a while.

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[iz8mbw]

If you need test on new kernel/firmware I can do it.