MT RB750gr3 voltage and temp measurement?

Hardware Questions and Recommendations
1

Hi guys,

I often use this Mikrotik RB750gr3 non-wifi router.
Using stock f/w, this device is able to report its (cpu?) temperature and the voltage of the powersupply.
Does anyone know how to do this with OpenWrt?

I found some attempts on its predecessor RB750r2, which has an ATtiny microcontroller onboard that does this I/O stuff.

But I don't know (yet) if the r3 version also has such a component to be read.

I would be very interested to monitor the supply voltage because I'd like this router to be powered from a backup battery.

Regards - Erik

2

They use a touchscreen controller via SPI.
Not described in OpenWrt DTS. Need to use some quirks to get the upstream driver to work.

1 Like
3

Thank you John,

So this measurement is done by the ZT2046 (placed on board as U902)? Great!
But how to read the figures? I found the package " kmod-input-touchscreen-ads7846"
How to treat it? Should I call it in some way and does it place the results in /proc/... or such?

4

Once you have the ads7846 driver installed and configured (through DTS) then you can read data under /sys/class/hwmon/hwmon*/, or through /sys:
My 760igs, with 12V supply:

find -L /sys/devices/platform/1e000000.palmbus/1e000b00.spi/spi_
master/spi0/spi0.1/ -maxdepth 3 -type f -regex '.*\(temp.*\|.*input\)' -exec bas
ename {} \; -exec cat {} \;
temp1
384
in0_input
278
temp0
38
in1_input
632
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5

Thank you John,

So this isn't simply done by reading some registers I see.
I wasn't familiar with DTS so I have to study that. I just started to set up a new build environment and see if I can build a standard firmware (that won't end op in an error).
Then, I suppose, I will have to add your DTS patch to get the SPI stuff working.

I'll let you know where it ends.

6

Dear John,

I give up on this. After numerous attempts to compile OpenWrt I keep ending up in failures. I tried different versions, different targets and even different build-distro's. Most seen failure was about LLVM.
It looks like compiling is not there for me anymore. Maybe, in half a year or so, when I have te time and courage I'll try again.
For now I just hope that someone will pick this up and add your patch to some release one day.

Thanks for your help