[Nut-upsuser] 24V DC ATX PSU with limited UPS functionality over USB

[Charles Lepple]

On Thu, Mar 13, 2008 at 5:50 PM, Jean Delvare <khali at linux-fr.org> wrote:
> Hi Michelle,
>
>
>  On Tue, 11 Mar 2008 16:22:09 +0100, Michelle Konzack wrote:
>  > Hello Developers and *,
>  >
>  > I am working on a "24V DC ATX PSU" for Photopholtaik Systems which can
>  > have input voltages from 18V to 27.7 Volt and is entirely modular,
>  > which mean, you can select the desired module/s (up to 6) from ATX
>  > (96/144/240/300W), P4 (144W), SATA (82/305W) and Device (34/68/136W)
>  >
>  > And last not least, I want to build a "PowerWhatch" module which should
>  > be connected from the PSU to an internal USB port of the mainboard.
>  >
>  > Currently I do not know, whether I should use Maxims 1-Wire chips like
>  > the DS2450 which has four AD-Converter or a I²C/SMBus solution.  Both
>  > will work with the DS80C411 Microcontroller...
>  >
>  > Now the question to you:
>  >
>  > Since I do not want to reinvent the wheel, I like to use existing
>  > programs where I think, NUT is the perfect solution...  The problem is,
>  > HOW I have to deliver the data to it or how must I provide it?
>  >
>  > The "PowerWhatch" module picks only the Voltage and Amperes and
>  > Temperature from each of the 11 modules... and maybe it will store them
>  > for a while in a 8-16 kByte NV-RAM or something like this...
>  >
>  > If you have ideas or suggestions, please let me know.
>
>  Given that you are working on a PSU and not a UPS,

I guess it depends on which part of the "limited UPS functionality"
Michelle is referring to.

If the PSU signals to the PC that it is time to shut down due to lack
of reserve power, then it might benefit from NUT's existing
infrastructure (granted, the "N" in NUT is often extra baggage...)

> I am not sure that
>  nut is the best tool to interface with. Wouldn't it make more sense to
>  add one or more hardware monitoring chips in your PSU and connect them
>  to the motherboard's SMBus, and use a hardware monitoring driver in the
>  kernel to monitor all the values you are interested in? There are many
>  popular chips already supported by the Linux kernel, which can monitor
>  several voltages, temperatures and/or fans. And then there's a library
>  for applications to access the data easily.

If you have a specific motherboard in mind, this is probably a good
plan, but not all motherboards with I2C make the bus available to
external devices.

Another advantage of going the HID PDC route (regardless of whether
NUT is involved) is that the device is essentially self-describing. If
the first version does not have a shutdown flag, but later versions
do, then very little driver code needs to change - just device
firmware.

Also, I believe that GNOME has a power monitor that works with HID PDC
devices out-of-the-box, which would be another bonus feature if you go
down the USB route.

-- 
- Charles Lepple