• UPSMon

Status: This is an active project. For near-realtime progress logs, please have a look at the ProjectsBlog.

Circuit description

I use an uninterruptible power supply (UPS) named "PowerSure 600" made by Liebert to secure electricity for my home server computer. However, in case a power outage lasts longer than the UPS can provide energy (from two serially connected 12V 7Ah lead batteries), I want the system to shut down cleanly. Ideally, it would also switch to some power saving mode (e.g. clock down the CPU) as soon as the UPS kicks in.

This requires the UPS to tell the computer about its state. For this purpose, it has a DB25 connector on which two status signals can be obtained, and through which the UPS can be shut down remotely. I want to build an interface between this DB25 port and the USB of the server system.

I am using the ATtiny2313 microcontroller and a FT232 USB-to-UART interface to get one talk to the other. The interface is capable of relaying UPS state (power good, on battery, battery low) to the host computer, and can issue a shutdown command to the UPS if commanded so by the host.

Revisions

YA-B04.01

External interfaces

Protocol description

Communication through the USB serial interface uses 9600 baud, 8 data bits, no parity, 1 stop bit ("9600 8N1").

Host to UPSmon

The following commands are supported from host to UPSmon:

i

tbd

v

tbd

t<nn>

tbd

FUSEFUSE

tbd

FUSECNCL

tbd

.

tbd

UPSmon to Host

The following messages are sent from UPSMon to host:

PWR_FAIL

The UPS reported that external power is no longer present, after it was okay

PWR_GOOD

The UPS reported that external power is present again, after it was gone

BATT_LOW

The UPS has asserted a signal reporting low battery power

BATT_OKY

The UPS reports its battery in a good state, after it was BATT_LOW

ACK_FUSE

UPSMon acknowledgment of the FUSEFUSE command

NAK_FUSE

UPSMon received a FUSEFUSE command but does not execute it, probably because external power is PWR_GOOD

CNL_FUSE

UPSMon acknowledgment of the FUSECNCL command

NAK_UNKNOWN

UPSMon received an unknown or unsupported command through the USB serial interface

Files

• Schematic

• Etch mask

• Part placement

• Firmware rev 02

• Host-side control daemon currently under development.

CategoryElectronics

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