The DPMS Power Strip

   

DPMS (Display Power Management Signaling) is the power management standard for VGA monitors.

With the transition away from CRTs to low power LCD displays, the concept of monitor power management is becoming, well, useless.  However, the idea is a good one, it just needs to be extended to other things.
Here's a fairly simple project that can put ordinary house lamps, TV's, old stereo equipment, etc into DPMS power saving mode.
There are two parts.   The power strip itself, and the the DPMS logic.

Power Strip



The power strip / outlet side is basically a relay controlled by an optically isolated input.   I broke the strip into three sections (normally off,  normally on, and unswitched).
This was done by splicing one side of the AC terminal strip at two points (for two outlets each) and rerouting with some heavy lamp cord.   The live wire was tapped at the unspliced section (but still after the fuse and power switch).   Smaller gauge wires were used for operating the DC power supply transformer, also tapped at the unspliced section.  A total of five wires were brought through (three heavy gauge for the SPDT relay contacts, and two light guage for the transformer).

       

There are no logic components in the power strip itself.   However to operate the relay and transistor, a DC power supply is needed.
(transformer, bridge rectifier, capacitor).  Almost any old wall DC power supply from a toy should work, all that is really required is that it have enough power to switch on the relay, but not too much.  I used loose parts myself,  the unregulated output being about 15v with low current (~100ma).




I built my own optoisolator with an LED, photocell, and some heatshrink tubing,   The best LED color to use is green, yellow, or orange as the photocell is most sensitive to these colors.



LED power input is via a phone jack from an old modem.  Only two of the four connections were used (green and red).

Transistor is a basic NPN, just enough needed to drive a relay coil.

   

Finished, ready to use.




DPMS logic

In my search for a DPMS chip, I stumbled on the Weltrend WT8048.  
This IC does the work sensing whether H/V sync exists and triggers an open collector output when in DPMS suspend or off mode.   With just a few external components, it is easy to control an LED.   For this particular project, I put the chip on a VGA card, avoiding the need for an external power source.




Also for this project, I did not use the standby/suspend mode or mute mode capabilities of the chip, only off mode.  
In this circuit, the LED is on when there is are pulses (normal operation) and switches off when in power saver mode.   The LED output is connected to another phone jack.


       

All that's left now is to plug in and connect the cables.

Result: The DPMS Office


(1.0MB xvid avi)

old stereo, lamp, and tv video monitor - normally on
mood light - normally off
computer, vga monitor - unswitched
pc is diskless, running ubuntu live cd, with two vga cards.

Alternatives

A phototransistor/IR LED combination or an opto-isolator IC can be used in place of the LED-and-photocell.

It's not necessary to use the WT8048.
With some VGA/DVI monitors, you can tap out the LED on the front panel that turns yellow or orange when the monitor goes into power saving mode.   However, if you are switching an old TV,  arcade game monitor, or some custom embedded display, this chip is an easy way to add DPMS support (it also works with a low scanrate).

A more elaborate power control can be made with X10 devices and possibly some protocol hacking.  But you'll have to buy these.

What about DVI?

Power management for digital DVI is not based on DPMS, but rather DMPM (Digital Monitor Power Management).   I haven't been able to find a chip that just does the power management handling, but it is still possible to tap out the front panel LED of an existing monitor.
Fortunately the DVI spec is open (unlike anything VESA produces... $200 for the DPMS spec), so with some work it would be possible to construct a PLD or microcontroller based DMPM device.
Also, on some DVI connectors the VGA analog interface is still present, so a WT8048 will work with these Hsync/Vsync lines.

A Safer Implementation

My unit was based on the cheapest power strips I could find and surplus parts from The Electronic Goldmine, now defunct Olson Electronics (circa 1980), and the trash.
Total cost being less than $20. Of course it could be made safer by using OSHA approved wall recepticals, sealed relay, 12 gauge romex,  additional fuses,  MOVs and snubbers, explosion proof housings, etc.

Links

DPMS Info (that's really about it, not worth spending $200 for the official spec)
DVI Specification
WT8048 Datasheet
Current Sensing Power Strip - Not DPMS capable, but a similar goal.. Uses current from one line to switch on/off others.
Intel and Google's efforts in power reducing devices

Disclaimer

Do not attempt to build one of these unless you fully understand the theory, details, and ramifications of constructing such a device.  You have been warned.

Bryan Chafy
10/30/06