Printer Power Automation

The Dell 1320cn and I keep rumbling along, but one issue I've had for a long time is "other people". Or, to be more specific, other people who need to use the printer.

My concern was twofold; saving power, and not damaging the printer.

Addressing the first concern I added a smart plug to the printer many years ago, with a little Hubitat automation rule which says "turn this off if it uses less than two watts of power for twenty minutes". That works just fine, but it created the second concern. How do I let those other people turn on the printer, but not turn it off before it's had chance to settle?

There's no way I could add a Printer button to HomeKit, as no doubt somebody would turn it on and off accidentally. I thought about adding a feature to the smart plug driver which would prevent being turned off with a delay, but that doesn't help if the delay passes and the printer is still in use. Then, after speaking with the other people, it transpired that even pressing a button to turn on the printer was considered a bit too much effort.

No Buttons

The solution is hubitat-printer-proxy. It's not a great name because it doesn't proxy the printer via Hubitat; but it does rely on Hubitat, and it's the best I could come up with this weekend.

What it does is provide a TCP proxy with buffering between any Mac (see why it's a Mac in the Dell 1320cn article) and the printer. Instead of installing the printer and pointing the client directly at its IP, we now point it to the proxy. It's this proxy that listens for jobs, and when one comes in it triggers the smart plug to turn on via the Maker API, then keeps trying to send the job until the printer has woken up enough to accept it.

Toner

That was all easy enough, but now I was pointing macOS to a proxy I could no longer see toner levels under "Options & Supplies", as it would try to grab those details over SNMP from the proxy IP address, which isn't really the printer.

The solution is to grab and cache that data following each print job and replay it back to the client using snmpd. This way the last toner status information is always visible, regardless of whether the printer itself is powered on or not. Neat!

AirPrint

Those other people then said "why can't I print from my iPhone".

Thankfully, AirPrint Bridge exists, so I didn't need to do much here. We do nothing more than we would with any other printer. Follow their instructions and the job goes via the proxy, turning the printer on in the process. Thank goodness for that.

No Colour

One trick that's worth noting; as the other people are mostly printing things like postage labels, there's no need for them to be doing so in colour. However, CUPS defaults to colour printing, which is rubbish when the label includes half a page of full-colour advert. There are ways to get AirPrint Bridge to advertise the printer as monochrome, but this only affects the print preview, and the job still gets sent and printed in full colour.

Get your printer details from CUPS with:

lpoptions

It'll give you something like this:

copies=1 device-uri=socket://192.168.11.12/ finishings=3 job-cancel-after=10800 job-hold-until=no-hold job-priority=50 job-sheets=none,none marker-change-time=0 number-up=1 printer-commands=none printer-info='Dell 1320cn' printer-is-accepting-jobs=true printer-is-shared=true printer-is-temporary=false printer-location='Media Cupboard' printer-make-and-model='FX DocuPrint C525 A-AP v3.3' printer-state=3 printer-state-change-time=1782681761 printer-state-reasons=none printer-type=37084 printer-uri-supported=ipp://localhost/printers/Dell_1320cn

Grab that name from the end of printer-uri-supported and fire this:

lpoptions -p Dell_1320cn -l | grep -i color

You'll see something like this:

FXColorMode/Output Color: Black *Color

The asterisk shows it's in colour mode by default. Hit it with:

lpadmin -p Dell_1320cn -o FXColorMode=Black

And you're all good:

FXColorMode/Output Color: *Black Color

No more wastage of the colour toner at least.