Automatic Tracking Dot Disabling in BW Printing Mode - Page 1
Forum section: electronics / projects

author: Cyberdragon
author_rank: Super Contributor
timestamp: December 01, 2015, 08:10:48 pm
content: I read the comments on Dave's recent video and it seems there is a concern of tracking dots not only violating privacy but also just plain wasting toner. Some people are complaining that when printing in high volume the yellow toner runs out when only printing in BW mode. The solution is this: Disable the use of yellow toner when the printer is only supposed to be using black.WARNING: HIGH VOLTAGE WILL BE USED, ATTEMPT ONLY IF YOU ARE CONFIDENT WITH HVThere are many ways of making a circuit to do this but I opted for a simple method that doesn't involve interfering with the digital or PWM signals of the printer. The easiest way I could think of to do this would be to turn off the current that charges the OPC drum for printing. This would involve installing a high voltage relay in the circuit to the charge roller or corona wire to disable it in BW mode.The problem is how to determine when the printer is in BW mode to turn off the relay. It would be hard to determine the actual mode the printer is in from the processor as that will require decoding the digital signals of the printer. The other solution is to keep the yellow normally off and use the assumption that if the other colors are not used then the printer is most likely in BW mode. The fact that yellow is the last color to be printed makes this possible. The circuit would detect if the other colors were used and close the relay to the yellow, probably with an arduino or PIC. There would also be an external override to manually close the relay if you really need to print in only yellow and black.My question is how to detect when the other colors have been used. I was thinking it might be possible to use a current sensor coil around the HV wires to the other colors.

author: JoeN
author_rank: Frequent Contributor
timestamp: December 02, 2015, 01:16:18 am
content: I prefer to send my ransom notes the olde fashioned way...

author: timb
author_rank: Super Contributor
timestamp: December 02, 2015, 08:19:11 am
content: Quote from: JoeN on December 02, 2015, 01:16:18 am"Before I agree to anything, I want proof of life. Show me an LED blinking!" -John Creasy, Man on Wiring

author: tooki
author_rank: Super Contributor
timestamp: December 02, 2015, 10:49:02 am
content: Well, if you're printing so much black and white that your yellow toner is running out just from the dots, you really should be investing in a separate monochrome laser. It'll be faster and cheaper in the long run. (Color lasers are much more sensitive to paper quality than monochrome models, so at high volume, just the paper cost savings are significant.)That said, for color, I've become a total fan of inkjet. They easily exceed the quality of laser (if you're going for quality) and exceed them in speed (if you're going for speed). No, you don't get top speed and top quality in the same model, though. And the consumables cost difference has vanished: high end inkjet sure very cheap to run, and low end lasers are very expensive.

author: tooki
author_rank: Super Contributor
timestamp: December 02, 2015, 10:51:25 am
content: Quote from: JoeN on December 02, 2015, 01:16:18 amHeheheh.Honest question: If you did want to print your ransom note on a color laser, wouldn't it be sufficient to simply write in black on full yellow background? (You know, I'm always looking for new methods and stuff. You never know when you might need to blackmail someone!)

author: Helix70
author_rank: Unknown
timestamp: December 02, 2015, 10:58:10 am
content: Quote from: tooki on December 02, 2015, 10:51:25 amHey, interesting! Now I wonder that too!

author: Cyberdragon
author_rank: Super Contributor
timestamp: December 02, 2015, 07:11:13 pm
content: Quote from: tooki on December 02, 2015, 10:51:25 amWhat if it changes the color of the dots automatically? (experiment anyone?)

author: free_electron
author_rank: Super Contributor
timestamp: December 02, 2015, 08:05:23 pm
content: Quote from: timb on December 02, 2015, 08:19:11 amwe will start snipping pins of the atmega one by one ...

author: tooki
author_rank: Super Contributor
timestamp: December 02, 2015, 09:24:42 pm
content: Quote from: Cyberdragon on December 02, 2015, 07:11:13 pmI've never heard of them using any color other than yellow, because the cyan/magenta/black dots are too conspicuous. But you never know...

author: dexters_lab
author_rank: Unknown
timestamp: December 02, 2015, 11:24:21 pm
content: you could just buy a B&W laser printer for your ransom letters?B&W lasers are cheap as chips and rarely go wrong... just a thought...

author: Berni
author_rank: Super Contributor
timestamp: December 03, 2015, 12:36:40 pm
content: Or use one of those cheep color printers that can only print one color at a time.I got a cheep Konica Minolta color laser printer that works that way. These printers keep the 4 toner colors on a carousel so when printing a color page the printer actually prints 4 times on the drum, changing out the toner cartridge for the next color each time, finally once its done it fuses the ink on to the paper. Obviously this makes the printer 10 times slower for color pages.So in order to make printing in B/W faster they skip the toner switching shenanigans, keeping the black toner cartridge against the drum all the time and fusing the ink to the paper as its being printed to make it get the fast one page every 1 or 2 seconds print speed you expect from a laser printer. In that mode its not capable of putting the yellow dots there because the yellow toner is in the storage carousel.

author: DmitryL
author_rank: Regular Contributor
timestamp: December 03, 2015, 02:26:04 pm
content: Quote from: dexters_lab on December 02, 2015, 11:24:21 pmIf you speak to people who do professional forensic analysis of printed documents, they may tell you that they can also make use of printer's mechanical tract properties to extract information that helps printer<-> document pair identification. Similar to identifying an old mechanical typewriter.

author: JoeN
author_rank: Frequent Contributor
timestamp: December 03, 2015, 11:55:35 pm
content: Quote from: DmitryL on December 03, 2015, 02:26:04 pmMy thinking is you can get a printer for almost nothing at Goodwill for cash. In fact, a new new printer can be had for $25 these days. More power to the forensic guys when dumb criminals screw up, but anyone with a bit of brains would use a "burner" printer. Just sayin'...

author: tooki
author_rank: Super Contributor
timestamp: December 04, 2015, 09:10:06 am
content: Indeed. Heck, I just got a laser printer for free, so I can start doing toner transfer for PCBs. And there were many to choose from. I guess that will come in handy for any blackmailing that may come up. I could even print different parts of the document on different printers, just to add more forensic entropy or something. (That sounds scientific, right?)

author: Gyro
author_rank: Super Contributor
timestamp: December 04, 2015, 10:10:11 am
content: Hell, that's a point - I'm planning to do toner transfer with my Dell color one... I don't want copper dots all over the board!I wonder if there is a hidden command to turn them off?

author: Monkeh
author_rank: Super Contributor
timestamp: December 04, 2015, 10:37:20 am
content: Quote from: Gyro on December 04, 2015, 10:10:11 amI doubt the dots are anywhere near large enough to cause copper to remain. Even if you managed to transfer them, they'd get side etched away.

author: Gyro
author_rank: Super Contributor
timestamp: December 04, 2015, 10:46:16 am
content: Hmm, yes you're probably right. Thanks.I only noticed them the other day when I printed a color alignment test sheet and was looking under a magnifier. I thought it was some kind of 'leak-through' on the yellow toner until I saw this thread!

author: tooki
author_rank: Super Contributor
timestamp: December 04, 2015, 03:09:53 pm
content: Quote from: Gyro on December 04, 2015, 10:10:11 amNo. My understanding is that they're added far, far downstream from the rasterizing process. I read somewhere that they're "added a few nanoseconds before the laser hits the drum". However, it is plausible that printing in pure grayscale mode may disable it. Would be worth a quick test.

author: Gyro
author_rank: Super Contributor
timestamp: December 04, 2015, 05:13:23 pm
content: QuoteThat's a thought, though I suspect that they're always there. It's only when you get a page under bright light with a magnifier that you realise just how many tiny dots there actually are. I'd still be a bit surprised if the manufacturers hadn't slipped in a well hidden defeat command into the printer firmware somewhere just on the off-chance that they get hit by a legal privacy judgement somewhere in the world.