[sixtharmy]

Hi Xaq, Great little site. I hadn't seen this before. I'm not terribly interested in HP inkjets (for a number of reasons that I'll probably get into sometime), but there is so much overlap among different designs that I'm sure I'll discover something interesting. Thanks again.

I read a while back that a digruntled ex-employee, or engineer, or designer, or consultant for HP revealed that they used an uncommon, but available, assembly language in the firmware of their printers. As a result it is possible, though far from easy, to reprogram their firmware. I suspect that this is true, because about 6 months ago some people at Clemson who are using HP inkjets to produce artificial bio membranes reported in a paper that they were using HP printers with altered firmware. This may be a way to approach the inkjet control problem. We'll have to see.

This brings up another point. Manufacturers go to great lenghts to keep other manufacturers (and us) from finding new ways to use their equipment from which they can't earn a buck. They all use the Gillette marketing strategy of "give them the razor , but sell them the blades" in terms of printers and ink. So, they engineer in all sorts of ways to keep you buying only their ink. If you don't even use ink, then they earn nothing. In fact, they sell the printers so cheaply that they might actually lose money.

To give an example of how far they go to protect their technology consider the following. The Epson Stylus Color 740, Stylus Photo 750 and Stylus Photo 1200 all use the same controller board, though presumably with slightly different firmware. This board comes in a Rev. A (used briefly) and a Rev. B form. In the Rev. A the bipolar stepper motor used to advance the paper is controlled by a pair of 16 pin Allegro 3955 chips. In the Rev. B the same function is preformed by a pair of 24 pin Allegro 3957 chips. Allegro publishes a great deal of information about the 3955 (good site about stepper control!). They don't even list the 3957. As far as I've been able to determine, the 3957 is a 3955 with eight extra legs that electonically do absolutely nothing. In fact, I doubt that they're even connected to the IC's microcircuitry. They do, however, alter the order of the functional pins from the pin-outs of a 3955. As a result, it's necessary to take a scope to the operating chip to find out what's what. Epson payed Allegro to manufacture their 3955 silicon in a slightly different plastic package just to make reverse engineering their controllers a tiny bit more difficult. This is only one of the booby traps I've discovered while examining their hardware. Its another reason that I suggest building a controller from scratch, rather than trying to use anything but the absolute minimum of manufacturer hardware. If I have so more time I'll bore you all again later today. If not tomorrow.