There are of course various optical components in the sanner assemhly. A pair of cylindrical lenses IIRC, various mirrosm and some kind of optical uinit on the front of the laser diode. Setting up a (CX engine) scanner from scratch was 'fun' too :-). It's an IR laser so you can;'t see the beam. I was tracing it through the optical bits with an IR remote control tester :-). The origian laser controller was on/off only (but not a simple design due to the speed reuired). There was a DAC (IIRC discrete resistors in the SX engine) to steh laser diode current, but that was done AFAIK once per page (it depended on the sensitivity of the drum in the toner cartridge, encoded by a couple of plastic clips on the cartridge detected by microswitches on the side of the PSU module). Would uofficial scheamtics of the SX engine be any use? When I've recovered from the 'treatment' at the local quackshop and when the temperature has dropped enoguh to be conducive to hacking, I will see what I can dig out if you are interested. Not AFAIK (or at least the CX enginer controllers I've worked on don't). The motor speed is controlled by a PLL-tpye thing (the chip on the motor PCB in the scanner unit, with an 'FG' coil on the PCB). Any slight errors in the bir rate would slightly cheange the size of the printout, but who actually checks that (rememebr a crystal almost certainly better than 1 part in 1000, so the erors will not be large). The CX and SX printer engine interefaces are remarkably similar (to the extend that the CX-VDO simply has a cable from the external DC37 connector to the 34 pin header on the DC controller board, the SX does have an extra PCB, but it's just logic buffer chips). I should ahve scheamtics for that board (and the CX engine) too. I think the PERQ scheamtics books are on bitsavers. Take a look at the OIO board schematics, you should find a CX-VDO printer interface there. Agian I shouldbe able to provide details of the state machine ROMs, etc. -tony

Yes, Most semiconductior sensors, such as CCDs, respond to near-IR. I am told you can 'see' most remote cotnrol outputs using one, for examplke. Quite likely. The problem is that it was _me_ who was setting up this CX laser scanner module, and I am sure you know by now the sort of cameras I have :-) -tony

I;ve not looked for it for some years.. Err, yes... But if I am setting up the optics in a laser printer scanner, I want to be able to dtect where the beam is (roughly) going and then tweak the lenses/mirrors to get it where I want it. Not take a photo, process the bit of film and then tweak the scanner optics, take another photo, etc. I assume if you use a digital camera for this, you observe the results on the built-in LCD monitor of the digital camera, you don't take picutres, upload them to a computerm and then try to analyse them. -tony

Yes, of course you're replacing the laser, so you have to re-focus/colimate the beam. Fortunately when I was assembly the CX scanner, I on;y had to make sure the beak was going in the right places... 'Do not look up this laser beam with your remaining eye' :-) When I have a chance I;ll dig out what schematics I have of the CX and SX enginers and get copies to you... -tony

I am not sure how rigid polymorph is, personally I'd rather machine a metal bracket... It's a bit harder than that (at least on the CX). The laser mount and lens mount are 2 separate parts, one has a convex (spherical) face, the other concabe. There are a couple of screws to lock them toeghter, but you have enough movement to be able to direct the beam by shifting the laser mount. And of course I had to do that. But the complete assembly will come off and go back with no problems. OK, but remind me if I don;t make a comment fairly soon... -tony

But are replaceemnt CCD sensors for most video cameras any easier to find than replacement eyes? -tony

My expeirence in getting parts for camcorders suggests that CCDs and human eyes are equally difficult to obtain and replace -- that is almost impossible ;-) If you want to replace the image sensor you pretty much do need to get the exact same model (or at least a closely related one...) That is problably sensible. I've said many times that hte 3 parts of me that I depend on are my vision, my hands, and my brain. Most other things (legs, hearing, etc) I could maange without (this does not mean I am goign to deliberately harm myself), but I use the first 3 for everything I do... -tony

I did not say that I wanted to become deaf (although sometimes I wish I could turn off my audio input system when lusers insist on pestering me when I am trying to do something hackish..), only that I could manage if I was dead. Hmmm. Portable audio for me involves 1/4" magnetic tape... -tony

I susptct it's actually more like what you said later... If you have a digital camera around, you can use it for this, but it's not necessirily the best tool for the job, and it's probably not worth getting one solely to use as an IR dtector. When I was setting uphe CX scanner, I used a simple remote control tester that I'd built from a Mpalin kit. A photodiode driving a 3 transisor (I think -- it's certainly discrete transistors, no ICs) amplifier, driving an LED. The amplifier is AC coupled, so it responds well to the flickering IR output of the average TV remote control. It also responds to the IR laser beam from the CX scanner being swept across the ptoodikode by the spinning mirror. So by holding the photodiode in various positions I could see where the sweeping beam was going. And I have to say that 3 transisotrs is a lot fewer than the number you find in a digital camera :-) -tony

Actually, thinking back to when I rebuilt the CX printer (early 1990s), I don;t think digitial cameras were common then. CDD image sensor analogue camcorders existed (and were well-known to have a responsie in the near IR), but were not excatly cheap. People who had them would use them to detect IR output from remote cotnrols, but nobody would buy one for that purpose alone. I have never tried on of those IR detector cards -- can you still get them. They are a card about the size of a credit card coated with a special phosphor. You 'charge it up' by exposing it to normal visible light, and then when IR hits it it give a visible glwo. Sold for checking remote cotnrol handsets, I bit it would detect the beam in a laser printer too. Sure... I am not sure why this kit didn;'t use an op-amp. There are no bandwidth problems or anything like that. It may (amazingly) have been the physical size. The thing is entirely through-hole (transisotrs in TO92 pacakges, etc) but fits in a 'key fob' case along with a 12V battery to power it. And I[ve had the thing over 15 years and never changed the battery. Yes I do use it sitll (last time was to see if the reason my HP IR printer wasn't doing anything was because the calculator I was using it with wasn't sending anything...) The Maplin tester is entirely qualitiative. If it gets IR, the LED turns on. You can get some idea if a remote control handset is going weak by seeing how far away you can detect it, but nothing more. I think gettting any sort of meaningful scale on a meter would be very hard. The chartacterisitics of the photosensor are probably not that well known (at least not for cheap sensors). Making an IR photometer is a much harder project :-) Shunt the meter suitably (a resistor of 1/9th the resistance of the meter coil) and put it in series with the LED? -tony

No, but fast op-amps have this habit of turning into oscillators (== adio transmitters) if you look at them wrong. Layout, decoupling, ground planes, careful design of the feedback network, etc are not optional. Of course. The laser current is critical. Too low and it doesn't lase. Too high and it never lases again!. Within that range it had to be set according to the sensitivity of the drum. It was cerefully designed (I did say it was complicated). IIRC it switched the current source between the laser diode and a dummy load accordinmg to the state of the drive input. It had to work at nearly 30MHz. And BTW, overshoot on the drive currend will do nasty things to the laser diode! That's _unofficial_ of course... Includes every part of the printer. Even the PSU and EHT block. I will see what I can do. No. The motor runs a a constant speed (controlled by the PLL taking the feedback from the FG coil in the motor). The bistream runs at any speed you like (within reason), controlled by a crystal on the formatter board (or the VDO interface, or ...) The motor will ru at the right speed even if the rest of the machine is malfunctiuoing. The CX makes this a bit clearer. since the motor controller for that is a separate PCB on the bottom of the scanner module. It has (IIRC) 4 connecitons --power, ground, motor on/off and an 'up to speed' feedback signal. Sounds right. The OIO boards fit all classic PERQs (it's the only board that is totally universal like that). AFAIK the 3 OIO versions (ethernet, cannon, etherent and canon) were all built on the same PCB, with just different ICs missing. Some of the prototypes/early ones were. But AFAIK all later PERQ boards were notmal PCBs. Certainly every OIO I've seen has been a normal PCB. -tony

Pete Turnbull wrote: There would also appear to be a minutes->seconds conversion missing.