MIDster Punch Electronics and Mk2 Machine Progress

MIDster Punch Electronics and Mk2 Machine Progress
Hi there! Can anyone advice a suitable replacement for the CNY74-4 quad opto couplers, as used in Bob Essex’s CNC punch plans? This specific part now seems to be obsolete, but these being quite rugged electronics there must be something that can be used as a direct replacement (if anyone has a couple lying around spare, please come and fine me at Twinwoods this weekend!). Also, anyone who knows of a useable pair of 500mm wide rubber-coated drive rollers please contact me! I built the control board for my machine some years ago from Bob’s plans, and having unpacked it after years of gathering dust have found it not to be working. Tests show these opto couplers to be the most likely culprits. I can manually step the motors with these couplers removed using the transistor circuit, and the PC / TTL inverter end looks fine, so I’m sure the problem is where the two circuits meet! The mk2 machine is now starting to take shape (pics coming soon!); this uses a motor and cam permanently mounted at the side of the unit, rather than solenoids as with the mk1 (which would punch fine with thin card, but not reliably enough for thick stuff, hence I abandoned this and moved to the next idea!). Consequently the head is very light so it can traverse quickly. I’ve presently got a direct-drive traversing stepper motor linked to the head by 6mm pitch timing chain and sprokets, though until I’ve got a stepper motor drive circuit working I haven’t been able to -*test*-('") this to know if the gear ration and motor torque are suitable. I am going to be expanding upon the amount of control quite extensively for my machine, including more feedback position sensors as the mk2 is capable of perforating music up to 0.5 metres wide. I might also look at careful acceleration and deceleration curves for the steppers, along with possible ¼ and 1/8th stepping if I find this is worthwhile. I also hope to write my own software which latches on to the co-ordinate file produced by midiboek in order to give me a greater amount of control and accuracy of punching, avoiding substantial quantisation errors yet maximising speed. To achieve the latter I’m presently working on a card increment of 1mm, such that any note can be a multiple of this length and at any position to the nearest mm. This is much less than the size of the punch, and seems a sensible unit to use, though the machine won’t go back and punch 1mm out of each hole on each pass of the head, it will skip notes in order to maximise the length of the punch and save time. Kindest regards, Nick

Also, anyone who knows of a useable pair of 500mm wide rubber-coated drive rollers please contact me! What you need Nick are some rollers from 132-column dot-matrix printers or from old electric typewriters. My local surplus store in California has IBM Selectric Electric Typewriters for $20 each which have the perfect roller in them. If you are interested I could pick up a couple of typewriters, send you the rollers and ditch the mechanisms. (Trust me there is nothing really useful in the rest of the typewriter. I tried taking one apart for the fun of it... Took me 4 hours and all I had to show for it was a bunch of metal rods and some cir-clips :-) although the golf-ball print head is pretty clever !!) Anyway I doubt the postage for 2 rollers would be very much. If you are interested let me know and I'll see what I can do. FYI $20 = approx 12 GBP at the moment. Stephen

Hi Nick The CNY74-4 opto couplers: These seem to have become obsolete. You can substitute any type of 4-way optocoupler package, they are all more or less the same except that some have the pin numbers different but if you follow the diagram you can work it out. The ISQ74 package is made by Toshiba, Siemens and Isocom and has the same pin outputs. The TPL621-4 has the same parentage but the pin arrangements are slightly different. It is possible to buy these from Rapid Electronics. See their website http://www.rapidelectronics.co.uk Hope this helps Bob

Thanks for the information Bob; most helpful. Thanks also for your kind offer of help with the drive rollers Stephen. I think have however now solved this problem through use of some solid bar turned down to 1 ¼ inches and some thick smooth-bore rubber hosing/tubing. By making the rollers up myself I’ll know that they’re a perfect match and just the right size for the job, as well as having the advantage of being able to replace the rubber latter on in the machine’s life if needed. If it doesn’t work however I’ll be emailing you! Thanks again, Nick

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