¢HARDWARE WAREHOUSE - FUTURA ISSUE 12¢¢¢BUILDING A 1050 WRITE PROTECT SWITCH¢by Alan Hitchen¢¢ The most annoying aspect of owning a disk drive is the write protect notch. The tricky business of cutting out a notch to use the flipside of a disk and then sticking and unsticking labels to protect and unprotect the disk is something we could do without.¢¢ The answer of course is to install a write protect switch. A ready made kit is available from Micro Discount for 7.95 (reviewed in New Atari User 58), but as I have some experience of DIY electronics I decided to make one of my own. ¢¢ In New Atari User 43 there is an article on how to build your own switch, written by Derek Fern, Mr Micro Discount himself. All the components may be bought from Maplins as detailed in the article. But I began by unearthing the items required from my own collection of parts. I found I had plenty of wire, but no four way minicon socket. I considered making individual terminals before finding a broken IC socket from which I cut a section to suit. The switch specified was a DPDT toggle but I used a slide switch to fit the case I had selected, as to avoid damage to the disk drive I decided on a separate box to hold the unit. I found that the 60x60x20mm plastic case from a 1289 torch battery would do just fine. The plans showed a two in one LED and the latest kit version uses a flashing two in one. As I had neither I used two standard green and red 5mm LEDs. ¢¢ Starting with the battery case, after discarding the contents I drilled the base for the cable entry hole. Next the lid was drilled for the two LEDs and the switch. The switch needed a rectangular hole so pilot holes were carved square with a Stanley knife. I had intended to fit the switch internally using bolts or glue. However as I had damaged the lid while carving the hole I decided to fit the switch externally as an interference fit to cover this up.¢¢ Having installed the switch and LEDs in the lid I then wired them up, with sleeving as required to prevent short circuits. The wires to the socket was then fed through the hole in the case and the lid glued on.¢¢ Unscrewing the disk drive I removed the top of the case. I decided to position the switch box at top left front and stuck it down with Blu Tak. I then fed the wire through one of the ventilation slots and soldered the socket on the end to complete the construction.¢¢ I located socket J11 at the left side, first in a line of sockets when looking from the front. It was tight, so I used needle nose pliers and gently unplugged it, and then tucked it out of the way. Using the pliers again I inserted the new socket onto the top three pins (the first pin is unused), making sure it was the correct way round. I then reassembled the drive casing and the job was complete!¢¢ Testing proved it was working correctly. However I noticed that the red LED was very bright. Checking this with my multimeter I found that the current was too high at 26mA. A series resistor was needed to limit the current to around 10mA. Adding a 240 Ohm resistor solved the problem nicely. The green LED was within its limit at 24mA. Adding a 100 Ohm resistor would bring it down to the ideal 20mA but I didn't bother.¢¢ For those who want to have a go I have drawn up a circuit diagram in a Koala format picture. Run SWITCH.BAS to see this, press any key to exit. Unlike the original plans I wired the switch to show red for write and green for protected. The components I used were supplied by The C.R. Supply Co., 127 Chesterfield Road, Sheffield, S8 0RN. Send a stamp for their latest lists. They are cheap but only stock a limited range of items. Please remember to check the polarity of whatever type of LED you use. The standard 5mm type I used mark the cathode (-ve) with a flat on the case and a short lead. ¢¢ Needless to say only attempt this if you know what you are doing, don't blame me or Stuart if things go wrong. If in doubt don't do it yourself - try the Micro Discount kit instead. And please remember that protective labels are defeated by the switch so be careful when writing to precious disks. Finally I must say after using a write protect switch I wouldn't want to be without one again.¢¢¢-----¢¢¢ED- If you have an Atari 8-bit hardware project, review, tip, etc. please send it to me at the usual address. Free NOSAUG PD disks are given for any article used!¢
