DiscFerret: Update 2010-11-03

I've made a bit more progress with the DiscFerret: * Cost reduction I found another PCB supplier who can supply PCBs of a similar quality to the Eurocircuits boards, but at HALF the original price, with full electrical testing and RoHS compliance thrown in. There is a catch, though: I have to order a panel of six boards at a time. Assuming the quality is at least as good as the Eurocircuits boards, this is what I'll be using for production DiscFerrets. Bare board cost is now down to ?25 including UK post, down from ?52. The price for a board with the TPS75003 pre-soldered is set at ?29, or ?4 more than a bare board. This includes me doing a full continuity check on the TPS75003 and surrounding tracks. I've ordered half a dozen boards, which gives me ten saleable units. Depending on how many orders I get, these will probably be a mix of bare boards and fully assembled and tested boards. I intend to keep a few boards in stock (the P&P is included in the board price, so "just in time" ordering is a real possibility). * Board changes I've made the pads larger on the Schottky diodes and inductors. It should now be possible to solder these with a soldering iron! For obvious reasons I'd suggest a temperature controlled iron (Antex 660TC with TC50 iron, Weller TCP, Xytronic or similar), but you should be able to get away with using a 25W iron (Antex XS or similar) and a 2.5mm bit. There are a few 0805 parts nestled amongst the 0603s. I've tweaked the pads on these so that 0603-sized parts can be fitted in place of the 0805s. * Reflow profiling I think I've mentioned that the power controller chip can't be soldered with a soldering iron. I spent a few hours yesterday ruining parts^W^W figuring out a usable reflow profile for Multicore RA15 SnAgCu solder paste... Turns out the process parameters for hot-air are "slightly" (read: completely) different to the parameters given in the datasheet. Anyway, it works now, with a small amount of rework needed afterwards (wicking away a bit of excess solder on the pads). * Write support You heard it here first, folks: disc write support has been added to the DiscFerret microcode! This puts the DiscFerret well in front of the SPS Kryoflux analyser (which, at the moment, is read-only). I'm working on a proper test suite for this, but initial results look promising. There are a few other things I'd like to add before release: * Head settling time enforcement. The seek logic currently ignores settling time. This is going to be added before the final spin, come hell or high water! * Index frequency measurement. This would be handy for setting up speed-adjustable drives like the Amstrad/Panasonic EME series 3-inch units (used in the CPC and PCW series and the Spectrum +3). It should be possible to get at least one reading per second with a decent amount of resolution. The plan is to get some early-production units made up and on sale by the end of the month, and do another production run early next year if there's sufficient demand. Cheers, -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/