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61361Maggie (was: Magnetic Tracking Herbie circuit)

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  • country_robot
    Jun 11, 2014

      I'm calling robots that follow and record magnetic trails "Maggies" to save typing.

      I've also uploaded another, much more complicated circuit schematic (a magnetic tape read circuit from the February 1977 Byte Magazine article "Digital Cassette Subsystem, Part 1"). I've cleaned the scan up a bit and made it slightly more compact, but I haven't introduced any changes to the circuit (at least not on purpose). In particular, I've kept the original component values and callouts to keep from introducing any confusion for folks who want to look at the original scan.

      It calls for four op-amps, two low-noise audio preamps, some logic gates, heaps of resistors, capacitors, several trimpots, and ±15V and 5V power supplies—and that's just for one read channel! Obviously we can do better with today's parts. Heck, there are probably single-chip solutions used for floppies or old QIC tape backup systems that might be coerced into doing the job. These chips, though, won't be as easy to apply since they assume a much faster magnetic surface speed than the 2 to 4cm/s Maggies might provide.

      The bone-headed approach is just to replace the preamp chips with one dual preamp of similar or better specs and likewise replace the single op-amps with a quad. But is there a better way? What functions of the circuit are essential and what can be dispensed with?