On 11/1/06, DJ Delorie <[EMAIL PROTECTED]> wrote:
I played with the op-amp idea, and actually got a working prototype on proto-board. http://www.delorie.com/pcb/io_port4.sch The "out" (line-driving) op amps come in a tiny dual-amp package, and the use of resistor dividers and ability to swap +/- inputs lets it drive the two MOSFETs directly. The "in" (sensing) op amp uses a divider to bring 0-5v down to 0-3.3v, with the reference suitable for both 3.3v CMOS and 5v TTL levels (effectively 1.65v). That op amp is available in a SOT-325 package, making it about as big as a transistor. The use of op-amps also nicely solves the voltage conversion issue, letting me run the R8Cs at 3.3v while still driving the thermostat lines at 5v.
Be sure to check how long it takes the op-amps to come out of saturation if you intend to use this for high-speed signals. Comparators (ones with totem-pole outputs) are usually better suited to this application. Regards, Mark [EMAIL PROTECTED] -- You think that it is a secret, but it never has been one. - fortune cookie _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
