I've got the prototype all soldered up. Took about six hours, including microscope inspection, mostly for the 01005's.
The design "works". I say "works" because the oscillators oscillate (about 400Hz), the xor gates xor, the led drives work just fine, although I could have used larger resistors on the leds - the schematic says 220 ohms, but for some reason I bought 150 ohms. I think I was thinking "green led" which has a higher voltage drop. Still within spec even so. See: http://www.delorie.com/pcb/smd-challenge/smd-challenge.sch http://www.delorie.com/pcb/smd-challenge/smd-challenge.pcb http://www.delorie.com/pcb/smd-challenge/smd-challenge-sch.png http://www.delorie.com/pcb/smd-challenge/smd-challenge.png However, the two oscillators tend to self-synchronize. If I let it run, one LED is on and the other is off. If I put scope probes on the buffered outputs (pins 6 and 8), I can see that the oscillators are running, they're just in lock-step. Not even out of phase. If I put a scope probe on either feedback line (pins 1 or 13), they drop out of sync and the two LEDs pulse back and forth (about 17Hz). Also, if I put probes on both xor outputs, they drop out of sync, too. Sometimes they stay unlocked if I remove the "on led" led's probe but leave the "off led" probe there. Ideas? The only thing I can think of is inductive or capacitive coupling, but at 400 Hz? Oh, runs just fine without the XOR chip, but I tried two different xor chips, both do the same thing. DJ _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
