Here's a quick one.
Into every EE life, a little RS232 must fall. They tell me that most serial ports can deal with TTL-level signals, now, for their inputs. I'd suspect, though, that they have not yet completely moved over to that sort of compatibility with their outputs, and, sure enough, my computer is still spitting out something like +/- 10V. So I hereby present Yet Another Serial Level Translation Board. This one is nanoSTACK-shaped, though.
It also has the possibly neat bonus of posessing little blinky lights. These are important. They are also reasonably clever, in that they light up for both levels of signal (they are bicolor; it would be less interesting if they weren't). I obtained some of the less-common bicolor LEDs, the ones with only two leads. As seen of the schematic below, they are driven with a high-power inverter in "push-pull" mode. Now, there is some unbalanced latency in the system; I spent some time wondering if the few more nanoseconds (2-5, or so) it takes a signal change to propagate through the two inverters on the one side, than the single one on the other, would make Some Kind Of Difference. I have concluded that it does not.
Note also the 'AC series logic. You've got 24mA of LED driving power there (sink and source, whoo!); trying this with 'LS logic, or 'HC (shudder) Wouldn't Work.
No one else seems to do status indicators like this. I'd appreciate any examples, or feedback on Why Not.
I gotta get a better schematic package:
Headers A & B are the standard nanoSTACK alpha & beta headers.
You know, there's like three different errors on here? HS1-1 should be connected to HA-1, and the signals on HA-4 and -5 should be moved to HA-7 and -8 (respectively). You'd think I'd get the schematic right; I drew it from the board I built...! I'll wait until I redraw everything in Eagle to fix them, though.
<actual picture soon to come>
|Last updated September 3, 2004||
Original content copyright © Christian Weagle unless otherwise indicated.