- Link Activity LEDs for CALCnet 2.2
- 17 Sep 2010 11:56:31 am Permalink
As per the incessant nagging of one Alberthrocks, I have added a little link activity module to my six-calculator CALCnet2.2 hub, as well as drawn up a schematic and taken a picture of the unit in action. You'll notice that the schematic below has two identical two-transistor halves, one for the clock line, one for the data line. The first transistor in each pair functions as a logical NOT gate, because the calculator hardware specifies logical high on 0V (electrical ground). The first transistor therefore inverts this logic so that a logical low means no current through the resistor connecting the two transistors in each pair. The second transistor in each pair switches the associated LED on or off; just about the simplest transistor circuit you can make.