Insights into IDE and LED

Loihi in the box Did some research today.

Can a 80 wire IDE cable be shortened (as in: can I cut off the second device connector)? According to the ATA spec, a cable has two device connectors (but cables with only one are sold). The minimum length for one segment is 127mm, and the first segment must be equal or longer than the second. So: I'll backup the data, cut off the second segment (the first is than longer for sure), and see what happens (it works).

Do I need to limit the current for white LEDs? Merten told me that up to 4.5V I won't need a resistor. Bzzzt - wrong! There is no such thing as "internal resistance" since a LED is a semiconductor, and once the "forward drop voltage" (the voltage the LED needs - and eats! - at mininum) is exceeded the current might rise exponentionally with voltage. White LEDs have a 3.4V dropoff voltage. With 6V and a rating of 20mA, the following resistor is needed: (6V - 3.4V) / 0.020A = 130 -> 150Ohm. For 12V that would be 430 -> 470Ohms, or 260 -> 270Ohms with 2 LEDs in series, or 90 -> 100Ohms with 3 LEDs.

How can I drive LEDs with the Basic Stamp? Parallax offers a Darlington Array at $1.50 which directly connects to the Basic Stamp and is able to drive up to 500mA on each of its 7 outputs. Neat! Maybe Merten has it. Phoned. He has! EUR0.95... So, now I can switch my LED lights on and off computer-controlled.

Cut off IDE cable after 2nd connector and folded it as neatly as possible. System still boots, have to check if BIOS still believes it is an 80 wire cable. Tried out the computer box closed. The fan is pretty noisy, even more so with the lid on. I need to verify this with a thermometer, but I get the impression cooling might be quite good because passages between heat sinks and box are pretty narrow (funnel effect).

Connected the (screaming bright red) sleep LED. Was not really needed; I saw the power LED flashes when the board goes into suspend mode. Finished one more flat serial cable for connection with the on board headers. Read up on header pin out, and soldered a flat serial cable to the Basic Stamp board. Will need two capacitors for finishing that part, though.