Tx and Rx LED headers, just to be sure of specs and wiring-

Dgephri · Post by **Dgephri** » Mon Nov 22, 2004 11:56 am

Tom has assisted me on other issues for the GPOs and Fan headers, but now I am down to designing some LEDs for the Tx and Rx headers on the 520 model:

Page 13, figure 8 depicts the LED Tx/Rx header, and as labeled, it shows the LED pin heads on the right side, but the only Gnd is on the Left. Do they both need to Gnd at the lower left pin? Or is it +5V then over the LED header both on the right side?

Oh, and the PDF says they are current limited to 20mA, so if I run a 3V LED at 20mA I don't need an inline resistor added?

Tom · Post by **Tom** » Mon Nov 22, 2004 12:49 pm

The anode of your LED will be connected to +5V and the cathode will be connected to the RX/TX header. Only the pins on the right side is for the LEDs. The pins on the left side is for TTL communications. You won't need a current limitting resistor because it is already current limited to 20mA as shown in the PDF.

Best Regards,

Dgephri · Post by **Dgephri** » Mon Nov 22, 2004 1:37 pm

thx again tom, I just didn't want to be hooking up two positive leads, and crisp either the unit or the LED.

So, +5V on the right side, then to the Rx or Tx pin for ground eh? Nice, which is kind of what I expected, you guys generally think ahead on the board layout that we can use plugs instead of needing to reach individual pins.

Again, thanks for the confirmation.

Dgephri · Post by **Dgephri** » Thu Dec 30, 2004 10:10 am

BTW, was just thinking about a couple things using the Tx/Rx LED headers:
1.) They flash with USB comms too right? Not just Serial comm....
2.) is there a way to control if they are on/off without unplugging them? ie-I want the whole unit dark, and all lights off? Or should I just send LCDC a sshutdown signal?

Tom · Post by **Tom** » Thu Dec 30, 2004 12:14 pm

1) The TX/RX LEDs will only work on USB communications.

2) The LEDs are not for controlling. They only indicate whether data is being transmitted or received. If you shut LCDC down or get the LCDC to stop sending or receiving data the LEDs will stop blinking.

Best Regards,

Dgephri · Post by **Dgephri** » Thu Dec 30, 2004 12:35 pm

(quietly rubs hands together)....excellent.

As always, great help Tom!

This one will definitely get put up in your gallery: 5 LEDs running a Fiber Optic starfield with a mirror-box light pump housing the LEDs.

so, the arrangement is that 3 LEDs (2 white, one blue) are running off the low power GPOs, and the other 2 (one white, one blue) will flash with the Tx/Rx activity. This should work out to give a nice, randomizing twinkle effect.