Propeller Pins and com status LEDs Questions

dbritta1

I have a master Prop Proto board with FullDuplexSerial links to two slave Prop Proto boards and a RN-42 Bluetooth module.
I am planning to use 100ohm resistors in series with all TX and RX pins to detect and protect against code and cable faults.
I am planning to use 1K pull-down resistors on the RX pins to detect cable faults.

I would like to add small green LEDs to indicate proper communication status.
I have some unused Prop pins that could be used in code to drive status LEDs.

In this case, I presume a series resistor on the Prop pin and the LED to ground would be appropriate.
QUESTION 1) What would be a good value for the resistor to compromise between visibility and current draw?

QUESTION 2) Is it possible to add the status LEDs directly to the RX and TX circuitry without degrading the com performance?

kwinn

With high efficiency red leds you could use a resistor in the 680 to 1.2K range and have good visibility.

Peter Jakacki

dbritta1 wrote: »

I have a master Prop Proto board with FullDuplexSerial links to two slave Prop Proto boards and a RN-42 Bluetooth module.
I am planning to use 100ohm resistors in series with all TX and RX pins to detect and protect against code and cable faults.
I am planning to use 1K pull-down resistors on the RX pins to detect cable faults.

I would like to add small green LEDs to indicate proper communication status.
I have some unused Prop pins that could be used in code to drive status LEDs.

In this case, I presume a series resistor on the Prop pin and the LED to ground would be appropriate.
QUESTION 1) What would be a good value for the resistor to compromise between visibility and current draw?

QUESTION 2) Is it possible to add the status LEDs directly to the RX and TX circuitry without degrading the com performance?

Unless you are using cheap bargin bin LEDs (don't) then just use good quality high brightness LEDs but still cheap and you will find 1K will be very bright. This also gives you the option of using a larger value resistor if you need to.

Suggestion: skip the pulldown resistor as it is incompatible with directly driven LEDs or else use a cheap gate or I/O to drive the LEDs if you still want the pulldowns. Without pulldowns but still having a series resistor you can test your receive lines by pulsing them low briefly then allowing them to float again as inputs then reading the state of them several microseconds later. If they are still low then there is nothing pulling them up which indicates a fault.

dbritta1

Gentlemen,
Thank you for comments.
Will likely use seperate IO pins for status LEDs, this way, they can also indicate packet checksum and other types of com errors.