Built a perfboard arduino with the standard 6 pin connector (pin 1 grnd, pin 2 cts, pin 3 5v, pin 4 tx0, pin 5 rx1, pin 6 dtr) for programming (using a sparkfun bob)
Is there a led circuit I can put on or in between the atmega328 pin 2 ( pin 0 RX ) to interface pin 4 tx0 and atmega328 pin 3 (pin 1 TX) to interface pin 5 rx1 that can show serial activity without the chance of corrupting the data stream.
I know its simple but I want to make sure Im not missing any hidden downfalls, the sparkfun BoB has leds for activity but I want a second dedicated set on the standalone.
Thanks I thought so, but was concerned there was some "hidden" noise garf I was missing or something, that someone might have had previous experience with.
The serial will still get through even with ground involved?
As long as the signals are standard logic then they will drive a led as well as the AVR inputs. Even if you wind up putting your leds in parallel with those already on the BoB the logic should drive them both.
I'm not entirely familiar with the hardware you're using but the above should hold true unless something weird has been done.
The bob leds are driven by the FT232RL chip as a side function to the rx tx serial transfer.
Here is a pic of the BoB as it hooks up to the standalone.
My concern was that a led circuit to ground would sidetrack the data flowing through serial rx tx, I need to send and receive data, on some projects, while still connected to the computer, not just for sketch uploading. I was just concerned about data corruption and wanted to make sure there was any hidden traps.
OK I've just had a look at a SFE BoB schematic (don't know it it's the same as yours but they are probably all the same in this regard) and they have the LEDS connected to VCC, presumably because the line idles high and that way they will off mostly and light when data is flowing (makes sense).
So having your LEDs to ground as I first suggested will look like this.
This will work but your LEDs will be inverted, ie. light when there is no data and blink off when there is. Probably not what you want. So by connecting yours to VCC as well they will work the same as the existing BoB LEDS.
I have a FT232RL data sheet, I can see no mention of the drive capability of the Tx line but would assume it's Ok with driving the two LEDs in parallel. If it can't then an advantage to schem 1 is that it only ever drives one LED at a time.
So, I'd connect your LEDs to VCC as per schem 2 and see how it works, I can't see any way you'll kill either device.
If you're application has something else connected to these lines as well that's another issue.
