On 02/10/15 18:18, Grant Likely wrote:
On Fri, Oct 2, 2015 at 5:11 PM, Daniel Thompson firstname.lastname@example.org wrote:
On 02/10/15 10:49, Grant Likely wrote:
Based on #3 I cracked open by programmer and short circuited R7 (i.e. bypassing the programmer boards current limit on SCK). With this modification I was successfully able to program the sensors board.
Any chance of a transistor switched LED circuit for SCK in v2? ;-) It would be good to be compatible with this fairly popular programmer.
Great work! Thanks for the debugging. Yes, I'll either put in a transistor, or remove the LED entirely.
Well. From my perspective having a Blink example work out of the box is a pretty good feature. It makes getting started feel pretty effortless.
Oops, I was looking at the reset LED. I just looked at the schematic for the Arduino UNO, and it has exactly the same circuit, but it uses a 1k resistor on the LED (same as your test board). It should be as simple as changing the R to 1k on the next board. I'll get some 1k resistors delivered and give it a try.
On the UNO has a yellow LED attached to GND rather than a red LED attached to Vcc. I think both these things contribute to making the circuit work!
Based on a bit of back-of-the-envelop scribbling...
I think with the UNO circuit the AVR will see logic levels of 0V and ~3.2V; not perfect but it should work.
On sensors board, even with a 1K resister we will get logic levels of ~2V and 5V and this (probably ;-) won't work.
Note that the voltage dropped by the LED contributes to circuit robustness so in addition to changing the circuit, swapping the colours of D3 and D2 (so PB5 is green and PWR is red) would definitely be worthwhile.
 Based on logic levels I found in: https://learn.sparkfun.com/tutorials/logic-levels#arduino-logic-levels