Hello,
I prototyped my project (using SPI.h with a UNO which worked fine (link here to code):
I used these pins on the UNO:
10 SS
12 MISO
13 SCK
And the same pins on the Pro Mini. However, the Mini seems to pull pin 13 down to 2V and the serial bus that I'm trying to read doesn't start.
Am I missing something code or hardware related between the two that I should be aware of? I do see that the Mini has an LED on that pin - could / should that be disabled?
Thanks all,
-C
Remove the LED on pin 13 and try again. Use the tip of a hot solder pencil to swipe it off.
You almost certainly have a cheap knockoff, perhaps with the incorrect current limiting resistor.
The LEDs on pin 13 of UNOs and Pro Minis, most always are of no impact.
If they were there would be large numbers of users having problems with SPI on UNOs and Pro Minis.
The pin 13 LED is there, and there is no magic command that would cause the LED to be ejected from the board.
There's no LED eject command?
It is a Sparkfun model. I have two that act the exact same way. I could try removing the LED on one of them.
How, exactly, are you measuring the voltage on pin 13? If you remove all the SPI connections, do you still have that problem?
If you have the genuine Sparkfun Pro Mini, then there should be no problem with the LED. More likely, you have a wiring error, a solder bridge or some other mistake.
Please post a photo of a hand drawn wiring diagram and a close up, focused photo of your board and wiring.
How is that supposed to work? Pin headers are intended to be soldered to the board.
If the header is not soldered in there will be intermittent contact and all kinds of problems. Yes, we have had posters here that had that problem
Yeah I know. The first one didn't work, so I assumed I screwed something up, desoldered it, and ordered another.
The way it's oriented I can press the arduino down on the headers and see the V drop on the affected pin. Not ideal, but ideally I don't want to solder the thing down again until I have this figured out.
Look for damaged vias and/or solder bridges on the Pro Mini board. The real problem is something like that.
You must carefully solder header pins to the Pro Mini, for this project to work.
I haven't soldered the new one down, it's pristine. I do fancy myself a good solderer, if not a bit impatient.
The problem is repeatable with both Minis. I'll dig in further if there's no inherent hardware / software configuration issues between the Uno and Mini.
Don't expect the Pro Minis to work until header pins are properly soldered onto the PCB.
Good luck with your project.
I double checked all my wiring - there's no solder bridges or anything. I'll post pics soon.
I removed the LED from one Mini, it now works, the one with the LED Pulls pin 13 down to 2.2V.
No clue why, it could just be the particulars of the hardware I'm pulling the serial data from. Or coincidence / my luck.
With the SCK pin on the Pro Mini as an input then it wont draw any current.
If SCK on the connected device is connected to 5V via a weak pullup or similar you would expect the LED on the Pro Mini to conduct, it might even glow dimmly.
So with a relativly low series LED resistor on the Pro Mini 2V on the Pro Mini pin 13 sounds feasible.
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