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I just got my first Raspberry Pi Pico and I don't have any experience in electrical engineering.

The book I'm following indicates that I first have to solder the and the first step is to solder the header pins. I don't have any experience in electrical engineering.

Now after I finished soldering I want to test if the soldering went well. As I want to now that this step went well before moving on to actually building something.

I have a multimeter at my exposal.

I can test for short-circuits between neighbouring header pins, by doing a resistance test with the multimeter.

Now I think one can also do a continuity test, to see if the soldering connections are proper. My question: how can I perform a continuity test for all the pins? Can I just connect my multimeter with a resistance measurement to the ground pin and then one by one to the other pins? (Or is this nonsense and potentially even damaging the Raspberry Pi Pico?) (And is there a difference between General Purpose IO pins and the more exotic pins?)

The pinout can be found here: Pico-R3-A4-Pinout

I see here (https://m.youtube.com/watch?v=iIQ14vTxVK0) that a continuity test is also simply a resistance test, but in this case the resistance should be low.

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    \$\begingroup\$ If you do a continuity test from all pins to ground, you are just checking if that pin is shorted or not to ground, which is not very useful, as all pins that are ground are supposed to be connected to ground and all other pins are not supposed to be connected to ground. \$\endgroup\$
    – Justme
    Commented Jun 1, 2023 at 9:07
  • \$\begingroup\$ @Justme makes sense, how then can I test if the soldering connections are done well? \$\endgroup\$
    – Jens Wagemaker
    Commented Jun 1, 2023 at 9:09
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    \$\begingroup\$ Visual inspection is normally fine if you know what to look for, have a search for some basic guides. I suggest you practice on something less expensive to get the hang of it! \$\endgroup\$
    – Finbarr
    Commented Jun 1, 2023 at 9:47
  • \$\begingroup\$ Proper soldering isn't (solely) tested by checking if everything conducts as expected, but also by looking at the quality of the joints themselves. Professionals inspect solder joints using microscopes and automated optical inspection (essentially cameras). Now as a hobbyist you won't have access to that, so a magnifying glass might be a decent compromise. All of this assuming that you know what a good solder joint should look like. \$\endgroup\$
    – Lundin
    Commented Jun 2, 2023 at 6:59

2 Answers 2

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The book I'm following indicates that I first have to solder the and the first step is to solder the header pins. I don't have any experience in electrical enginering.

The first thing you do to test that board is to just connect it to a PC via a USB cable, without soldering anything, and ensure you can connect to it and upload firmware.

Now after I finished soldering I want to test if the soldering went well. As I want to now that this step went well before moving on to actually building something.

There are two types of faults you want to check against:

  • shorts between adjacent pins, and
  • opens.

Shorts have to be tested for first. To do that, set all configurable pins as outputs, then run all possible bit patterns on them. Read those bit patterns to compare. What you read back from the pin must be the same as what you wrote. It's easiest to access all those pins as the a 32-bit register, and run a loop from 0 to 0xFFFFFFFFu.

To test for opens, you'll want to keep all pins toggling between 0 and 1 at a slow pace (a couple Hz), and use an LED to connect to each pin and see if it toggles.

That should verify that everything is OK with the soldering of the GPIO pins.

Shorts of VCC and GND pins will be self-evident since they'll either prevent the device from working at all, or will affect the adjacent GPIO pin.

Opens of non-GPIO pins can be found using the LED as well: VCCs should light a led going to GND, GNDs should light a LED going to VCC.

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    \$\begingroup\$ "There are two types of faults" There is actually the third kind which is a poorly made solder joint which will conduct as expected today but maybe not tomorrow. These include poor wetting, cold joints, wrong amount of solder etc etc. \$\endgroup\$
    – Lundin
    Commented Jun 2, 2023 at 6:55
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To be honest, the best test you can do is a visual inspection of the soldering under a magnifying glass.

After that, I'd write a program to briefly set each pin on in turn, with all the others off, and use the DMM to check the voltage on that pin. The voltage should be close to 3.3V when on, and 0V when off; anything outside those suggests there is a short-circuit to another pin, or an open circuit.

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