I am trying to use a NEO-M8N GPS module with the Jumperless breadboard. I chose two rows for power and ground and verified that there is 5v present using an oscilloscope. But when the GPS module is added, the 5v drops to 2.5v and the GPS module does not light. So then I wondered if this module draws too much current. Measured current and the GPS module only draws 20ma. Im curious as to what would be causing a voltage drop by half of the supplied voltage when the GPS module is added.
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Hey Crash, welcome! Super sorry I missed the notification on this.
That is a thing I’ve seen happen before (it seems to happen a lot with ESP32s), and while we’ve never definitively nailed down the cause, here’s my best guess:
I think the ~80 ohms of switch resistance gets in the way of startup on those things (ESP32s at least), putting them in a weird “half-on” state where they draw more than the current you measured when it’s running properly.
Even if it didn’t get into that state, there would still be some voltage drop at 20mA, but not 2.5V worth.
Also in general, the 4 corners of the breadboard (1, 30, 31, 60) are handled slightly differently from the rest, and can sometimes take 2 hops to get a connection 3.3V, 5V, or ground, doubling the switch resistance. So if you’re module is connected starting at row 1, try scooting it over a row and see if that helps. This was a dumb decision on my part because everyone starts at row 1, on V5 I’ve moved those “redheaded stepchildren” rows to the far right side.
My lame recommendation for now is to just put jumpers (gasp) to the rails (make sure your rail selection switch is set to 5V, the middle position) for power and ground. The rails don’t go through any CMOS analog switches and will provide as much current as your USB port can handle, so like 500-1000mA.
There is a firmware update coming eventually that should fix this by filling up all the unused possible paths with redundant connections to get the switch resistance way down. But that might take a little while.
Luckily, I happen to have one of those same GPS modules so I can test it here. Would you mind sharing your Wokwi link or a screenshot of the netlist (type n in the app) so I can reproduce the issue? Maybe it’s something else causing this so it’s worth checking.
Thank you very much for your reply. I will share the wokwi wiring link after I’m done with work.
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This is the Wokwi link that I was using. Very basic circuit.
Huh, I just ran it and yeah, drawing 20mA does seem to cause that huge drop. And it doesn’t seem to be any particular bug or anything, just a consequence of the two switch resistances (one to 5V and one to gnd) in series with the supplies.
That just moved the firmware update to make that less of an issue to the top of the list of things to work on ASAP (I guess it was #2 already but now I need to get in firmware mode again sooner.) For now, physical jumpers for power and gnd will fix it, which is friggin’ lame because it’s called Jumperless not Jumperfewer.
Also you don’t need to connect the 5V and gnd on the arduino to the breadboard, I should make it explicitly ignore those because that’s the correct way to do that on a real board.
I had already tried using physical jumpers with the 5v and Ground, and with that, the module works like it should. I really appreciate your quick responses and information provided! With this explanation, I understand why I have had trouble starting with row 1 at times, and having also noticed that wiring power and ground to breadboard from the Arduino, doesn’t seem to matter.
I have to say that I have really been enjoying the Jumperless board and being able to prototype in a whole new way. I want to thank you for all of the work that you have done to make these possible, and I will be buying the Jumperless V5!
Thank You ArchiteuthisFlux
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