Timeline for Does my GPIO Expander have a floating pin? [Button and pull-up resistor]
Current License: CC BY-SA 4.0
15 events
| when toggle format | what | by | license | comment | |
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| Mar 5, 2024 at 5:07 | comment | added | Nate.Olson | @DamienD You helped me to discover my rookie mistake, it was a coding issue. The IOCON register has a bit "BANK" which moves the location of various registers, including itself. I would write IOCON, go to write/read it again, and it had moved (from 0x0A to 0x05) along with the GPIO registers, which makes it clear why those were reporting nonsense data and why certain pins were held high (I was not writing to the GPPU register but rather its previous location). Thank you so much! Sorry to take you on a wild goose chase. | |
| Mar 5, 2024 at 2:34 | comment | added | Nate.Olson | @DamienD I will draw one in a moment. | |
| Mar 4, 2024 at 9:58 | comment | added | DamienWontContributeToAITheft | @Nate.Olson can you show the circuit diagram and maybe a photo of the chip in situ? | |
| Mar 4, 2024 at 2:06 | comment | added | Nate.Olson | Even with nothing connected to the MCP23017 pins, the GPIO register holds ever-changing noise even though pull ups should keep it steady at 5V. The wiring is very clean, I'm not sure what could be causing this. | |
| Mar 4, 2024 at 1:53 | comment | added | Nate.Olson | @Attie The MCP23017 datasheet specifies that it has a 100k internal resistor, is that an issue? I understand that the pin can't simultaneously be 4.8V and .2v, but that's what my multimer is reporting pretty consistently. This is why I suspected a floating/opendrain pin? I trust my soldering, as it's visually very clean, but as I mentioned in another reply, there is a lot of random noise on the GPIO pins, so I might try reconnecting everything. My multimeter shows continuity everywhere that it's supposed to be. | |
| Mar 4, 2024 at 1:50 | comment | added | Nate.Olson | @Abel They are mechanical switches, so open line when unpressed and a resistance of 0 when pressed. I've measured this and verified. No voltage drop at all even with pull up resistors enabled on all pins of all 4 expanders. | |
| Mar 4, 2024 at 1:44 | comment | added | Nate.Olson | @DamienD AstroAI AM33D multimeter. I have connected the first 5 inputs to the first of 4 GPIO expanders, and the GPIO register returns random values with 0 and 8 being most common (I do get 5V on the voltmeter when measuring the 4th input pin which makes sense), I am worried that this is a result of damaging the buttons (cherry MX switches with the adafruit breakout board) during soldering, although the solder job is very clean and visually shows no issues. | |
| Mar 3, 2024 at 22:46 | comment | added | Attie | It's not posible for GND->Pin to measure 100-200mV, and Pin->VCC (5v) to also measure 100-200mV... do you trust your measurement equipment (cables in the correct holes, DC not AC, high-impedance, etc...) and technique (definately making good electrical contact)? | |
| Mar 3, 2024 at 22:45 | comment | added | Attie | Note, at VDD=5v, the pull-up is spec'd at 75µA typical (40-115µA), not 100kΩ. | |
| Mar 3, 2024 at 22:10 | comment | added | Abel | Check the resistance of the button in the open condition vs the internal pull. Check the voltage when the button is not present and the voltage you are giving the expander. Sometimes using too many expanders and not having enough current for all their pullups is the issue. | |
| Mar 3, 2024 at 22:04 | comment | added | DamienWontContributeToAITheft | What voltmeter are you using, and what is the logic state of the pin as reported by the GPIO expander? | |
| Mar 3, 2024 at 21:59 | history | edited | Transistor | CC BY-SA 4.0 | Please don't leave out "I am", the sentence subject and verb. The sentence isn't one without a verb and doesn't make sense without the subject. |
| Mar 3, 2024 at 21:54 | history | edited | Nate.Olson | CC BY-SA 4.0 | edited title |
| S Mar 3, 2024 at 21:53 | review | First questions | |||
| Mar 3, 2024 at 22:09 | |||||
| S Mar 3, 2024 at 21:53 | history | asked | Nate.Olson | CC BY-SA 4.0 |