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I have working system with Raspberry Pi B+ and 7 relays (via ULN2003A to provide 12V to relay coil) connected to it via GPIO pins. That is all ok (working perfectly), but now I would like to read relay state via GPIO input pin. What are current specifications for Rasbperry Pi B+'s BCM2835 main processor GPIO pins, becuase I have to downgrade relay coil voltage +12V to GPIO's 3.3V?

  • There has been no change to the GPIOs. They are still 3V3 and should not be asked to source or sink more than 16 mA. Why do you think the relays may not be in the set state? – joan Sep 7 '15 at 9:18
  • @joan I do not know, I would like to setup GUI on touchscreen according to relay state itself, not it's status variable in software. So, if I connect cca 1K resistor to port, it will be ok, yeah? – KernelPanic Sep 7 '15 at 9:21
  • You may have to draw a schematic of what you want to measure. If it is the voltage over the relay coils you will probably need at least back EMF protection as well as a voltage divider. Perhaps a question on electronics stack exchange would attract the right sort of attention? – joan Sep 7 '15 at 9:26

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