Raspberry pi gpio pins 27 and 28

General
1

Hi. I am writing flows for an already established hardware setup. The installation uses pin 28 (gpio 1). However, the gpio node doesn’t seem to allow me to select that pin. Any way around this? Thanks.

2

Well, if you are using any I2C devices that may be a problem.

27 and 28 are used for an I2C bus.
See this link:
https://www.jameco.com/Jameco/workshop/CircuitNotes/raspberry-pi-circuit-note.html

Now, you say The installation uses pin 28.
Which installation? I am not understanding what you are installing.

3

Thanks for the reply. I am not using i2c in these flows. The existing hardware circuit depends on using pin 28 as a digital io pin. This is based on an existing printed circuit board. I don’t know why the gpio node doesn’t allow use of pins 27 and 28 as they are usable as gpio 0 and 1 respectively in Python and other languages.

4

I'm confused.

ALREADY EXISTING HARDWARE SETUP.
To me means it is working.

And you are now adding something else and it has stopped working.

The link I posted shows you what those pins are used for.
Alas they don't say/call either of those pins GPIO 1

There seems to be more to this than you are sharing.

5

Andrew, @kxkayser has a system already built that has that pin wired up and is trying to use node-red to drive it.

@kxkayser, google seems to suggest that the pin is not normally available as GPIO in python either, but I do see that there are workarounds. I don't know whether it is possible in node-red.

Is it not possible for you to use one of the normal GPIO pins?

1 Like
6

They are not usable because they are reserved on the Pi and the node reflects that by not allowing them to be used. If you do a google search using rpi python using pin 27 you will find article after article about this for example:

I2C EEPROM

Pins 27 and 28 (GPIO 0 and GPIO 1) are reserved for connecting a HAT ID EEPROM. Do not use these pins unless you’re using an I2C ID EEPROM. Leave unconnected if you’re not using an I2C EEPROM.]

From: Raspberry Pi Pinout Guide: How to use the Raspberry Pi GPIOs? | Random Nerd Tutorials

1 Like
7

Hi Colin,

Thanks for the reply. To use another pin I will have to cut a trace on the board and rewire. Doable but not ideal. That’s why I was looking for a way to use the pin in NR.

Regards,

Ken Kayser

Tobaccoville, NC

kxkayser@gmail.com

8

Thanks zenofmud. Guess I’ll have to modify the circuit board. Not ideal but doable.

Ken Kayser

Tobaccoville, NC

kxkayser@gmail.com

1 Like
9

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