Raspberry Pi 4 Model B GPIO pins for Langstone (Pluto)

[n5bravofoxtrot]

I have a Raspberry Pi 4 Model B which has a 40 pin GPIO connector. The physical pin numbers and GPIO numbers do not correspond to the information at https://wiki.microwavers.org.uk/Langstone_V2#GPIO_Pins . Researching online, I find that there were some RPs in the past (or perhaps smaller model numbers) that had 28 pin GPIO headers and on these, physical pins 11 and 12 do correspond with GPIO 0 and 1 respectively which do agree with what I see in the source code, Langstone-V2/LangstoneGUI_Pluto.c lines 291 and 292. On line 293, txPin is defined as 29 corresponding to physical pin 40. This is confusing. There is no physical pin 40 on a 28 pin header and there is no GPIO29 that I have found on any diagram for 28 or 40 pin headers. My documentation says that pin 40 is GPIO21.

I was about to start testing with a voltmeter and would be happy to change the code as needed to get this working, but then the microUSB connector on the Pluto got damaged and I haven't been able to boot the system to the point of being able to do tests since then (PTT, Key, etc.)

When I get my hardware issues straightened out and get back to trying to hook up the GPIOs to external circuitry I would like to understand what is going on with the numbering and assignments. What is the latest on this?

Thanks and 73, Courtney N5BF (DM04vf)

[G8GKQ]

Hi Courtney

You are getting confused between Physical Pin Numbers, Broadcom GPIO numbers and WiringPi numbers. WiringPi is a library for driving GPIO pins which for historical reasons uses a different numbering scheme from physical or Broadcom.

Physical pin 40 is the transmit indication, it is activated using the WiringPi command for 29, but uses Broadcom GPIO 21.

Don't even think about the old 28 pin GPIO headers otherwise you will get even more confused.

This Wiki page shows (all 3) numberings for a Portsdown 4 and Langstone. https://wiki.batc.org.uk/Portsdown_4_GPIO_Connections

Dave, G8GKQ