As far as I know you should be able to use a Gertboard with a RPi 4 using a 26 pin ribbon cable connected to the first 26 pins of the GPIO connector like it was
done when they originally changed over to the 40 pin connector. There are differences in GPIO register addresses between 256 MB, 512 MB, and 1 GB (?) RAM
versions of the earlier RPis, and I believe the RPi 4 has different register addresses than all of the previous versions, that will prevent older software from working
without changing the addresses in the software first. The register addresses should be the same for the RPi 4 regardless of how much RAM it has. There are also
a few changes on which physical port pins on the different Broadcom SoCs are connected to the GPIO connector so software written for the earlier RPis will need
to be adjusted to fix that. There are no differences in the physical interface between the two versions of the Gertboard that I am aware of.
I have one each of both versions of the Gertboard and would be interested in finding out if anyone has modified software or a Gertboard library that has kept up
As far as I know you should be able to use a Gertboard with a RPi 4 using a 26 pin ribbon cable connected to the first 26 pins of the GPIO connector like it was
done when they originally changed over to the 40 pin connector. There are differences in GPIO register addresses between 256 MB, 512 MB, and 1 GB (?) RAM
versions of the earlier RPis, and I believe the RPi 4 has different register addresses than all of the previous versions, that will prevent older software from working
without changing the addresses in the software first. The register addresses should be the same for the RPi 4 regardless of how much RAM it has. There are also
a few changes on which physical port pins on the different Broadcom SoCs are connected to the GPIO connector so software written for the earlier RPis will need
to be adjusted to fix that. There are no differences in the physical interface between the two versions of the Gertboard that I am aware of.
I have one each of both versions of the Gertboard and would be interested in finding out if anyone has modified software or a Gertboard library that has kept up
