extend I2C

[paulwratt]

32 RPi is kind nice, but still small for a build farm.

You could add the following option (or something similar) to extend it to 128: https://github.com/fenlogic/multio

[Terminus-IMRC]

Thank you for the information! However, because most of the pins between clusters are dedicated to power (1 * 32 = 32amps!!), extending GPIO of Raspberry Pi itself is not preferred.

The 32 limitation is because MCP23008 (I/O expander) can only change least significant 3 bits (2**3 * 4 = 32). So I'm thinking of having I2C address exchanger, and using both I2C0 and I2C1 of Raspberry Pi.

[Terminus-IMRC]

Oh, the board you linked uses MCP23017, which is 16-bit version instead of 8-bit, so 2**4 * 8 * 2 = 128!

[paulwratt]

I just picked up 2x of these: https://bmdesigns.com.au/shop/relay128-128-channel-relay-driver/

This board uses the I2C Based MCP23017, Featuring 8 on board for a total of 128Channels!

one for my camper (local use), one for my mothers place (remote use).

I also have a tiny 250 watt buck-boost convertor, so at 12v0 in, and 5v1 out, I can supply 20-50A worth to combinations of RPi, USB-HD, USB-HUB+SSD, 10/100 HUB. I dont think my "house" battery in the camper supply take 50A for very long though ;) Still, at most its 15 RPi4 (safety calculations) and I have a 60A charge controller comming too.

I can use a mains 12v0 or 5v1 DC supply at the remote site, to run more RPi4, however 3A per unit is expensive on a solar battery setup, but on mains its practical.

Anyway, I am glad someone else tried a 128 channel I2C board, and I was around with the funds to get 2x of the last 5.

[Terminus-IMRC]

Nice product! How are you going to supply 5V and 128 Amps, and how do you install the Pi's (GPIO, serial, and wired LAN cables)? We are suffering from spaghetti cables that prevent us to move them along in our office... 🪢

[Terminus-IMRC]

Thank you for editing the post, I'd like to have some pictures of your 128 pis running at the same time if you succeed to manage to supply the hugeous power😎

[paulwratt]

I wasn't expecting you to reply so soon, I forgot its 4:00AM here :)

I found a nice (reasonable priced) 850 watt 5v2 power supply, which is about 160A, so that should be enough for at least 50 odd RPi4's :)

It will take me quite some time to collect them and 52pi towers. I already have a "strange" cabnet layout planed for them mounting each RPi at 45 degree angle to help create convection air flow (maybe tower fans will help too) and eases cable connection and management. The RPi's are mounted on racks sort of like a shoe holder or plate holder from a dishwasher, and these can be stacked above each other. (overall heat management is an issue with tightly packed RPi4's - hence the "strange" cabnet).

I am going to use a combination of ways to allow each unit to connect to a master, controllers and the network, GPIO, serial TTY, 1Gb, WiFi and USB3 "null" (data only) cable (which use the same drivers as the ClusterHat x4 RPi Zero uses). I may even try 2.5Gb and/or 5Gb gear if I can afford it (but that might be restricted to CM4 devices). I might be able to make a ring network over USB3 cables, depends what needs to go along it, and how many hops it is, as to wheather it is practical (and every hop device will need to be on all the time).

I recently saw a way to connect multiple Host devices (PC + MacMini) to a single USB-C hub that shares devices, but I need to investigate that further (it might have been a Thunderbolt connection). Either way, I need some low bandwidth poll and control connections, a highspeed way to direct access shared drives, and seperate pipes out to internet for user VM style view/management and another to a gateway server with frontend management (so no inbound internet connections).

At the extreme end of the spectrum, I am considering adding an AMD box with multiple multi-HDMI capture devices, but I might have to wait for sponsorship for that one :)

The ability to swap or chop and change their network interconnectivity and 2x board locations allows me to create some flexible senarios. eg build farm, vm farm, docker farm, and a mix of any. When I have that flexibility, I'll make its operation available publicly somehow (depends on bandwidth atm).