Modulab

Modulab aims to create an open hardware and software ecosystem for a modular homelab system. The cards should be capable of implementing common laboratory functionality (power supplies, scopes, etc), and they should be easy to create and integrate into the rest of the system.

Architecture

The Modulab system consists of 3 types of objects:

• A Core Module, of which there is one.
• A Backplane.
• Cards, of which there can be many.

Core Module

The Core Module is responsible for the following:

• Providing ethernet connectivity to the end-user device (PC or laptop typically).
• Serving the main web app to the end-user device.
• Handling Card identification.
• Providing power to the rest of the system.
• Providing I2C connectivity to the end-user device.

Backplane

The Backplane provides distribution of communication lines and power. Ideally, simple forms of backplane would only require an ethernet switch IC and nothing else. But the Core Module connector is capable of also transmitting a SPI connection, to connect to a Backplane controller IC. This can be used for advanced features, such as soft-start of cards.

Cards

Cards provide user functionality to the system. Cards have multiple different ways to communicate with the end-user device:

• Via ethernet.
• Via I2C.
• None :) A Card does not have to implement any communication if it's all self-contained.

Via the Backplane, a Card gets access to the following resources:

• 3V3, up to 6A shared between all Cards.
• 5V, up to 6A shared between all Cards.
• 36V, up to 5A shared between all Cards.

A Card is required to identify itself to the Core Module. The most basic ID is pulling the ID line high, to indicate presence. Further ID is achieved by having a Microchip UNI/O single-wire EEPROM connected to the ID line, through which extra information can be attained.

Connectors

All connectors used for the Modulab system are 2x30, 2.54 mm pin header format. Canonical implementations will use the Samtec LS2 connectors.

Core Module Pinout

Pin #	Side A		Side B
1	+36	144 - 180 W (4 - 5 A)	+36	144 - 180 W (4 - 5 A)
2	+36	144 - 180 W (4 - 5 A)	+36	144 - 180 W (4 - 5 A)
3	GND		+3.3	19.8 W (6 A) shared
4	GND		+3.3	19.8 W (6 A) shared
5	GND		+3.3	19.8 W (6 A) shared
6	GND		+5	30 W (6 A) shared
7	GND		+5	30 W (6 A) shared
8	GND		+5	30 W (6 A) shared
9	GND		GND
10	GND		GND
11	I2C_SDA	Shared bus	JTDI/NC	Programming
12	I2C_SCK	Shared bus	JTMS/SWDIO	Programming
13	GND		JCLK/SWCLK	Programming
14	DET0/BP_SCLK	Card detection/ Backplane SPI SCLK	SRST	Programming
15	DET1/BP_MOSI	Card detection/ Backplane SPI MOSI	JTDO/SWO	Programming
16	DET2/BP_MISO	Card detection/ Backplane SPI MISO	JTRST/NC	Programming
17	DET3/BP_SS0	Card detection/ Backplane SPI SS0	VCP_RX	Programming
18	DET4/BP_SS1	Card detection/ Backplane SPI SS1	VCP_TX	Programming
19	DET5/BP_CTRL_RESET	Card detection/ Backplane copro RESET	GND
20	DET6/BP_NC	Card detection/ NC if Backplane SPI	GND
21	GND		ETH_TX_P/ ETH_BI_DA_P	Ethernet TX; BI_DA+ in 1G
22	GND		ETH_TX_N/ ETH_BI_DA_N	Ethernet TX; BI_DA- in 1G
23	ETH_RX_P/ ETH_BI_DB_P	Ethernet, RX; BI_DB+ in 1G	GND
24	ETH_RX_N/ ETH_BI_DB_N	Ethernet, RX; BI_DB- in 1G	GND
25	GND		NC/ETH_BI_DC_P	NC if 10/100 eth; BI_DC+ in 1G
26	GND		NC/ETH_BI_DC_N	NC if 10/100 eth; BI_DC- in 1G
27	NC/ETH_BI_DD_P	NC if 10/100 eth; BI_DD+ in 1G	GND
28	NC/ETH_BI_DD_N	NC if 10/100 eth; BI_DD- in 1G	GND
29	GND		GND
30	RSVD	Reserved for future	RSVD	Reserved for future

Card Pinout

Pin #	Side A		Side B
1	+36	144 - 180 W (4 - 5 A)	+36	144 - 180 W (4 - 5 A)
2	+36	144 - 180 W (4 - 5 A)	+36	144 - 180 W (4 - 5 A)
3	GND		+3.3	19.8 W (6 A) shared
4	GND		+3.3	19.8 W (6 A) shared
5	GND		+3.3	19.8 W (6 A) shared
6	GND		+5	30 W (6 A) shared
7	GND		+5	30 W (6 A) shared
8	GND		+5	30 W (6 A) shared
9	GND		GND
10	GND		GND
11	I2C_SDA	Shared bus	JTDI/NC	Programming
12	I2C_SCK	Shared bus	JTMS/SWDIO	Programming
13	GND		JCLK/SWCLK	Programming
14	DET_IO	Detection/UNI-O signal output.	SRST	Programming
15	ID_0	Slot ID, bit 0	JTDO/SWO	Programming
16	ID_1	Slot ID, bit 1	JTRST/NC	Programming
17	ID_2	Slot ID, bit 2	VCP_RX	Programming
18	ID_3	Slot ID, bit 3	VCP_TX	Programming
19	CONNECTED	Connect to pull-up via 3V3.	GND
20	RSVD	Reserved for future	GND
21	GND		ETH_TX_P/ ETH_BI_DA_P	Ethernet TX; BI_DA+ in 1G
22	GND		ETH_TX_N/ ETH_BI_DA_N	Ethernet TX; BI_DA- in 1G
23	ETH_RX_P/ ETH_BI_DB_P	Ethernet, RX; BI_DB+ in 1G	GND
24	ETH_RX_N/ ETH_BI_DB_N	Ethernet, RX; BI_DB- in 1G	GND
25	GND		NC/ETH_BI_DC_P	NC if 10/100 eth; BI_DC+ in 1G
26	GND		NC/ETH_BI_DC_N	NC if 10/100 eth; BI_DC- in 1G
27	NC/ETH_BI_DD_P	NC if 10/100 eth; BI_DD+ in 1G	GND
28	NC/ETH_BI_DD_N	NC if 10/100 eth; BI_DD- in 1G	GND
29	GND		GND
30	RSVD	Reserved for future	RSVD	Reserved for future

Concious Design Decisions

Using ethernet over USB or some such. USB is fun and all, but implementing proper marketable USB devices requires that you worry about Vendor and Product IDs. So right from that angle, USB becomes a headache.

I also find it easier to reason about ethernet connections, since UDP and TCP are easy. Whereas dealing with USB is likely to be more complicated.

Both require a switch IC on the backplane. So from that perspective, the difference isn't that big.