vxo, 26 days ago

In case you're wondering how these worked without an isolation transformer, the secret is in the "Silicon DAA" design. Everything on the phone line side of the modem is powered only by the DC voltage on the line. Serial data communication back to the PCI interface chip is passed via the seemingly random value 2KV rated ceramic disc capacitors.

In case you are wondering if this worked at all: yes, in most cases.

In case you are wondering if this was any good: lol NO

ceramic disc capacitors for data transmission

recursive, 26 days ago

@vxo That's kind of brilliant cost reduction, though I do have questions about the signal integrity :)

I guess they're just holding the line off-hook with those SOT-23 transistors? I don't see anything like a relay