Spoofing a laptop charger checker

klugesmith, Wed Mar 07 2018, 07:01AM

My Dell laptop PC moves almost daily between different places, each with its own charger. One has a scrounged HP charger, whose voltage and power and connector are identical to ones from Dell. It was a nuisance to see:

That's the laptop disparaging a power supply whose brand is "wrong".

These power connectors have three contacts: metal barrel outside, metal barrel inside, and center pin. The center connection goes to a power supply ID ROM, in 3-pin TO-92 package, using a 1-wire serial protocol invented for such things. It makes sense that when a laptop model wants a 90 watt PS and finds a 60 watt PS, it might slow down & not charge the battery. It's sad when it does that for someone else's 90 watt PS, which might be identical except for the label sticker and machine-readable ID.

No problem. I made a spoofing extension cord, grafting a power input connector from ebay onto the output cable from a dead 90 watt Dell PS. Including just enough of the circuit board to get the ID ROM (and, as it happened, an LED and a RF choke).



Now the computer thinks the charger is by Dell: