Month: August 2010
I have an LG Lotus phone. It charges over a USB cable, which plugs into a USB-like port on the charger. I recently wanted to be able to charge my phone in the woods of Vermont, where outlets to plug a charger into are few and far between. To fix this, I built a simple regulator that draws power from a 7.2V RC car battery and provides 5V DC to a USB jack.
Unfortunately, when I plugged my phone into it, the phone displayed a message that said “Please use only genuine LJ accessories”.
To figure out how the phone identified the charger, I opened the charger up. I had visions of LG using an I2C EEPROM to store a unique identifier or some sort of crypto chip performing a handshake with the phone based on a shared secret that was baked in at the factory.
In reality, it’s nothing that complicated. The data lines of the USB port are connected to each other. This means that anything the phone sends down one data line will show back up on the other one, so it can detect the connected pins by driving one line high and seeing if the other line also goes high. I connected the data pins on my homebrew charger, and the phone started charging from it.
The Rhode Island Maker Faire, which I will be presenting at, is looking for a few kind souls to pledge financial support. Help your local DIY crowd and encourage innovation and tinkering!
This evening, I added heat sinks to a couple of rectifiers that I’m planning to use in the power supply of a DIY plasma cutter. The rectifiers will each be handling half of the power load of the device, so I have beefy 35A/600V rectifiers. Each rectifier has a square metal case with a hole in the middle, so I drilled and tapped a hole in a the centers of a pair of CPU heat sinks and bolted the rectifiers to the heat sinks. This picture may help to make the assembly clear.
I had high hopes for the original fans that were on those heat sinks, but the lubricant that was in them had turned to gum, and so they didn’t spin. The new fans are from laptops, and run on 5V.
I’m planning to get the 5V from the low voltage filament windings of the microwave oven transformers that I’m using for the isolation transformer of the power supply. There are two sets of two transformers, wired “back-to-back” to act as isolation transformers. I’m going to post a complete schematic as soon as the power supply section of the cutter is fully assembled.
I just applied to exhibit at the RI Maker Mini-Faire. This is kind of a last-minute thing, so I’ll just be showing Cnidaria Hallucingena and whatever I have done of the various projects kicking around the house. I should probably also get business cards together by then, but having them done in 10 days strikes me as unlikely.
The Faire is August 28, 2010, at the Bank of America Skating Center in Providence RI from 3pm-11pm.
UPDATE: I’m in!