Portable Voltage Regulator

Powering small equipment

Close-up of circuit diagram and formula

Close-up of board

Close-up of board and battery compartment

Setting voltage requires a jeweler’s screwdriver and multimeter

Setting voltage requires a jeweler’s screwdriver and multimeter

Setting voltage requires a jeweler’s screwdriver and multimeter

Close-up of case with battery removed

This entire project was made from recycled materials, so nothing new was purchased to create it. I just looked through the random ICs I had and built a circuit around one of them.  This uses a voltage regulating transistor and a pair of resistors (circuit diagram is sharpied onto the inside of the tin) that control the output voltage down to the thousandth of a volt. The formula for the ratio of the two resistances is also scrawled onto the bottom left of the tin, but I have to admit I didn’t use it because it was easier just to balance out the resistors with a jeweler’s screwdriver and then test the resistances with a multimeter. Lazy, I know, but I’m not a mathematician.

The output maximum is roughly 1 volt lower than the maximum input, so 8 volt max out for 9v in, and the minimum is in the micro-volt range.

Tested and works great at recharging a cellphone, just don’t adjust the voltages “while” you’re charging a device because there isn’t currently a way to tell that the voltage is too high and it will send a voltage surge through the USB that your device may not be protected against. Also be aware that some devices are power hogs and will require more amperage than a 9 volt battery can produce through the LM317T.

Future improvements:  clean up wire traces on back of circuit board, add a switch, and add ability to use multiple power sources (option to use AA or 9v, for example).

The last photograph is of a separate project where I essentially “cheated” by disassembling a USB car adapter/charger and attached the power input to a 9v battery and the output to a USB port. The form factor is much smaller and it was designed by someone who just does this all day, so I trust it. Just be mindful that the amperage will be lower than you might desire, so if you decide to take apart a car adapter, choose one with a high amperage rating.

-Brandon

Add a USB port to your WRT54Gv4

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Chip designer have to think broadly if they want their product to be profitable. Often, they include features in their chips that aren’t implemented in a final product because they’re cost prohibitive or aren’t necessary. So when Linksys was forced to publish their API because they used software that was part of the GPL, that gave hackers full access to all the hardware in their products. Software like dd-wrt, OpenWrt, and others, added new features to the routers by replacing the proprietary and inaccessible firmware (the operating system running on the router) with open-source firmware.

A wonderful walk-through that is almost a perfect analog for this post is Void Main’s wiki article on USB modding a WRT54Gv3.

After installing dd-wrt on my router and confirming that it’s chipset ( Broadcom BCM5352) has an on-board USB 2.0 controller, I loosely followed this article to break out a single USB port (I felt two wasn’t necessary for a git server). USB is driven by a clean 5V DC power source, and the router is driven by a 12v DC ~1A power supply, so I built a circuit around a 7805 5V regulator that I pulled out of a stereo, some filtering capacitors and resistors to comply with the USB standard, and tapped the USB hub on the BCM5352 for the USB + and – channels. After that, I followed this walk-through to setup git on the router and ensure the files were kept on a thumb drive and not in local memory (which is 16MB and nowhere near large enough for file sharing).

Unfortunately, this project was done with time constraints because it did need to be implemented same-day to host files, so the photo documentation was sparse and is not exactly linear. Please post any questions you have and I’ll do my best to answer them.

There are hints on this process all over the place :

7805 USB power circuit

Evidence of a USB controller

Linksys WRT54Gv2 USB mod