Auto power circuit for an arcade machine

Some of the pinball machines which [Jeri Ellsworth] has restored have ended up in the break room at her work. We’re sure her coworkers are thankful for this, but sometimes they forget to turn off the power to the machines, and letting them run constantly means more frequent servicing will be necessary. She set out to fix the situation by building a circuit that will automatically power the machines.

We think the solution adds some much needed functionality. Instead of hunting for the power switch, you can now power the machine up by hitting the left flipper, and it will automatically shut off after about five minutes of not having that flipper button pressed. For this she grabbed a 555 timer chip and built a circuit to control the relay switching the mains power.

She added a magnet and reed switch to the left flipper switch assembly to control her add-on circuit. It connects to the base of a PNP transistor which controls a resistor network and capacitor. This part of the circuit (seen to the left of the 555 in the schematic) allows the timer to be re-triggered. That is, every time you press the flipper the 555 will reset the timer. Don’t miss the demo she filmed after the break.

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USB killswitch turns off your home entertainment bling automatically

Finally, the USB port on the back of your television can be tapped for something useful. [Don] is using this add-on device to automatically cut the power to his Ambilight clone. Initially, he got tired of unplugging the power adapter each time he shut off the television, so he added a switch. But laziness overcame him and he decided he needed an automatic method. After probing around on the connections available, he established that the serial interface (normally used for servicing the device) was not of any use, but the USB port is. He measured the voltage of the power bus to be 5V when the TV is on, and 0.15V when it is off. He whipped up the circuit you see above which uses the USB connection to trigger a relay, connecting power to his Ambilight clone when the television comes on, and disconnecting it when the set is switched off.

Our dream has always been an XBMC capable device that can Velcro to the back of a TV, and be powered from that USB port. Unfortunately the Beagle Board hasn’t yet made it to a stable level when running XBMC. Our next hope is the AppleTV 2, which can run XBMC but would require some hacking to get it working off of the USB port, raising concerns about how much current it would draw at 5V.

Magellan GPS hack for hassle-free charging

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Hackaday reader [Paul] recently shared a simple hack he put together via our Flickr photostream.

It seems that his Magellan GPS unit is pretty finicky when it comes to power supplies. When connected to the Magellan adapter, the GPS unit charged as you would expect. When connected to a PC, it sensed the connection and allowed its file system to be mounted, just as it was intended to do.

However, a problem arose when he tried hooking the Magellan up to a different power supply. The unit still thought it was connected to a PC, and refused to perform any GPS-related functions since its file system was tied up. Not wanting to lug around multiple chargers, he decided to see what the heck was going on with his GPS unit.

He pulled the plug apart and found that the 4th and 5th pins of the USB cable were shorted together. While most devices ignore the 4th pin, the Magellan checks to see if that pin is grounded. If so, it assumes it is connected to its power supply. If not, it assumes that it should act as if it is connected to a PC.

With this information in hand, [Paul] did the same thing as any of us would and hacked together a USB cable with shorted pins. The cable can be attached to any standard USB port or charger, saving him from having to lug around an extra adapter.

Everything You Need to Know About Wall Warts

If you work with electronics at any skill level you need juice. [Jon] has a great, and clearly worded tutorial about Wall Wart Power Supplies with pretty much everything you need to know about those little black boxes hanging off of your outlets.

The whole thing starts off with the basics like transformers, rectification smoothing and regulation, then moves on to the different basic types, dedicating a page to linear, regulated and switching types, giving output performance charts under different situations.

Also included is a run-down of DC barrel jack structure so you get the right plug every time, wall wart type identification, a random sample comparison test, and a good selection of formulas to even keep the old hats reading along. Although you might want to set aside a little time at 9 pages and some Q/A in the comments, it might take a moment to read.

Mini SATA power adapter does away with HDD docking stations

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[Marc] is pretty unsatisfied with hard drive docking stations as a whole. He says they are typically slow and unreliable, causing him all sorts of grief while he is troubleshooting a questionable hard drive. He decided to take some of the mystery out of the troubleshooting equation and built a standalone SATA power module.

Aware that SATA drives require 5v and 12v for operation, he disassembled one of his docking stations to see how it provided both voltages. He discovered that it used a simple PWM buck converter and decided to replicate it in the smallest space possible. His plan was to use a standard 12v wall wart to power the circuit, passing that 12v straight to the drive. A simple voltage step-down circuit would be built to provide the required 5v.

[Marc] reports that the power adapter is performing nicely, and he is quite happy with the size as well. He says that one major benefit of this sort of adapter is that it can be used to power any SATA drive, not just hard drives. He does mention that if he built another one, he might consider regulating the 12v output as well, so that he can power the adapter with a laptop power supply instead of a separate dedicated wall wart.

Grinding down your computer to just 8.5 watts

What can you do to make sure your system is running as efficiently as possible? Take a page out of [Mux’s] book, who went to great lengths to measure and adjust his system for ultimate efficiency (translated). What he ended up with is 8.5 Watts of consumption at idle and about 50 Watts under load. Luckily he posted a six-part series with all of the details.

Some of the changes he made were in software, like reducing voltage to certain hardware by adjusting BIOS settings, and installing display drivers that put the screen into the proper sleep mode. Others were hardware changes like swapping out the power supply with a hacked PicoPSU and removing unnecessary parts from the motherboard like the MAX232 com-port chip. Looks like we need to audit our always-on MythTV box and see if we can apply any of these power-saving techniques.

[Thanks Gijs]

Jumbo Size New Years Countdown

New Years celebrations tend to get bigger and bigger every year for most people, and [Brian] takes no exception. In order to top his lighted tree of a few years ago, he has concocted a 40’x40′ set of Seven-Segment displays made out of Christmas lights, hung from nearby trees. These displays would start counting down the minutes an hour before the ball drop, and be synchronized with music. Also in the spirit of a New Years party, the music he has chosen is in the form of a Power hour. The control board [Brian] is using also comes with two extra outputs, which he plans to use for the most exciting possible additions: Fireworks and Flamethrowers.

Be sure to check back after New Years to see a video of the device in action. Be sure to Hack, Drink, and Party Responsibly out there.