How-To: Add USB power to your alarm clock

Your machine is modded out. It's got plexi hard drive windows, silent fans ,and it's half refrigerator. The other appliances are starting to get jealous and it's time to even the score. In today's How-To, we're modding an innocent alarm clock to provide five fine volts of USB juice right on the nightstand. Perfect for a bed-side USB fan on those steamy summer nights, a cheeky USB lava lamp, or, erm, a USB massager. Check it out.

For today's How-To, you'll need:

• USB port (Mouser Electronics 538-67329-0031)
  
• LM7805 power regulator (Radioshack or Mouser)
  
• Heat shrink tubing (or electrical tape)
  
• Multimeter
• Soldering iron
• Hot glue gun
• Screwdriver

To add our USB power port, we'll steal some DC voltage from the clock. We are going to run power through a LM 7805 voltage regulator to take it down to 5 volts. Adding a 220uF capacitor between the output and the ground can help smooth out the voltage if that's a concern. We referenced the USB pinout page at pinouts.ru and the data sheet for the LM7805.

Unsurprisingly, all the terminals are on the bottom of the PC board. The buttons on the side pop out, and a final screw holds down the board. The radio tuning hardware was pretty easy to align on ours, but be wary of more delicate designs.

With the board out, we cleared the area of conductors and plugged in the clock. If you're worried about the small exposed terminals carrying AC voltage, place some electrical tape over them before starting. We located 9 volts DC on the board at TP10 and TP11 (test pads). These were our favorite locations because they have nice big solder pads.

Soldering leads to the pads is pretty easy. Just heat up the wire and the pad and apply a bit of fresh solder.

Once the power leads are soldered on, re-install the PC board and run the wires through a good location. We brought them out next to the LED display.

Before finishing up, we did a quick test of the power setup. Flawless victory.

Deciding where to place the USB port depends on what you plan to do with it. Mounting it on the top is the most convenient location. There's plenty of room below for the port, and it'll give our USB light the most reach.

Dremel tools are great, but sometimes the quick, dirty (and stinky) approach is the easiest. We melted the hole with our soldering iron. Watch out for the fumes, but it gets the job done.

Test fit the port once the hole is cut. When you're happy with it, you can clean up the melty edges with some diagonal cutters or a utility knife.

Set the top of the clock down on a working surface (that can get hot glue on it). When the port is aligned, squirt in some hot glue to lock it down. You want to build up the glue for strength so take your time and let the glue cool down before adding more.

Once the socket is secure, solder on some leads to pins 1 and 4 once the socket is secure . Then follow up with some more hot glue. We waited until after the leads were soldered to add glue to the terminal side of the connector. The clear glue is still cooling off.

Match up the ground leads from the clock and the usb port. Slide some heat shrink tubing over them and

solder them to the center connector of the 7805. You might want to double check the polarity of the wires with your meter before soldering. Since we used two red wires, we marked ours with a black sharpie.

Wire up the other two connectors the same way. Positive power from the clock goes to the input pin and output connects to pin 1 of the USB port. If you're thinking of using the port to charge a low power device, you should consider adding a 220uF capacitor between the output and ground pins of the regulator.

If the 7805 was going to carry a lot current, we'd add a heat sink to the tab. In this case it'll be a light load, so we screwed it down with the PC board mounting screw. The tab is also a ground, so be careful that it won't short on anything. We had plenty of clearance. If you're worried, a bit of tape of heat shrink tubing over the tab is cheap insurance.

The hardest part of the project was putting the case back together. The speaker is pressure fit against the top with a spring,  the switches all need to be properly aligned, and you have to watch out for your added wiring.

Success! The small switch built into the light turns it on and off. As a bonus, the light can run off the backup 9 volt battery in the clock. During a power outage, we'd at least have a little light to find the flashlight with. It's great for low power devices like the LED light. If you're thinking of putting a USB port in your clock to charge up your portable brain, we'd suggest installing a small power adapter or regulating and tapping reduced AC voltage from the transformer inside the clock to avoid drawing too much power off the circuitry in the clock. Enjoy!

[idle @ Jun 13th 2006 3:17PM]

Cool.

I'm gonna put a USB clock on my.... hey wait a minute.

[Gr1zz @ Jun 13th 2006 3:19PM]

Sweet, i need to do this to my cars dash rather than using up the cigarett lighter.

[Sunil @ Jun 13th 2006 4:10PM]

As an owner of the exact same alarm clock, and as an avid Engadget reader, I feel obligated to make this mod.

Unfortunately, you lost me at "LM7805 power regulator." This may be a little out of my scope...

[Yardsale @ Jun 13th 2006 4:12PM]

I have that exact same clock too, but like most other DIY how-to on the interwebs, it goes over my head :(

[genexk @ Jun 13th 2006 4:17PM]

what happens if i need to reboot my computer?

[Grant Ewert @ Jun 13th 2006 4:24PM]

That looks cool. Does anyone know where to get that little usb port?

[chris @ Jun 13th 2006 4:47PM]

genexk, this isn't to POWER the clock, this is to power things FROM your clock. you will not be plugging you clock into a PC. on second though, nevermind. this this mod isn't for you.

[manny @ Jun 13th 2006 4:49PM]

it would be nice if you can plug in a flash drive and have the clock download torrents to it overnight...maybe add another usb port to add wifi?

these mods are so awesome!

too bad i fried my xbox mainboard trying to mod it :

[Andrew Rahimi @ Jun 13th 2006 4:50PM]

Interesting idea. I'm thinking of using this to power my iPod while I have it connected to the speakers on my bedposts. Does anyone know of a cable where one end is an iPod dock connecter and the other end splits into both usb and line out/headphones? That way I could have one connection for both power and audio out, plus the geekiness of plugging my iPod into a 10 year old alarm clock only to have the sound come out from somewhere else.

[Will O'Brien @ Jun 13th 2006 4:55PM]

I added a part number for a usb port from mouser.
It's a type 'A' pcb mount recepticle.

[asdfasdf @ Jun 13th 2006 5:52PM]

what soldering iron is that? its tip is so thin! i love it!

[Eric @ Jun 13th 2006 6:28PM]

that's weird...I've owned that alarm clock since 1992...literally...and still use it today. As for the usb mod...no thanks.

[Will O'Brien @ Jun 13th 2006 6:52PM]

It's a 15 watt weller.

[iGotNoTime @ Jun 13th 2006 7:28PM]

Would be great for those little flash MP3 dirves that charge on USB power!

[Sir.Pinkerton @ Jun 13th 2006 7:55PM]

Andrew,

Check out either the SiK din, or the SendStation PocketDock Line Out USB. The PocketDock comes with audio cables, but the din doesn't. Or you could just get one of Apple's docks. Heh.

[Lan Rat @ Jun 13th 2006 8:09PM]

Or... i just put my hole ipod charger in my clock. it works with my ipod, and any other usb item.

[ebob9 @ Jun 13th 2006 8:57PM]

I don't think this would charge my Blackberry 8700, or i'd be all over it. Stupid Blackberry and "Needing special USB drivers for propritary power".

[sdonham @ Jun 13th 2006 11:46PM]

You don't need drivers for the Blackberry 8700 usb power. I thought you did too, but I tried the usb-altoids tin charger on my 8700 and it worked like a charm.
http://www.instructables.com/ex/i/1686FF3E41011029AC23001143E7E506/

[ant101 @ Jun 14th 2006 2:23AM]

err... someone mentioned doing this to your car?? DON'T
The electrics of your car is not the same as your beloved alarm clock! In short, the voltage on your car varies greatly, and more components are needed to ensure that you don't fry the LM7805 , or even worst your ipod!!

Great article!

[mark @ Jun 14th 2006 6:19AM]

With the Blackberry, it probably just needs drivers to charge from your computer. Until the device is recognise on your PC, it can only get 100mA... not enough to charge. But once its enumerated, it can get half an amp. Thats the reason it needs drivers, but if you can just give it the current it wants, it will charge.

[Juttin @ Jun 14th 2006 9:36AM]

I actually put a USB port in my car just last week. I used a mod that I found somewhere for creating a usb port from a cell phone charger and installed a lighter plug in that tapped into power that is only live when the ignition is on. I put it all behing the center dash and dremeled a hole in the plastic area to the right of my CD player. It works great. The key is using a cell phone charger with 5v output and hiding everything behind the dash

[Jason @ Jun 14th 2006 9:50AM]

Nice modd, but not that nifty cause it's only about power supplies...why not find a 9v nightlamp and connect it directly.

[or just buy a flashlight :)]

[gio @ Jun 14th 2006 11:31AM]

As I'm looking at these pics, co-workers are walking by looking at my screen like I'm a bomb terrorist.

[John Laur @ Jun 14th 2006 1:58PM]

If you are going to do this mod, you need to realize a couple of things that the author does not seem to worry with (although he mentions both but sort of dismisses them). The LM7805 (and compatible) are linear mode regulators. They dispense with the extra voltage as heat. The maximum current that any USB device (should) draw is 500mA which is well within the range of what they are usually rated to handle.

The problems is that you really do need decoupling capacitors to protect your electronics and to avoid shorting the DC inside your clock, and you also need a heatsink even at 500mA.

Furthermore, some of these cheap USB-only-for-power things will happily draw as much current as they want from the port. Computer USB chipsets have current limiting circuitry on them to never allow mor than 500mA out but obviously the LM7805 has none.

If you want to trust your cheapo USB phone charger not to short or set fire to the LM7085 inside your radio, fine by me, but a couple of caps and a heatsink isn't a significant expense for this.

An "upgrade" would be to move to a switchmode regulator which helps the heat problem significantly and also draws a little less power too (not that it's a big concern).

[Will O'Brien @ Jun 14th 2006 3:29PM]

Thanks for the comment.

The post states that you should consider adding a capacitor to smooth out the voltage and points out that you should add a heat sink for higher draw applications. For serious apps, adding a seperate power supply and tapping the AC (before or after the transformer) is the way to go.

We're driving a LED with the thing - Very low current draw (like 25 to 50ma) No prolem for a 1.5amp rated lm7805 without a heat sink.

Your comment should help clarify issues for people with questions.

[Alan @ Jul 9th 2006 7:22AM]

it would be nice to modifily the usb light to have software control on/off.. I wish I can do that :(

[Ben @ Jul 20th 2006 10:18AM]

You should add at least 2 100nF decoupling capacitors between 9Vin and the center pin and center pin and 5V out. Without these componets and long leads the LM7805 will probable ossilate and therefore get very hot.

Another thing to remember is that you are taking power from the clock supply 500mA would probable cook your clock as well as anything connected to it. You would be better off buying a cheep powered usb hub and then pluging in anything usb into this.

Ben

[usb-review @ Jul 27th 2006 10:57PM]

That's fantastic, you should try it on a few more home appliances. Thanks.

[John @ Sep 13th 2006 6:56PM]

Actually, USB devices will not indiscriminately draw current, depending on current-limiting in the computer USB port. This is not true, except in the case of a broken device.

In fact, USB devices must only draw a maximum of 100mA UNLESS and UNTIL they negotiate with the host controller to draw up to 500mA as a "high-current" device type. Therefore, it's a pretty good bet that any device you plug into it will draw 100mA or less (because it has nothing to negotiate with for more).

Heat sinks are always a good idea. Just dropping 9V to 5V at 100mA will generate ~0.5W of heat. This can build up the temperature inside a closed container and derate the current-handling ability of your 1.5A regulator! I get a finned heat sink, drill a mounting hole and three wire holes, and mount the entire heat sink + regulator on the outside (usually in back) so that the heat stays outside.

[Bobmark @ Oct 8th 2007 3:52PM]

There's an easier way - just use http://onlineclock.net

The USB is already built-in ! For lazy slobs like me. Still, if I had the time...

[slack-jawed-yokel @ Jan 18th 2008 6:45AM]

I have that clock as well. Interestingly, Neo from 'The Matrix', also had that very same alarm clock in the opening scenes of the movie.

[Simon @ Aug 7th 2008 10:23AM]

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