Pocket USB Emergency Charger





Introduction: Pocket USB Emergency Charger

About: Electronics hobbyist and a DIYer and i love doing this stuff.

I been able to make a Pocket Emergency Charger compatible for smartphones and other USB compliant devices out of salvaging an electronic pcb from an old cd player.,Since the famous LM 7805 Linear Regulator i found was the main component used to built a charger.i have seen various instructable project in various form here too.,So i must do a different design among others.

Objective: for emergency use only(while away from a wall socket ),for charging USB compliant device when they run out of juice as your powerbank runs out of juice too.Buying a spare 9 volt battery would be the best remedy that can be access in stores nearest to you.

*Steps and how i made it were all explained here.

Step 1: Materials and Tools Needed

1. LM 7805 (salvaged from old cd player)

2. 3 Resistors 100 ohm (salvaged from old cd player)

3. Heat sink (salvaged from old cd player)OPTIONAL ONLY

4. Some Wires

5. SPST switch

6. Flexiglass 2.5 mm thickness( i used scrap only)

7. 9 volt battery(6F-22)

8. 9 volt battery adapter (from an old 9v battery)

9. LED ( any color)

10. USB-A Female

11. PCB


Soldering Iron (30w)

Soldering Lead

Analog Multitester ( i don't have Digital Multimeter yet)

Helping Hand (optional)

Ruler,Pencil,scratch pad paper( i used old bond paper with print on it)

Scoring Blade( use for cutting Flexiglass)

Vinyl tile (i used scrap only)

Quick Dry Epoxy (mighty bond)

Elmers glue( optional for patching gaps)

Step 2: Building the PCB

Soldering all the components needed together were quite and simple to follow as the schematics in image form explains it all.I just added 2 resistors to the D+ and D- terminals of the USB as apple products won't recognized it without those two resistors.

Step 3: Preparing the Bezel

The funnest part and the most challenging in doing this project is the "Cutting"...So i must do a simple draft (plan) to fit all the components inside it and to see how big or small it would end up eventually.Using a thinner size flexiglass would make it smaller(around 5mm smaller than this)..I suggest using 1-1.5 mm flexiglass commonly found on a used transparent cd case is the practical way of building the bezel.And it gets more fun when i get confused with the battery dimensions found in googling only..So i rush myself to purchase an Extra Heavy Duty 6F-22 Battery made of carbon zinc,i can't find an Alkaline at the time of buying it in store.Then i measured it manually to get the most accurate measurement for my project.The image attached of 9V battery dimension are from different battery manufacturers.Which were all different from each other and to the battery i bought..And i found it confusing.

Step 4: Assembly

After several minnutes of cutting ang scraping,it's time to assemble it with the pcb chip inside.So after fitting and applying some adjustment of the flexiglass through scraping using exacto knife.,I glued first the front and rear part of the bezel,then the left and right part of the bezel followed it,And finally soldered the 9volt battery adapter on it's extended base.As seen on image,i put some holes on the bezel itself,three holes on each side and one underneath the base,hoping it would help the heatsink to cooldown itself when it heats up gained by LM 7805..

Step 5: Test and More Test

Run a test first on multitester not directly on any device,so if any problem and there is a short circuit,it wont hurt your device.And i did some errors on my first test,i found that the LM 7805 isn't working ,the multitester dc voltage result still showed me 9.2 volts DC,i wonder why,.,so i dismantled the left side of the bezel to check what's wrong..And i found what causing the LM 7805 did not work-the resistor soldered on the (D-) terminal is shorting with the Positive Input of the LM 7805,luckily the LM 7805 did not die easily after it shorted.And fix it immediately..And put some insulation that caused it,and run the test again..Finally,achieved the 5.1vdc required for charging USB devices.

Step 6: Paint Job

Spray painting it is just an option,but i still have left over of spray paint lying on my craft table..So i finished it with metallic black spray paint again.Patching or masking the USB and LED indicator part and the 9 volt battery adapter area.

Step 7: Result

Then another project was done out of salvaging electronic parts and using scrapped materials.That would be added to my DIY collection that i can used in times of need.

To anyone who is interested in doing this type of project,instead of using a common 9 volt Carbon Zinc battery

i suggest choosing the right 9 volt battery will be helpful ,as it will prolong charging time on your device.as the image shows types of 9 volt battery with their corresponding specs.

So there it goes again.,hoping you enjoyed reading it,and hoping to help someone who wants to build something like these,or just used the common and famous use of Altoid's tin case for casing and easy set up.The black tin case shown in image is used for storing my AA rechargeable batteries.

2 People Made This Project!


  • Creative Misuse Contest

    Creative Misuse Contest
  • Water Contest

    Water Contest
  • Oil Contest

    Oil Contest

25 Discussions


2 years ago

@yonatan upon checking your project link built last July 2015,clearly my project built last March 2015 showed they were both different in many things,the casing,source,size,built and materials.No offense,yet we both used the same component(salvaged LM7805)that doesnt mean we both have similar project.And your project doesnt even show a step by step procedures how you made it.,The zip you provided doesnt work either.


3 years ago

It gets more clear now,right i miss that part about rechargeable bat with 1.2 v/cell as i was thinking about the the ordinary carbon AA 1.5v/cell while typing.
I should try that MCP1826S too.,maybe on the next upgrade of this type of project...Anyways thank you for the inputs here.

15, 7:29 AM.jpg

3 years ago

As you were saying
"a typical battery is around 2500 mah where an AA is usually more like 500"how do you achieve that 2500 mah on a typical AA battery wired in series to make an output of 7.5vdc
-can you elaborate it?

15, 8:57 PM.jpg
1 reply

What I meant is that a 4 pack of AA is probably around the same $5 you're going to find a 9v for in an emergency situation, and that string of 4 will give you 6vdc@2500mAh, which is 15Wh (about 12.5Wh gets through the reg to your pack)

a 9v@600mAh is 5.4Wh, and 3Wh gets through the regulator to your pack.

I am assuming an LDO in this case, though, as 4xAA won't run a 7805

Also, that math is based on energizer's spec for standard Alkaline AA or 9V respectively, and the full capacity spec is at 25mA. The reality is that for both AA and 9V you're going to lose about 40% to heat if your phone's charge circuits are pulling 500mA or more. (It's apples-apples though, since they'll both have about the same loss)

@alex_skipp What type of 9volt battery did you used? as i mentioned choosing the right 9 volt battery would helped.I suggest using Lithium 9volt battery prolong charging time.

9V specs.jpg
7 replies

Another thing to keep in mind is that with most battery types, discharge rate also affects capacity.

Most phones these days are expecting about an amp of current. Accordign to energizer's datasheets, their standard 9V alkaline has a capacity of about 600mAh but only at a 25mA discharge rate. at 500mA discharge it fals to almost half (around 350mAh) Chances are you're getting even less when charging a phone.

As far as "lithium" goes: They're better in that regard, and their overall capacity is better, so you'll likely get about 50% charge into an average smartphone. Sounds pretty good, until you realize that they're >$20 a piece.

@ Arx As i'd mentioned using an alternative regulator would be an advantage,as you can see in the image in article step #7 - LM2940 or LM2940C as alternative to LM7805.and using a 9v typical carbon zinc,gave at least 25 % as i tested it(maybe depends on the brand you use)...as i keep on saying the objective of this project was for emergency only.Using a rechargeable AA battery (NiMh) would give better result,i thought about that.,then you have to bring two device then.One for this type of unit and one for 5 battery holder pack(if you use LM 2940) or 6 AA battery holder pack (for LM 7805).Or you can just make a bigger bezel to put all things together(the AA batteries plus the holders plus the pcb).And my purpose here was to build a different design(mentioned in Intro) and made it as compact as possible.Can you suggest other Linear Regulator as an alternative to LM 7805 aside from the one i mentioned here which was the LM2940 or LM 2940C? it would be great if you shared it here.i'll be waiting for your respond...thank you!

(typo correction)Using a rechargeable AA battery (NiMh) would give better result,i thought about that.,then you have to bring two device then.One for this type of unit and one for 4 AA battery holder pack(if you use LM 2940 requires at least 6v input) or 5AA battery holder pack (for LM 7805 requires at least 7.5volt dc input).Or you can just make a bigger bezel to put all things together(the AA batteries plus the holders plus the pcb)

Rechargable AA are only ~1.2V, so you would actually need 5 of them even for the lm2940, and 6 for a 7805. That's getting pretty impractical. 4xAA holders are quite common, and the square 2x2 type aren't even all that much bigger than a 9v. 5xAA are not common at all, 6xAA you could get, but it's getting pretty bulky by then.

Yeah, that regulator looks reasonable too. I was still thinking for "emergency" purposes, and a 4xAA battery holder for use with a pack of ordinary Alkaline AA. At a quick glance, an MCP1826S looks like a good regulator for the job. It has a typical dropout of 0.25V at 1A, so it would stay in regulation down to around 1.3v per cell. after it falls out of regulation, the phone will likely charge a little longer since they'll usually still run on slightly less than 5V. I expect you'll get the majority of the useful capacity from the AAs and probably get a full charge on the phone(or close, at least)

As you probably know, with linear regulators there's no "efficiency" to be concerned with. They'll all be dissipating the same amount of energy, the only difference being that they'll continue running to a slightly lower voltage. Using an LDO on a 9v is pointless, because by the time you're down to ~7v, the battery is pretty much dead anyway. The extra volt of room will make very little difference.

Also, with a LDO regulator, the input and output capacitors are much more important, and you should follow the datasheets so you don't end up making an oscillator. It's probably worth it if you're trying to run on a 6v supply, but if you're running off 9V anyway, the 7805 is tough to beat.

Personally, I would probably just do a boost regulator, and you could power it from a single AA. Obviously the complexity is way higher, though.

Then if you don't want to pay $20 for lithium battery,why not shift to a pack of Alkaline(12 pcs/pack for $17.95 found here:



This is the one i keep saying to use as an alternative to LM7805 as the data sheet image shows.(the LM 2940 or LM 2940C)

LM2940 specs.jpg

What would work tons better would be a low drop out 5v regulator, and 4 AA batteries.

that gives you 6V to work with, and you'll only be wasting about 17% of the energy instead of 44%

More importantly, a typical AA battery is around 2500mAh, where an AA is usually more like 500, and usually the cost is similar for a 4 pack of AA.

The AA should give you a full charge on an average smartphone, a 9v will be more like 20% at best.

You will need a low drop out reg, though. To use a 7805, you would need at least 5 AA, and the 5th will just go to dropout in the regulator (no benefit)

1 reply

I meant to say "where a 9V is more like 500mAh"

@fernandv,thank you for your suggestion and comment,i'll consider altering some components of it,when i got my LM 2940 from my supplier and plan to add capacitors for voltage output stability..

Hi, I like the way you made the housing.

The led current with the100 Ohm series resistor isabout 70mA. That is way too much for the led, and drains the battery innecessarily. I would suggest to put 1k instead.

Without a heatsink, the 7405 will heat up vary rapidly!


3 years ago

@mjHobby whats not practical in it?, most parts came from a salvaged pcb,which cost me nothing but effort.,anyway thanks!


3 years ago

@jdedge thank you!,having a heatsink was only an option,its better than to melt the entire flexiglass bezel without it.imo


3 years ago

@voblak,yes you are right,i just test it if it would work without it,i'll consider it next time.

15, 6:46 AM.jpg