Instructables
Picture of $3 Emergency Solar Radio

In honor of all my good friends still over in Japan I've decided to create an Instructable for a $3 Emergency Solar Radio. It's a great thing in case of tsunami, nuclear melt down, or zombie invasion. Plus it's really cute when put into an Altoids tin.

My plan is to send this as a (slightly) joke birthday gift to a good friend of mine living in California, who just so happens to be freaking out about possible nuclear clouds. This will also be really nice for her when she starts going camping again this summer.

The design is very simple and only takes about 45 minutes to put together, less if you know what you're doing.

If you'd rather not make one yourself, I'll probably be throwing up a couple completed ones as well as most of the parts over at my website BrownDogGadgets.com.

 
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Step 1: What you need

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I bought all the supplies I needed from my local $1 Store. (If in Japan, a 100 Yen store.)

To buy:
1x FM Radio
2x Solar Garden Light
1x Diode ($1 for 100 of them online, or take one out of any random junk pile)

If your local $1 Store isn't as cool as mine, you can probably find these things locally, online (like at my website BrownDogGadgets.com), or from a trash bin.

Tools:
Soldering Iron
Drill
Wire
Wire Strippers
Goggles
Tape

Optional:
Altoids Tin
Hot Glue
Mini Speakers ($1 Store, or take apart old headphones)

Support Me By Buying Some Parts...

If you can't find solar cells or cheap AAA batteries, I have quite a few on my website BrownDogGadgets.com. The same solar cells I use to make my Solar Cockroach would work great for this project. You could also slap on a bigger, more powerful cell onto the outside of the tin like these nice 4.5 volt cells.

I also some AAA battery holders and very cheap AAA batteries for sale that have a much higher capacity than the ones you'd find in your average solar light.

Step 2: Salvage The Solar Lights

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God bless the $1 Store and it's amazing Chinese junk. I found my local store selling these cheap plastic solar lights, and I ended up buying all of them. Why ask you would I spend $120 at the $1 Store?

Inside each of these lights is one 3.5 volt Solar Cell, one AAA NiMh battery, one LED, one transistor, and one resistor. That is honestly worth more than $1 when making projects. Plus I can always make runway light patterns across my backyard and see if anyone will try and land there.

If you can't find these solar lights, you can find them in bulk on ebay. You can also just use a couple of regular NiMh AAA batteries and any old solar cell 4 volts or above, but it will cost you a little bit more than $3.

Take apart the head of the solar light. Be careful to remove the little circuit board for future use.

Snip the wires going to the solar panel. Depending on your solar light you can either pry it out with a screw driver or push it from behind. I used a nail to push from the underside. The glue they use isn't very strong and the solar cell is quite sturdy.

The only danger is that you break off the little solder point on the solar cell. If you do this just throw it away and take apart another solar light.

After doing this to both lights you'll now have two solar cells and two AAA batteries.

Step 3: Test Your Radio

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Seriously, test your radio out ahead of time. Better you see if it's working now than after you take it apart.

You can also test out your AAA batteries to see if they're working and if they'll play nice with your radio.

Now you may notice those little white speakers, also from the dollar store. They suck more than the cold vacuum of space. I ended up not using them with this project and instead used them to entertain my cat.

Step 4: Take Apart Your Radio

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This part can be tricky depending on your radio. This is how I took apart mine.

I first unscrewed the back.

After that the only thing holding in the board was the volume nob. If you're lucky the top of your knob will come off (no pun intended). If you look at my board you'll see the "buttons" on my radio are nothing more than some common momentary switches. I even have a little LED there as well. Bonus!

Now the volume nob on my radio would not come off, so I took a different approach. Using some tin snippers I cut apart the plastic case until everything was free. Then I used some little wire clippers and cut the remaining bits away from the knob area. You should wear eye protection during this part as plastic was flying everywhere.

You'll notice that I saved the "Battery Holder" area. Do this as you can. You can just buy a AAA holder for $1, but we're on the cheap here people!

In the end you should have, if nothing else, your radio's circuit board out, and if you're lucky you'll have a battery holder as well.

Step 5: See If It Fits and Works

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My personal favorite case of choice is an old Altoids Tin. No matter what you're using to hold the project in, now is a good time to see if everything fits and that it still works fine.

Mine fit perfectly into the tin case. After hooking up some headphones everything seemed to work fine, including the LED.

This is also a good time to design your internal layout and decide if you have enough room to put the solar cells on the inside or not.

Step 6: To Speaker or Not To Speaker?

Picture of To Speaker or Not To Speaker?

My original plans were to solder in a little toggle switch and some speakers. This way the user could choose between using the internal speakers or extrernal headphones. This didn't work.

For one the little speakers I got from the $1 store sucked, hard. The FM radio didn't have enough power to get much sound out of them, then again neither did my iPod. This would be a really awesome thing to work it in there, maybe by finding some powerful little headphones or one really powerful little speaker. If you can't, I honestly wouldn't worry about it.

(Yes, I tried them out before removing their protective cases. It didn't make a difference. Thats $1 I'll never see again.)

Step 7: Drill Baby Drill

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So instead of doing internal speakers I just made a hole for the headphone jack.

To do this I first lined up everything inside, then marked where I wanted to drill on the outside.

Drilling Altoids tins is easy. Just be careful. Get a good RPM going, press some, and make sure your fingers are safe. You may want to file the inside of your tin if you've got lots of metal bits poking things. (I didn't, but you never know.)

It also doesn't hurt to have a backup tin around. Just in case.

Make sure your headphone jack goes all the way into the drilled hole! If nothing else test that your headphone will in fact work with how you've got it set up!

Step 8: Wire Up The Cells

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If you have a multi-meter test your solar cells out. The ones I used each put out between 3.3 - 3.5 volts.

These cells are great for charging up a single AAA battery of 1.2 volts, but now we're using two AAA batteries in a series for a total of 2.4 volts. Seeing as how the goal of this is to be an emergency radio and be able to charge up even in bad weather we should boost the voltage on our solar cells. (Or you can use any solar cell or group of cells that put out more than 4 volts that you have around.)

To do this we'll be connecting our cells in a series, which means the amps will stay the same but our voltage will double.

First, solder a long wire onto the diode end with the black strip. Then solder the other end of the diode to the positive tab of one of your solar cells.

Solder a long wire onto the negative tab of the OTHER solar cell.

Each cell should have one wire now. One positive (with a diode) and one negative.

Now connect the two cells using the two remaining soldering points, AKA bridge the remaining positive and negative solder points. I just used a bit of scrap wire, anything will do.

When you're finished use some tape to hold down the wires and to protect the solder points.

If you're at all confused just look at the pictures below.

Step 9: Wire Up The Cells and Battery Pack

Picture of Wire Up The Cells and Battery Pack

Now wire the positive and negative wires from the cells into your circuit.

You can either wire them directly to the board or to the battery pack. I choose to wire them directly to the battery pack area.

Positive to the positive tab, negative to the negative tab.

Sorry for the blurry photo, I didn't notice that until I starting writing.

Step 10: Tape It Up

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Once again, test it to see if it works. Use a multi-meter to see if power is flowing properly, or just put it in some sunlight and turn the radio on. Depending on how many amps your cells put out the radio should work, though if they're super cheap they might fall flat on directly powering your radio. That's ok, thats why we have batteries.

I used some double sided foam tape to secure everything inside. It keeps the circuit board from touching the metal tin area. If you're worried about shorts just put some electrical tape on the bottom of the tin.

Just be sure to line up your headphone jack and that inserting headphones doesn't unstick your circuit board.

Hot glue also works just fine.

Step 11: Finished!

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Everything fits into the Altoids tin and it easily shuts. Now I have a little radio that's solar charged and has a little LED. That wasn't so bad. It even gets a signal through the Altoids tin.

Plus in a pinch you can swap out the AAA batteries for regular ones OR use the solar cells to charge up other dead NiMh AAA Batteries you have.

Other Ideas that would be easy to do if you're willing to put in the time and parts.

1) Use a rechargeable 3V coin cell or ultra capacitor to save space.

2) Put solar cells on the outside, and speakers inside.

3) Work in some retractable headphones or some speakers.

4) Drill a hole for the LED to stick out the front and also have a button on the outside to work the LED. (if your radio has an LED like mine does. Or heck, wire in your own LED into the circuit.)

Support Me By Buying Some Parts...

If you can't find solar cells or cheap AAA batteries, I have quite a few on my website BrownDogGadgets.com. The same solar cells I use to make my Solar Cockroach would work great for this project. You could also slap on a bigger, more powerful cell onto the outside of the tin.

I also have some AAA battery holders and very cheap AAA batteries for sale that have a much higher capacity than the ones you'd find in your average solar light.

I also have a wide range fun fun little kits you can put together if you need a little weekend project.

Step 12: Version 2.0

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So I gave building one of these a second try and it worked out a bit better. This version is just like the old version, except on steroids and a bit more expensive.

I used another $1 Store Radio as well as managed to fit in some $1 headphones. Instead of using the $1 Store solar lights I instead used three 1.5 volt 50 ma solar cells which are smaller and more powerful. I also used some higher capacity AAA batteries I had.

The total cost of this one is about $6-7. Twice as much as the original one, but still much cheaper than buying a store bought solar radio and far more cute in this Altoids Tin.

Oddly I now have a complete solar Altoids kit setup in my room. Solar Radio, Solar Flashlight, Solar USB Charger... In the event of a massive power outage (or zombie invasion) I think I'm set.

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wazy8019 months ago
why do you have to drill on step 7?????

To make a hole for an earphone jack

Oh,my radio is the same as yours.

ishiyakazuo3 months ago

Just FYI, the reason that this works and receives a signal through the Altoids tin is because the headphones are the antenna. If you use speakers, you might need a separate FM antenna. Hope this helps.

kfrancis914 months ago

If you break off the solder point from the solar cell, couldn't you just solder it back on?

Skeleton key97 made it!5 months ago

i made it!!!!!! hahaa. its easy enough

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josuchav6 months ago

you misspelt goggles

ajensen276 months ago
found 2 separate lights around the house. one has a 2/3 aa battery and its panel puts out 1.2v and the other has a AA battery and its panel puts out .95-.97 volts sitting under 40w bulb(it was night out). which panel do i use and how many. also do i need the diode?
Kirbsome!3 years ago
Quick tip:
When buying solar powered lights for this, look for blue solar panels.
They are usually higher quality than the dark brown ones.
thanks good to know
JoshuaZimmerman (author)  Kirbsome!3 years ago
Very true. Those CIS are dark brown and very high quality...
This has got to be one of the single most coolest things on instructables!
wazy8019 months ago
what kind of tap do I use o step 8???
Nhoj161 year ago
I just began making this when I realized I'm out of diodes. Will it still function without one?
Nhoj161 year ago
Cool project! I think I have all that I need to make this laying around so I'll definitely do it.
Jacky P1 year ago
What diode do I use?
i suggest a schematic diagram for the project. please to make things simple
Whatat does the diode do in the circuit? Just curious
Orkekum1 year ago
awesome idea and well written, i can buy cheap radio with a scan button and a return one
JoshuaZimmerman (author) 3 years ago
Just because I'm a teacher doesn't mean that I'm not human.

With feelings to be hurt...

Sniff...
teachers are awesome c:
deanes1 year ago
Altoid tins are neat, but maybe an easier more practical project would be to just add the charging panels directly to the radio case? Or, maybe the panels glued to a plastic pocket-shaped sheet and connected by a sturdy wire to the radio battery compartment. Then you would have a solar charging case for the radio.
JoshuaZimmerman (author)  deanes1 year ago
Probably, but this is rather bare bones. Plus cute. You gotta factor in the cute aspect.
DAND3 years ago
What type of diode did you use?
static DAND1 year ago
 The current carrying capability, the voltage rating and the voltage drop across the diode are considerations. Too much current can harm the diode, too much over voltage drop, the batteries may not fully charge. Nominal figures; for the silicon diode used here is .7 V, for the Schottky diode it's .2 V. In most solar application the Schottky is preferred, but one can't walk into radio shack and buy one. In low powered projects like this, it's easier to add an extra salvage solar cell, and used the more readily available silicone diode. No precision is required on the voltage rating here as long as it's higher than the battery voltage, the voltage rating is important if the diode will see a reverse bias as part as normal desired operation.
JoshuaZimmerman (author)  DAND3 years ago
1N914. Very common. You can find them everywhere.
Thanks for the great instructables!
quick question
Are there any differences if you use a 1n914, a 1n4005 or a 1n5819?
JoshuaZimmerman (author)  earm993 years ago
1N914 us just really really common and has a low voltage drop. It's very handy for low voltage low current systems like in this one.

Google the other diodes and check the voltage drop. They probably would work fine for this kind of setup.
Subo692 years ago
if you were to use capacitors instead, which one would you use?
JoshuaZimmerman (author)  Subo692 years ago
Well you'd want some super capacitors. Ones that have 1F or more of power at around 3V.

Actually the best approach would be to get a couple of 1F 5V super caps and hook them up in Parallel. (5V so that you don't overcharge the caps, and can then use a 4V or 4.5V solar cell with the project.)

But you'd need several of them to be on the safe side. Really 3 or 4 if you want to use the radio out of the sun.
This reply is directed more to those that will read the comment made by the author than it is to the author. As science teacher none of the following shouldn't be new to him. F Farad http://en.wikipedia.org/wiki/Farad is not a unit of power.  A capacitor can't be overcharged, but is susceptible to damage from over voltage.  Following the author's suggestions here  the capacitors wouldn't see a voltage over their rating. In my experience, there will be those who would read this and think they could wire lower voltage capacitors in parallel and they would be safe too hook up to a higher voltage source. However wiring the in series  can allow them to be used with a higher voltage source, but the total capacitance will be reduced.  Knowing how capacitors wired in parallel or series behave allows you make use of what you have in the junk box or otherwise can attain readily to come up with what you need.  For more details read http://en.wikipedia.org/wiki/Farad .  Given the low current provided by the suggested salvage solar cells, I'd suggest doing the initial charge of a high capacitance bank from other power source. After that initial charge the solar cells should able to restore the charge in  available time of sunshine.
static1 year ago
Good instructable, but for my kit I have a AM/FM pocket radio that I bought from Radio shack for not much more than the cost here. Use 2 AA batteries, while I hive never tried rechargeable batteries I assume so the solar power should work.  At lower volume levels Alkaline batteries last well, so I'd take extra batteries. My guess is the  plastic radio case doesn't weigh much more than the tin is is more durable. Everyone seems to ignore AM, when AM will be received almost anywhere. Good tools for making holes in light weight metal are a hand metal punch http://http://www.amazon.com/Neiko-Power-Punch-Sheet-Metal/dp/B0002T87CW and a tapered reamer http://www.amazon.com/Empire-Level-27770-T-Handled-Tapered/dp/B001DZE5FW/ref=sr_1_1?s=hi&ie=UTF8&qid=1352666745&sr=1-1&keywords=tapered+reamer .  Links used for illustration purposes so shop around. The punches may cost less  from vendors serving those in the auto DIY crowd looking for bargains.
zinner3422 years ago
Hi Joshua,
I really like your solar powered radio and I am probably going to use it for a school project. But I am confused? How does it all work? My school says that you can use solar power, but is this radio actually using solar power or is it using batteries? When the sun shines on the solar cells, what happens? Does it charge the batteries or what? SORRY, I KNOW I'M ASKING TOO MANY QUESTIONS :P
Thanks,
~ a different joshua ~

:P
the solar cells charge the batterys
aaronXtreme2 years ago
hey I have a biz kind of like what you do and I have been looking for a place to create one your website looks great and I was wondering what site you made yours on?
Hey!This is a great Instructable and I have been planning to make one one these
but i got to know,how many volts do you use on your soldering iron because
they got a 25V,30V,40V,50V and 60V.So what do you suggest I use for this project
and your solar powered Altoids USB charger?
JoshuaZimmerman (author)  Ghosthost54682 years ago
I have no idea. My soldering iron isn't fancy enough to display "volts" used. It just has a temperature wheel with color coating.

Thanks,no sweat,I learnt a little bit about soldering so just do what you do!
Also,I'm on the cheap here cause I'm in Beijing Plus I'm a kid but i managed to fint the exact same radio,so at least I'll be able to complete some of it.
Felixninja2 years ago
Hey Joshua, I saw the exact same radio in a local dollars and sense store, but it says do noy use rechargeable batteries, have you had any problems with the 1st radio?
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