DIY Portable Amplifier

As an avid climber, a full day, or weekend, break from my cellphone and e-mail is one of the best perks. Still, like nearly any activity, good music makes it more enjoyable. This desire to merge two of my passions, climbing and music, resulted in this small, yet robust, portable amplifier.

Here's a video of the final system in action.












Materials

•  LM386 audio amplifier

•  3 Capacitors:

C1 = C3 = 220 microF
C2 = 10 microF

• 4 Resistors: 

R1 = 10 Ohm
R2 = 1 kOhm
R3 = 10 Ohm 
R4 = variable 10 kOhm (w/ an SPST or SPDT switch)

• 9 V battery + battery clip

• Speaker (4 - 8 Ohm)*

*Have a broken sound system? Harvest the speaker! Look for one that can fit in the palm of your hand.

•   1/4" (or 1/8") mono panel-mount audio jack

•  PCB Board

• 22 Gauge stranded wire ( ~ 1 ft)

•  Case**

**There are many options! My case is a mini-lunchbox type thing found at a thrift store for $1. Look around the house, or peruse a thrift store for vintage tins, cigar boxes or metal piggy banks. Look for containers made from metal, wood, or rigid plastics.

• Recommended: Piece of wood for speaker mount

This improves audio output by providing a solid resonant surface. This step was somewhat involved (tool heavy), can be accomplished in many different ways, and is entirely optional, so I will just briefly cover this part of the process.


Tools

• Soldering iron, solder + solder sucker. 
• Epoxy or other bonding agent. 
• Wire strippers 
• Highly recommended: Multimeter. 
• For the case, you also need a drill.
• To mount the speaker in wood: a dremel or other wood cutting tool (+ clamps + eye protection)

Build it! Pt. 1

1. Solder wire leads to the audio input.


2. Solder wire leads to the speaker (recommended to use at least 6" leads).











3. Solder wire leads onto the variable resistor (potentiometer) pins.
Check the resistance between the difference potentiometer pins w/ a multimeter before soldering to determine the functionality of each pin.
Aside: Wire color, while entirely optional, helps distinguish the different pin functions. To wire the potentiometer so that the volume increases from the "off" position: Pin 1 goes to ground, pin 2 goes to LM386 pin 3, and pin 3 goes to the positive audio input.

4. Solder wire leads to the switch pins on the bottom of the potentiometer.
Check resistance across switch pins w/ multimeter. This potentiometer switch has a front pin that goes to ground and the left front pin to positive input.






Build it! Pt. 2

If schematic makes sense, skip next two steps (still suggested to build on breadboard first).

1. Build circuit on a breadboard. Recommended to draw out how it will transfer to the PCB board pads.

Connect a battery and check audio input w/ either a multimeter or an actual source (will need a 1/4" or 1/8" headphone cable).

2. Solder LM386 amplifier to PCB board.











3. Solder the battery clip leads and potentiometer switch leads to the PCB board.
The potentiometer leads are inserted between the positive battery lead and the 10 ohm resistor going to the LM386 voltage source pin.
Note: If your variable resistor does not have a switch, it is highly recommended to include a power switch for the battery.


Build it! Pt. 3

1. Solder the remaining components to the PCB board using the PCB pads and/or wires (breadboard pictured for clarity).

A. Connect LM386 pins 2 and 4 to ground.

B. Connect 1kOhm resistor and 10 microF capacitor from LM386 pin 1 to pin 8 (shorter leg (negative pin) of the capacitor connects to LM386 pin 8).











 C. Connect the long leg (positive pin) of the 220 microF capacitor to LM386 pin 5. Connect one side of the 10 ohm resistor to the short leg of the capacitor, and the other side of the resistor to ground. Connect the positive speaker lead to the short leg of the capacitor, and the negative lead to ground.




D. Connect one side of 10 ohm resistor to LM386 pin 6 and other side to positive battery (w/ switch). Connect long leg of 220 microF capacitor to LM386 pin 6 and short leg to ground.












E. Connect the potentiometer pin 1 to ground, pin 2 to LM386 pin 3, and pin 3 to positive audio input.

F. Connect negative audio input to ground.

Case it! Pt. 1

1. Plan + mark location of each of the components.
The potentiometer, or volume knob, power switch, audio input, and speaker are installed on the exterior. The PCB board and battery are on the interior.










2. Drill two holes in case exterior for the potentiometer knob and for the audio input.
If case is not metal, recommended to include a sheet of metal to provide a better ground for the audio input.

3. Remove screw heads from potentiometer knob and audio input. Push potentiometer knob and audio input through the holes and reattach screw heads.

4. Check connections w/ a multimeter and/or an actual audio input (will need a 1/4" or 1/8" audio cable).







5. Dab epoxy onto bottom of case to adhere the PCB board.
To secure the 9V battery: use velcro strips, or make a quick fabric pouch and epoxy the pouch to the case.

Case it! Pt. 2
1. Mount the speaker in wood or in case exterior.
There are different options depending on your chosen case and available tools. It sounds great w/ wood, otherwise you can also mount it directly to the exterior of the case.

One option is to follow the design featured in this tutorial:

A. Cut a piece of wood to fit inside the case (bottom slab). Cut a hole in the middle large enough to pull the speaker through.
 



B. Take a thin piece of wood and cut a notch out. The notch should be sized so that the screw holes of the speaker frame sit on top of the wood.










 C. Optional: Screw speaker into top wood ring. Screw top ring into bottom slab.

Test & Go Adventuring!

Test the electrical connections by plugging in an audio source (e.g. electric guitar or mp3 player). Check that the potentiometer effectively controls the volume and that the switch turns the system on/off. Once everything is working, coat electrical connections in epoxy.

Take your new portable amplifier to bring music to your next outdoor adventure!

LED Proximity Sensor Gloves

 
This is a minimalistic design for a proximity sensor glove: a light-up glove that dims in brightness when an object, or person, is close to the sensor. This project costs less than $10, although it does take some time to build (1 - 2 hrs).

This is also a modular design, meaning that it is easily customizable and can be used in other projects.

Here's a video showing the glove in action.

Materials

-- Gloves (fingertips optional)
Pretty much any type of glove will work. I chose simple cotton ones (that are well worn and have character) because it's easy to sew components into these gloves and, if necessary, can easily (& cheaply) be replaced.
-- LEDs!
I had 5mm white LEDs on-hand, so I used 10 for one glove. As long as each LED has appropriate resistance, you can (pretty much) add as many as you want.
I strongly recommend getting surface mount LEDs or wearable LEDs. They are a bit more expensive, but are much more aesthetic for this type of project and are waay easier to sew.
-- Conductive thread
This is one way to connect + attach the LEDs. I chose conductive thread b/c it looks cool and incorporates the circuit into the glove material, acting as both a conductor and an adhesive. Other options include wire or alligator clips.
Disclaimer: When using conductive thread, be super careful of short circuits. I set my conductive thread on fire more than once during this build process..
-- Photoresistor
-- Five 1 KOhm resistors (one for each pair of LEDs)
The value and number of your resistors may change depending on your battery + LED type.
-- 9V battery + battery clip
-- Switch (optional)



Tools 

-- Scissors
-- Sewing needle
-- Hot glue gun, epoxy, or other quick-drying adhesive.
-- Soldering iron (optional)
You can build the glove without a soldering iron by tying conductive thread tightly to a component, then coating in hot glue or other adhesive.
-- Multimeter (highly recommended)
A multimeter is super useful for checking electrical connections.


Build it! Pt. 1

If a breadboard is available, use it to test the circuit.

1. If you have a switch, connect one end to a battery clip lead.
Solder the two wires together, or use conductive thread + hot glue.

2. Determine layout of the photoresistor(s), LEDs, and resistors.
You can follow my schematic or you can add more LEDs and/or photoresistors (recommended b/c it's cooler). Here's a helpful website to calculate the circuit resistance. Remember that the photocell also adds some resistance (mine was between 300 Ohms and 1 MOhm).
In my layout, two LEDs are connected in series with a resistor, as in the breadboard photo above. These in-series LED pairs are then connected in parallel with all other in-series LED pairs.
Aside: Diode forward voltage & current depends on the color. These white LEDs were ~ 3.4 VDC and 20 mA. Use Google or this page to find forward voltage and current for your specific LEDs.

 




3. Turn glove inside out and mark location of the LEDs, resistors and photoresistor(s).

4. Sketch the positive and negative connections onto the glove w/ a pen. Label the + and - lines.
This step is especially helpful b/c 3D circuits can be a bit confusing.








Build it! Pt. 2

1. Attach the photoresistor to the glove (and add a positive battery lead to the glove).
Make a slit in the glove or push the photoresistor wire legs through the fabric (be sure the legs are on the inside of the glove). To hold it in place, dab hot glue or sew legs to glove with regular thread.

Tie conductive thread to one end of the photoresistor (either leg works), and sew thread through the glove to the bottom. Leave a few inches of thread at the end for the the battery connection. Coat connection in hot glue.





2. Attach a resistor to the positive leg of one LED. Repeat for one LED in each set of LEDs that are in-series (5x for this configuration).

Wrap the two ends together and, if possible, solder the connection. Remove excess wire and coat in hot-glue to adhere connection and cover sharp ends.








Build it! Pt. 3 

1. Attach the LED + resistor to the glove.
Poke the ends of the LED through the glove (or make a slit). Tie conductive thread to LED legs and coat in hot glue to hold components in place, and to cover sharp ends.
Be careful to avoid shorting the LED legs with the conductive thread.

2. Connect the LED + resistor to the open leg of the photoresistor.
Sew conductive thread from the resistor leg to the photoresistor leg, then tightly tie thread to photoresistor leg. Coat connections in hot glue.









3. Connect the next in-series LED.
Connect the positive leg of the next in series LED to negative leg of the previous LED.
Depending on the type and number of LEDs you are using, you may have one, two or more LEDs in series w/ the first LED + resistor.

4. Repeat Steps 1 - 3 for all LEDs in parallel.


























Build it! Pt. 4

1. Once all the LEDs + resistors have been installed, add in a negative battery lead.
Consider where you want to put the battery before adding in leads. You can attach the battery directly to the glove, hide it inside the glove, or install long leads to allow the battery to be placed elsewhere on your body.
My initial design used conductive thread for both battery leads, but this shorted the glove so many times I replaced them with an alligator clip in the final design. This works much better, is safer, and is seriously recommended over conductive thread. If you don't have an alligator clip, any insulated wire will work.




2. Label the positive and negative battery leads.

3. Optional: Solder the battery clip leads to the glove battery leads and dab with hot glue.
Alternative options include alligator clips or twisting wires together + coating with hot glue.

Test & Wear!

Be sure to test your design BEFORE you wear it because if there are shorts in the conductive thread it will probably catch fire. So, please be careful and be sure that the positive and negative sides of the circuit do not touch.
The connections can be a bit finicky. Be patient and check the electrical connections w/ the battery or a multimeter (if you use a battery, be careful to avoid shorting the circuit). Fix and add more hot glue as necessary.
Once you know it works, put on the glove(s) and impress your friends!
Happy hacking!

Faraday Cage Phone Pouch

 
This Faraday Cage phone pouch blocks all radio signals coming in or out of your cellphone. Material costs are about $10, it takes ~ 30 minutes to build, and it can fit in your pocket!

The purpose of this pouch is to prevent access to your phone and its data (e.g. location) if and when you so choose. Before placing in the pouch, be sure to put your phone in airplane mode as the phone will drain its battery trying to find a signal.

Materials

-- Conductive Fabric
Sized to fit your phone + a top flap. For an iPhone w/ a (giant) case, I needed about 7.5" x 3.5".
-- Thread (regular, any color)
-- Button (any type)
Alternatively, you can use velcro, a safety pin, or any other means to hold down the top flap.


Tools  

-- Scissors
-- Ruler
-- Needle or Sewing Machine (preferred)
-- Safety pins (optional but helpful)


Build it! Pt. 1 

1. Measure the width, height, and depth of your phone (+ case, if you have one).

2. Add 1" to your phone width measurement and 2" to your phone height measurement. Cut conductive fabric into a rectangle of that size.
For example, the iPhone 5 is 4.87" tall, 2.31" wide and 0.30" thick. Thus, you want a rectangle that is at least 6.5" tall and 3.5" wide.

To double check your measurements, mark where you plan to cut the conductive fabric w/ a pen or pencil. then wrap the fabric around your phone. Be sure that you can fold down the top of the conductive fabric.
Helpful tip: It's always better to leave extra room. Measure twice, cut once, and so forth.

3. Place phone on one side of the conductive fabric and fold the fabric over the phone. Safety pin sides together.
Leave an inch or two above the phone so the top can be folded over like an envelope.















Build it! Pt. 2 

1. Sew bottom + sides of conductive fabric together using small hand stitches or a sewing machine.

 

2. Turn pouch inside-out to hide stitching.
3. Place phone inside pouch, fold top down and mark where the button will go.








4. Sew button on & cut a small slit in the top flap to attach.

Remove excess fabric as necessary, but be sure that the conductive fabric completely encases the phone when the top flap is folded down.













 
Done!

Place phone inside the Faraday Cage pouch whenever you want to cut off all radio signals coming in and out of your phone.

For another awesome version of the same concept, check out my friend's scarf project here.

Curious as to how this works? Awesome! In super simple terms, a Faraday Cage "traps" radio waves in the wires that make up the cage. In this design, the conductive fabric threads are the metal wires that form the Faraday Cage. Due to the small mesh size (aka wires are super close together), this design will block any electromagnetic radiation with a wavelength larger than visible light. :)

Here's a good overview on what a Faraday Cage is and how you can build a different version.

And here's the Wikipedia blurb on Faraday Cages, an excellent source if you want to learn more!

Versatile Wearable LEDs

Wearables (aka Wearable Technology) are a new & insanely awesome extension of electronics. These minimalistic, versatile, and detachable lights are designed to allow for a wide variety of creative possibilities and to be accessible to makers of all ages and backgrounds.

The process takes about an hour and materials costs are less than $10 per LED strip (not including the battery). Even the pooch can have a light-up sweater!

Materials

- LED strip(s)
Here's a link to purchase the specific LED strips used in this project: 12 white surface LEDs with a forward voltage of 7.4 - 15 V and forward current of 50 mA.
If using different LEDs, note the forward voltage & forward current and use this calculator to determine the necessary resistance.
-- Male and Female JST connectors
The Tarot LED strips came assembled w/ male JST connectors, so those were the easiest & most practical. They work rather nicely for this project, and I recommend using them if you are new to electronics.
-- 33 Ohm Resistor
-- Switch
So many options for switches! For this project, I suggest an SPST (single-pole-single-throw) maintaining switch (aka toggle or on/off switch). I had a DPDT slide switch on-hand so that's what I used for this tutorial.
-- 9V battery (preferably rechargeable)
Any battery w/ a voltage output from 7.4 -15 V works. LiPo batteries are the best (and last the longest), but are more expensive.
-- Velcro (sticky side only)
-- Optional: Custom Battery Case
Version 1: Two safety pins & a 3" x 2" piece of fabric.
Version 2: Strong rare earth magnet (or two).
This is a more expensive but simpler alternative to the fabric battery case.

Tools

  

-- Soldering iron
-- Hot Glue Gun
-- Wire Strippers
-- Needle + Thread
-- Scissors
-- Recommended: Epoxy
My favorite method to make extremely permanent (+ weather resistant) electrical connections.
-- Also recommended: Multimeter & Breadboard (for testing)


Build it! Pt. 1

 















Prep: If LEDs lack wires, solder the male JST connector leads to the uppermost LED pads. Coat in a dab of epoxy or hot glue.
Recommended to test the circuit on a breadboard before soldering.
1. Attach sticky-side velcro pieces to LED strips.

2.Solder the female JST connector leads to the switch.


If using a DPDT switch, as in the schematic, each set of legs can control a separate circuit. Instead of connecting ground to the switch, you can also connect the LED ground to the battery ground. This allows you to control another set of LEDs (+ resistor) on the same switch + battery.
If you're just starting out, here's a helpful guide on switches.

Build it! Pt. 2

1. Solder the resistor to the middle switch pin on the same side as the positive JST wire.
2. Solder the positive lead of the battery clip to the resistor & the negative lead to the negative middle switch pin (or connect them together).
Clip off excess wires.









3. Connect LED strips via the JST connectors and check that the switch works.
4. Coat bottom of switch in epoxy and/or hot glue.
Be sure to avoid getting glue on the moving part of the switch esp. if using epoxy. Check that it can move while epoxy is drying.



Build it! Pt 3 (9V Battery Case)

1. Sew your chosen fabric square into a pocket for the 9V.
2. Place 9V battery in case and attach the battery clip.












3. Sew battery clip + switch to back of fabric case (face switch outward).
4. Attach safety pins to back of fabric case.

 







For magnet battery holder alternative:
Some rechargeable batteries, such as NiMH (Nickle Metal Hydride), are magnetic. For these, place battery inside clothing, then place magnet on the outside to hold the battery in place.
If the battery is non-magnetic (e.g. lithium), hot glue one magnet to the battery, place inside clothing, then place another magnet on the outside of your clothing. Be sure to keep the magnet when switching out the battery!

 Test & Wear!

Double check that the switch successfully turns on and off the LEDs. Attach the battery+switch to clothing by safety pinning (or magnetically attaching) the battery to a comfortable place. The velcro adheres best to soft fabrics, like sweaters, tights, fleece, etc.

Be creative and experiment with the basic module on assorted clothing and accessories for yourself, your friends and your pet(s)!