By using energy harvesting technology I devised a method to power the Internet Of Things board: Mediatek Link it One. By creating a simple circuit using energy harvesting ICs such as the LTC3108 I was able to harvest enough energy from solar sources in low-light conditions to power the Link it One. This board can also be used to power Arduino boards and PICAXE micro-controllers.
In this instructable I shall explain how I did it.
• SSOP to DIP layout breakout board such as these, the side with 0.65mm spacing shall be used http://ebay.eu/1NLeJsQ
• LTC3108 Energy harvesting IC from Linear electronics in the SSOP 16 Lead package (I got these as a free sample off the Linear electronics website but you can also buy them off ebay)
• Coilcraft 1:100 transformer (I also got these as a free sample)
• 330pF capacitor (0805 SMD or through-hole)
• 1nF capacitor (0805 SMD or through-hole)
• 1uF capacitor (0805 SMD or through-hole)
• 220uF Capacitor (either SMD or through-hole)
• 470uF capacitor (either SMD or through-hole)
• Some headers 2.54mm spacing
• A supercapacitor (e.g. 1F, 0.33F)
A N-Channel MOSFET
A 1M resistor
• A type of prototyping board e.g. veroboard
• Some wire for connections on the prototyping board
• A solar cell (should produce 0.55v in bright sunlight.
The LTC3108 coupled with the appropriate circuitry is able to step-up voltages as little as 20mv to 3.3v. I made the suggested circuit as shown on page 1 of the datasheet which I have included for your own convenience.
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Step 1: Solder the LTC3108 to the Break-out Board
This energy harvesting IC unfortunately only comes in very small surface mount but fortunately can be easily soldered to a breakout board into a much more manageable DIP format.
Carefully align the IC on the breakout board (in the correct orientation, the side with the the larger chamfer is the side with pin 1). Heat up 1 corner pad and apply a very small amount of solder. Let it cool. If the IC is not quite lined up, heat up that pad and poke the IC with a pair of tweezers until it is. Do the rest of the legs ensuring that no short circuits are made.
Solder in a header on each side of the break-out board.
Step 2: Solder the Transformer Onto the Proto-board
First you must place the IC breakout board in a sensible place. Don't solder it in place yet as some wires may need to be routed under it.
Then solder the transformer in place.
There are two ways of doing this, either try soldering the transformer directly onto the proto-board or mount the transformer on small stilts. I tried both and found the stilts method to be the best.
Test that the transformer is correctly connected. The 1 coil will have a resistance of 0 ohms. The 100 side coil will have a resistance of about 340 ohms. If not try heating up the connections again.
Then solder in the 330pF and 1nF capacitors next to the transformer.
Step 3: Place on Other Components and Linkwires
Notice how the small SMD caps are connected near the transformer.
The large SMD capacitor is 470uF and is used to smooth Vout and provide high current bursts when needed.
Connect VS2 to ground
Connect VS1 to VAUX.
Connect VS1 and VAUX to ground via the 1uF capacitor
Step 4: Add the 1uF Capacitor.
Step 5: Add the 220uF Input Capacitor
Step 6: Add in Storage Super Capacitor
I soldered in a 0.33F super cap between VStore and GND. At this point I chose to configure the LTC3108 to output 4.1v rather than the 3.3v that I tested the circuit at. 4.1 v can be used to power the LinkIt One board via the Li-ion cell input port.
Step 7: Use PGood to Trigger MOSFET
The PGood output will become high when Vout has reached the correct voltage. I will use this to trigger a MOSFET which will allow current to flow to the LinkIt One board. This reduces the chance that the LinkIt one will waste energy when the output swaps between acceptable voltage limits.
I used a ZVN2106A N-channel MOSFET
An 10 K SMD resistor was used to pull the gate down to ground.
I used a logic level N-channel MOSFET. Source connects to GND. Gate connects to Pgood pin with a 1M pulldown resistor. Link it one GND connects to drain while Link it One Bat+ connects to Vout
Step 8: Testing
I used a solar cell to check that the board worked. First I soldered the Positive and negative output of my energy harvesting circuit onto the battery socket terminals of the LinkIt One (this was because I did not have an appropriately sized plug for the job).
After some testing I found that the energy harvesting circuit was able to power the LinkIt One board for about 10 minutes using the supercap and would then take about 50 minutes to charge in low light levels with the solar cell providing 330mV and 110mA. This energy harvesting circuit may be appropriate for sending data in the form of radio signals from remote locations. The energy harvesting circuit may be more appropriate for less power-hungry microcontrollers such as PICAXE and Arduino.
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