For this project we are going to take advantage of supercapacitors to power a vibrobot. In other words, we are going to be using 15F capacitors to power vibrating motors to make robots which move around through vibrations. The basic model has an on/off switch and a charging port to allow it to be charged up between uses. The more advanced version also includes a small solar cell to let it be charged by the sun when not being used.
To learn more about capacitors, check out the Electronics Class. And should you have robots on the brain I have a Robots Class too!
Step 1: Materials
For this lesson's project you will need:
(x1) 15F supercapacitor
(x1) 100 ohm resistor
(x1) Vibrating motor
(x1) Circuit board
(x1) SPDT through-hole switch
(x1) JST-XHP 2-pin male and female connector set
(x1) 2-wire power adapter
(x1) Adjustable voltage supply
(x1) 4V Solar Panel
(x1) 1N4001 diode
Step 2: The Circuit
The vibrobot circuit is fairly straight-forward.
There is the charging power that has a power and ground connection.
Ground gets connected to the capacitor and the motor.
The power input goes to a SPDT switch through a 100 ohm current limiting resistor.
The SPFT switch toggles the capacitor's positive connection between the charger and the motor. In this way, it allows the capacitor to either be charged by the input port or power the motor.
Step 3: Attach the Capacitor
Let's start the circuit board by soldering the supercapacitor in place. Notice that the capacitor has a metal plate on the bottom connected to the power pin. You need to be particularly careful not to accidentally short the power by having the bottom of the capacitor touch any bus rows on the circuit board that might be connected to ground. To easily prevent this, I installed my capacitor at a 45 degree angle straddling the center of the board. This arrangement ensures that a short between power and ground like this likely won't happen.
Step 4: Install the Socket
The next thing to install is the female socket for the power plug. Place this on the same side of the board as the capacitor's ground lead. Place it somewhere in the middle with the indent for the plug's tab facing outwards away from the board.
Note that I have something jammed under the board in the soldering picture. This is to hold the component in place while I solder it.
Step 5: Switch
Install the on/off switch on the side of the board opposite from the charger socket.
Step 6: Wires
Strip about an inch of insulation off the end of solid core wire. Attach the uninsulated wire to one of the terminals on the vibrating motor. Repeat this process for the other terminal.
Step 7: Wire in the Motor
Place the motor centered upon the edge of the board such that its counterweight hangs over the edge.
Insert each motor wire through one of the sockets on their respective sides of the circuit board, and solder them in place.
Step 8: More Wiring
Attach black ground wires between the 2-pin female socket, the ground pin on the capacitor and one of the motor pins.
It is critical to get the connection between the ground pin on the socket and the supercapacitor correct. If you were to reverse it and charge the capacitor backwards, very bad things can happen. So... double check this and make sure you are getting it correct. When the plug is inserted, the ground pin should be wired to the pin with the negative marking on the capacitor.
Once you are absolutely sure you got the ground connections right, solder a red wire between the center pin on the switch and the positive pin on the capacitor. Also solder a red wire between one of the outer pins on the switch and the motor.
Finally, solder a wire around the body of the motor. This shouldn't be electrically connected to anything. It just holds the motor in place.
Step 9: Charging Resistor
Solder a 100 ohm resistor between the voltage pin on the power socket and the unused pin on the switch.
This resistor is used for charging. If we didn't use the resistor, the supercapacitor will try to draw as much current as it possibly can from the charger. This sudden surge will essentially be like a short wire and possibly either damage it, or if it has protection circuitry, do nothing at all.
The resistor we are using was calculated using Ohm's Law. To be on the safe side, I upped the value slightly since resistors are not perfect, and it can't hurt to have a little bit more.
All of that said, the particular supercapacitor that is being used here has a relatively high internal resistance. What this means is that it does not draw power from a charge as fast as a normal supercapacitor. In fact, it takes an exceptionally long time to charge (about an hour as opposed to 10 seconds).
The resistor we are using may not be necessary and might actually slow down charging times a bit. Nevertheless, I have included the resistor in case someone decides to use a different supercapacitor.
You may be wondering why I have chosen to use this one if it charges so slowly. Well, it holds 15F of power, and is a fraction the size of normal supercapacitors. Basically, this little cap holds 3X more power than a supercapacitor that is 5X the size. It may take a while to charge, but it can run for a relatively long time.
Step 10: Cut Wires
Cut four 4" solid core wires to be used as the robot's legs.
Step 11: Attach the Legs
Solder both ends of each wire into the corners of the circuit board to create four wire loops.
These should not be electrically connected to any actual components on the circuit board.
Step 12: Shape the Legs
Shape all four wires into legs as you see fit.
I gave each one little loop feet, but perhaps there is another design which might work better. Feel free to experiment with form and aesthetics. There is no true right answer.
Step 13: Determine the Polarity
We are going to use a 'wall wart' AC to DC converter to charge the vibrobot.
In order to do this, we need to first determine the polarity of the plug connected to the wall wart to determine which end is positive and which is ground.
Plug the 2-wire adapter into the socket at the end of the cable. Use the voltage setting on your multimeter to measure the voltage coming off of the adapter. If you see a positive voltage, then the wire connected to the red probe is positive and the wire connected to the black probe is ground. Mark these wires to tell them apart if they are not marked already.
Step 14: Connector
Solder the metal sockets for the 2-pin female connector onto the end of each wire of the 2-wire power adapter.
Make note of the alignment tab on the plug. If the alignment tab is facing you and the connector is pointing up, ground should be on the left and power should be on the right.
Compress the the metal tabs on the end of each pin and then insert both into the proper socket of the plug by pressing them firmly.
If you are not confident, you can plug the power adapter in and measure with the multimeter to make sure you got it right.
Step 15: Charge It Up
To charge it up, make sure the switch is in the charging position (i.e. the motor is not running), and plug the wall wart into the socket.
You can leave it plugged into the charger as long as you want. The capacitor will stop drawing power once it's charged and be fine. Capacitors are not like batteries whose shelf-life is diminished if you leave them charging for too long without protection circuitry.
Step 16: Solar
If you want to take your robot off the grid, you can add a small solar panel to charge up the capacitor when the motor is not in use.
This addition is optional.
Step 17: Expanding the Circuit
To make this circuit solar powered, we need to add two additional components, a solar panel and a diode.
The solar panel should be rated for less voltage than the capacitor, and placed in parallel with the capacitor. Since our capacitor is rated for 5.6V, using a 4V solar panel should be safe for charging it.
We will also need to add a diode to the circuit between the positive lead on the solar panel and the capacitor. Don't yet worry too much about what diodes are. They will be discussed much further in a future lesson. For now, you just need to know that all the diode is doing is preventing electricity from the capacitor flowing backwards through the solar panel when there is no sunlight hitting it.
Step 18: Adding a Diode
Simply connect the end of the diode with the stripe to the pin on the switch where the 100 ohm resistor is connected. Connect the other diode pin to any unused solder pad on the board.
Step 19: Wiring the Solar Panel
Attach a red solid core wire to the positive terminal on the solar panel and a black wire to the negative.
The reason we are replacing the existing wire with solid core wires is because these new stiffer wires will hold the solar panel in place upright above the surface of the board.
Step 20: Connect the Solar Panel
Connect together the red wire from the solar panel to the unused pin on the diode.
Connect the black wire from the solar panel to any of the other ground connections on the board.
Your robot is now powered by renewable energy.
Now is time to turn your robot on and let it loose.