For those who never heard about supercapacitor, you can check for more info about supercapacitor here. Supercapacitor is basically a capacitor with very high capacity, and the capacity rating is normally around few Farads. With the “super” capacity, it basically can store a lot of charge, and I am going to use the “super” capacity to store charges for a 5mm LED. Let’s see how long will the 5mm LED last.
Step 1: Components Needed
The components you will need for this project is basically a supercapacitor (I am using 5.5V 0.1F supercapacitor which I bought from Farnell), a White LED, a 1K Ohm resistor and a USB male connector (I get this from an broken pendrive).
Step 2: Supercapacitor Polarity
Make sure you know the polarity of the supercapacitor, or refer to its datasheet
Step 3: Soldering
The first step is to cut the 2nd and 3rd pin of the USB male connector, we will need only the 1st and 4th pin (5V and 0V pin).
Then solder the negative pin of the supercapacitor to the 4th (0V) pin of the USB male connector.
Now, try to connect the positive pin of the supercapacitor to the 1st pin (5V). For the connection I am using a resistor leg.
Step 4: Soldering
Next, connect the positive pin of the White LED to the 1st pin (5V) of the USB male connector.
Finally, connect a 1K resistor from the negative pin of White LED to the 4th pin (0V) of the USB male connector.
Step 5: Schematic
Please check the diagram below for the complete schematic. You are actually free to use higher Farad supercapacitor, but voltage rating must be larger or equal to 5V, and you can have your creative way to connect all the components together.
Step 6: Testing
Now, plug it to your computer for around 10-30 seconds to charge up the supercapacitor.
You should see the White LED turned on (if it doesn’t turned on, there are some mistake in the connection), then after 10-30 second, you can unplug it and you should have around 10 minutes of the LED light.
Step 7: Circuit Update
Circuit Update (6 Oct 2010)
I made some changes to the circuit, adding another resistor to limit the current consumption from USB port, and an ON/OFF switch to control the white LED.
The circuitry is simple, when you plug it into PC, the USB port will start charging the Supercapacitor, and there is a 10Ohm resistor (R1) limiting the current from USB port to 5V/10Ohm = 500mA maximum, but the R1 will also slow down the charging time. For large capacitance Supercap, you might need to let it charge for around 1 to 2 minutes. At the LED side, the S1 will let you turn ON or OFF the LED, and the 1KOhm resistor (R2) is to limit the current for the LED. If you use smaller value for R2, like 330Ohm, it will increase the brightness of LED but will also reduce the operating time of the LED for one charge. By using larger value for R2, you will increase the operating time, but reducing the brightness. I found 1K to be the balance value for the brightness and operating time.
Talking about the brightness and the operating time balance, I created another circuit that let you choose 3 level of brightness.
Step 8: Circuit Update
In this circuit, the charging and USB port part is still the same, but I add in S2 and R3 at the LED side. So, the S1 and R2 will still function like the previous one, that by switching on S1, you will get the 1KOhm resistor brightness. By adding S2 and R3, it means that if you switch on S2, you will get 330Ohm brightness, which is brighter than 1KOhm brightness, because the resistor that limiting the LED current is now smaller and higher current on the LED means higher brightness. I say you will have 3 level brightness, so, the third level brightness is by switching ON S1 and S2 at the same time.
When S1 and S2 is being switch ON, the R2 and R3 form a parallel pattern, and you need some calculation to get the total resistance for the White LED.
The total resistance from the parallel of R2 and R3:
1/R = 1/R2 + 1/R3
R = 1 / ( 1/R2 +1/R3 )
R = 248.12Ohm
So, the total resistance at the White LED if you turn ON both S1 and S2 is 248.12Ohm which is 3rd level of brightness for the White LED.
- 1st level (S1 ON) – 1KOhm Brightness
- 2nd level (S2 ON) – 330Ohm Brightness
- 3rd level (S1 and S2 ON) – 248.12Ohm Brightness