Step 1: Components Needed
Step 2: Supercapacitor Polarity
Step 3: Soldering
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
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
Step 6: Testing
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
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
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