Instructables

Step 8: Circuit Update

Picture of Circuit Update
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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

Source: http://www.bustatech.com/supercapacitor-usb-light/
 
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it would be great to put a couple of supercap in paralel to get a larger capaticance, and you forgot that if not healty for supercaps to charge them with unlimited current, the USB port has a limmited current to 500mA , and it would be great to add some PWM to circuit, it's more efficiant than a ressistor, besause the ressistor turns the unused energy to heat, so the NE555 SMD in C-mos used like PWM would be perfect for this project

PS, there are supercap that has a capaticanse of 7F but only 2V , add a hand generator to charge it and a 1,5V LED driver and ingoy your hand rechargeable flash light.

sorry for bad english, I'm from Serbia :)
I know of a company that makes 150F supercapacitors at 1.5-2vdc for use in industrial applications
I never heard that much of capacitance before. 150F supercapacitors, that's monster size... I wonder what kind of circuit will need that amount of capacitance.
resently maxwell tecnologies came out with a 3000F 2.7V Boost cap! :D it's now avalible on the consumer market the only place i know that sells these is electronics goldmine and mouser there very nice capacitors and thier about 20-30$ on avrage each but if you get lucky you can get them for 10$!!! oh an answer to your qestion, these high capacitence capacitors are used in green energy, energy storage, and well as hybird cars :D
thank you for your answer :)
nclark5573 years ago
when i make this im going to put in a small switch from radio shack and make a case for it great job man
vosgians3 years ago
i french and i speak litle english i said just for you on trick to simplify your "calculations" i dont think this is the good word xD.

when you have 2 resistor "parallele" you can write and only if you have two resistor "parallele".

(R1+r2)/(r1+r2)

i like your instructable thank you.

@dragon_shadow88 good idéa for the 555 but it's hard to make it, if you want make it in a minimal space.

sorry for my english i'm french xD
Just a note I think the equation is slightly wrong there. It should read:

(R1xR2)/(R1+R2)

As 2 parallel resistors can be given as product-over-sum. :)
coleyy4 years ago
why cant you just put in a variable resistor