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[00:05:17] <cehteh> Eszett_: just a wild guess: it detects if usb is plugged in, when you want to power the chip from usb you need some external stuff to connect to normal vcc
[00:06:28] <cehteh> ah and looking at the datasheet, it internally generates a 3v3 reference from uvcc
[00:07:00] <Tom_L> yup
[00:08:09] <cehteh> Figure 21-3.
[00:08:10] <cehteh> Typical Bus Powered Application with 5V I/O
[00:08:23] <cehteh> just read the datasheet more carefully ..
[00:09:04] <cehteh> there are plenty examples down there
[00:11:00] <Eszett_> thanks, i will read that section..
[00:11:23] <cehteh> just read the whole datasheet :D
[00:11:31] <Tom_L> there are 3 basic configurations for that
[00:11:43] <cehteh> i mean its your project...
[00:11:54] <Tom_L> 5v io, 3.3 using the chip reference or 3.3 using external source
[00:12:07] <cehteh> i find important information for you while watching anime just looking at the datasheet .. grr
[00:20:36] <Eszett_> Actually I can't "read" that datasheet because there are no sentences that explain anything. It just a load of tables, numbers, illustrations, sorry its all gibberish for me.
[00:23:08] <cehteh> hum
[00:23:15] <cehteh> well .. work . .taxes grr
[10:05:16] <_ami_> sabor: did you order anything from banggood? how much time does it take to reach?
[11:43:15] <ScrumpyJack> .
[17:16:05] <Eszett> I have a question: When i want to calculate RL (resistance of the load) of a LED together with its current limiting resistor: may I ignore the current limiting resistor in that calculation or do I have to include it?
[17:21:10] <Lambda_Aurigae> well, if the resistor is part of the load, no, you can't ignore it.
[17:21:32] <Richard_Cavell> `in my experience the resistance of the resistor is way higher than the LED.
[17:21:35] <Richard_Cavell> Am I wrong about that?
[17:21:50] <Lambda_Aurigae> depends on the resistor.
[17:23:15] <Eszett> Richard: ye in my case yes
[17:24:30] <Lambda_Aurigae> again, if the resistor and LED are both part of the load, then, they both need to be in the calculation.
[17:25:14] <Eszett> Lets say I want to drive 2 LEDs which have a forward voltage of 3.3V and Id' like to deliver them 5mA each from my 5v USB source. Then I have to put a cuurrent limiting resistor of 340 Ohm in front of them. That is easy. But now id like to have a NPN transistor there, that switches the LEDs on and off. I have to calculate the base resistor value for this transistor, and now it gets tricky..
[17:25:46] <Lambda_Aurigae> I just guestimate it.
[17:25:51] <Lambda_Aurigae> but, I'm not trying to do homework either.
[17:26:04] <LeoNerd> Don't forget
[17:26:10] <LeoNerd> Don't forget Vce of the transistor
[17:27:36] <Eszett> For the calculation of the base resistor value I have to calculate RL first, and that is 5V / 0.01A = 500 R (?). Im not sure here since I have not included the current limiting resistor value of the LED in that equation
[17:28:27] <Eszett> So my question is if RL is 500 Ohm, or did I do a mistake?
[17:37:23] <Eszett> LeoNerd: the voltage drop over C+E should be 0V, as the transistor acts as a fully saturated on/off switch, no?
[17:40:03] <Lambda_Aurigae> in an ideal world.
[17:45:26] <LeoNerd> Not really
[17:45:44] <LeoNerd> Vce for a typical silicon transistor is about 0.7V
[17:46:22] <LeoNerd> Which, given a 5V supply an a Vf of 3.3V on an LED, is suddenly quite a significant drop
[17:51:08] <Eszett> But one formula that is given for calculating the Rb is: Rb = 0.2 × hFE × Vc / Ic and i know dont know how to put any voltage drop of the transistor in there (or any voltage drop of the LED-current-limiting-resistors)
[18:50:43] <antto> Eszett if it helps.. you could try throwing that into a circuit simulator and see if you're right
[18:50:51] <antto> i propose falstad.com/circuit
[19:00:54] <Eszett> antto: nice, how can i add a transistor on falstad?
[19:13:51] <Eszett> ok, got it so far, i could setup this basic schema:
http://tinyurl.com/z4oprj6 but how do i edit the parameters for the transistor like voltage drop?
[19:27:58] <Eszett> yes that was a good idea from you antto, playing with falstad answers many questions
[19:32:16] <Eszett> but damnit i cant create any link if the circuit is more complex. the url shortener gives an error the url is too long o_O