note that you have to subtract the voltage drop over the LED, hence it's R = (Vsupply - Vled)/ Iled, e.g. (5-2)/0.02 = 150 Ohm
/Mikael On 8 Aug 2013, at 00:19, Ed Kelly <morph_2...@yahoo.co.uk> wrote: > Check Ohm's law. > > V=IR, so the resistor you choose is the voltage you provide to the LED > divided by the current it draws. > > e.g. if the LED draws 20mA and you power it from 5V, then the resistor you > need is 5/0.02 = 250 ohms in series with the LED. This current is drawn from > the positive voltage supply through the resistor and then the LED, and then > the transistor. > > This is a fairly good tutorial: > http://www.ehobbycorner.com/pages/tut_transistors.html > > Ninja Jamm - a revolutionary new music remix app from Ninja Tune and Seeper, > for iPhone and iPad > http://www.ninjajamm.com/ > > > Gemnotes-0.2: Live music notation for Pure Data, now with dynamics! > http://sharktracks.co.uk/ > > From: Charles Z Henry <czhe...@gmail.com> > To: Epic Jefferson <jeffreyconcepc...@gmail.com> > Cc: pd-list <pd-list@iem.at> > Sent: Wednesday, 7 August 2013, 20:41 > Subject: Re: [PD] electro-mechanical piano (player piano) - Arduino, > Solenoid Issue > > On Wed, Aug 7, 2013 at 12:05 AM, Epic Jefferson <jeffreyconcepc...@gmail.com> > wrote: > Hey Charles, > > it seems like this might work. i got some pnp transistors and built the > circuit from julianvogels site. > The only problem is that the LED on the test circuit barely lit up. I think > it's because the transistors are not for 20mA, none were available. i'll > check another electronics store to see if i find some. > > I think you just need smaller resistors. Every transistor in a 3-pin package > I've ever seen could run 20mA or much greater. Swapping the transistors will > have no effect on the amount of current. > > Chuck > > > > There are two ways to solve your problem: > > The proper one is to use PNP transistors or P-channel mosfets (remember > I already told you about that ? :)) > > See this document, you can find the wiring at the end: > http://julianvogels.de/wp-content/uploads/2013/06/stromkreis_transistorschaltung_final-1024x627.png > > http://julianvogels.de/extending-pwm-output-pins-with-a-texas-instruments-tlc5940-led-driver/ > > > The good enough one is to put a pull-up resistor (10k works) on every > NPN transistor base, and use the TLC as a pull down. In this case, the > on-time on the TLC corresponds to the off-time on the solenoid. Also > when the arduino reboots and every time the BLANK is issued, every > solenoid will act for a veeeeery short time. This can be a big problem > in your project. I did this for a 96 channels motor+led strip system, > and I regret not using PNPs instead. > > > Enjoy, > > -- > Charles > > > > Epic Jefferson wrote: > > Hey guys, > > > > updating on this project. I got the pwm shields and i've hit a wall. The > > driver circuit I'm using to control the solenoids via arduino is this one > > from instructables > > (link<http://www.instructables.com/id/Controlling-solenoids-with-arduino/)>) > > and > > it uses a single pin to control the pwm signal. > > > > The pwm shield > > (link<http://www.practicalmaker.com/products/arduino-shields/pwm-shield-assembled>) > > is > > based on the tlc5940 which requires each pin to have it's own ground > > instead of a common ground across all drivers. This is a problem because > > all of the information i've found suggest that the signal from the pin > > controls the gate (transistor - TIP102). But i think, in the case of the > > tlc5940, the 5v supply is constant and the ground is being controlled, > > that's why it works perfectly for LED's but seems to be ill suited for this > > circuit. > > > > Any suggestions on how to modify the instructables circuit for use with the > > shields? or would the circuit have to completely change? > > _______________________________________________ > Pd-list@iem.at mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > > > > -- > www.epicjefferson.com > www.avmachinists.org Puerto Rico based Art Collective/ Non-Profit Org > > _______________________________________________ > Pd-list@iem.at mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > > > > _______________________________________________ > Pd-list@iem.at mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > > > _______________________________________________ > Pd-list@iem.at mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list
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