It depends on the colour and the LED technology. The energy of red light
is about 1.5eV and blue is 3eV. Add to that internal resistance of the
device. An ordinary diode (not a LED) emits infrared around .6eV, which
is the voltage drop of a silicon junction.
Martin
On 2013-08-07 20:02, Ed Kelly wrote:
Oh, thanks.
That was dumb I didn't remember that!
Is it really 2 volts drop for an LED? I should know this stuff...
Ed
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:* Mikael Fernström <mikael.fernst...@ul.ie>
*To:* Ed Kelly <morph_2...@yahoo.co.uk>
*Cc:* Charles Z Henry <czhe...@gmail.com>; Epic Jefferson
<jeffreyconcepc...@gmail.com>; pd-list <pd-list@iem.at>
*Sent:* Thursday, 8 August 2013, 0:26
*Subject:* Re: [PD] electro-mechanical piano (player piano) -
Arduino, Solenoid Issue
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
<mailto: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
<mailto:czhe...@gmail.com>>
*To:* Epic Jefferson <jeffreyconcepc...@gmail.com
<mailto:jeffreyconcepc...@gmail.com>>
*Cc:* pd-list <pd-list@iem.at <mailto: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
<mailto: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?
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