[PD] electro-mechanical piano (player piano) - Arduino, Solenoid Issue

Mikael Fernström mikael.fernstrom at ul.ie
Thu Aug 8 01:26:55 CEST 2013


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_2016 at 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 <czhenry at gmail.com>
> To: Epic Jefferson <jeffreyconcepcion at gmail.com> 
> Cc: pd-list <pd-list at 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 <jeffreyconcepcion at 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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> 
> -- 
> www.epicjefferson.com
> www.avmachinists.org Puerto Rico based Art Collective/ Non-Profit Org
> 
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