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16  Using Arduino / General Electronics / Re: powering two SMA wires on one power source on: December 14, 2013, 12:11:27 pm
Oh, that diagram is just wrong! If you are wired like that, you have to fix that before proceeding.

http://www.fairchildsemi.com/ds/TI/TIP122.pdf

Problem is TIP120 is not a straight NPN transistor - it is 2 NPN connected in Darlington fashion, where 1st NPN provides extra drive to the 2nd for higher Collector-Emitter current flow. The drawback is higher Collector-Emitter voltage drop, closer to 2V than say 0.5 or 0.7V.

That may work out okay here tho:
(5V - 2V)/(7.8 ohm) = 384mA.

If the 5V is something else, re-do the math and add the appropriate current limit resistor.


ah, you know what, I am new to schematics so I didn't realize how wrong that looked. I used a generic transistor on my build tool, I guess the pins were flipped (schematic gets build almost automatically from breadboard tool). I do in fact have the digital pins from arduino going to the base, not the collector. For the most part I have exactly what you have in my actual breadboard.

yeah I have 12v on it so the resistor was 14.4ohms.
17  Using Arduino / General Electronics / Re: powering two SMA wires on one power source on: December 13, 2013, 03:48:11 pm
I can't open that link.

Are you connecting the wires in series or in parallel?
The transistor will also have a voltage drop across it, probably approaching 2V with 400 or 800mA.  You need to adust your resistor to account for that:
(12V - 2V)/.4A = 25 ohm - 15.6 ohm = 10 ohm resistor.
Presistor = I^2*R =  0.4 * 0.4 * 10 = 1.6W, so at least a 2W rated resistor.


ah, interesting. how do I know what the voltage drop is? I tried to look up info on transistors but they mostly consist in explaining how the E C B works... if you have any suggested reading I would definitely put the work in.

they are in parallel I believe. here is another upload, not sure why other link isn't working http://i.imgur.com/HjzM0qK.png
18  Using Arduino / Sensors / Re: Capacitive Touch Piano on: December 13, 2013, 03:37:42 pm
on this same code i have the 'CapacitiveSensor' does not name type error pleas help smiley-sad


on this line

// Defines the pins that the keys are connected to:
CapacitiveSensor keys[] = {CS(3), CS(4), CS(5), CS(6), CS(7), CS(smiley-cool, CS(9), CS(10)};

and if i put #define CapacitiveSensor keys[] = {CS(3), CS(4), CS(5), CS(6), CS(7), CS(smiley-cool, CS(9), CS(10)};
it gets me to the problem of  keys was not declare in this scope  on the first void setup


make sure you download the library and install it, as well as add the header file at the top of your code:

Code:
#include <CapacitiveSensor.h>
19  Using Arduino / General Electronics / Re: powering two SMA wires on one power source on: December 13, 2013, 03:30:02 pm
Quote
9v 30mA
I thought you were 0.006 wire that needed 400mA?

this is where I get a bit confused on amps. going to rubber ducky it... so amp rating on a transformer is how much you can pull and volts is actually volts of what comes out of the transformer.

I need 400mA or .4A so....

I have two 6in wires, thats 7.8ohms *2 = 15.6ohms resistance in the wires. and I have another transformer that is 12v 1A:

(12v/.4A)-15.6ohms = 14.4 ohms

ok so I need to add a resistor to this circuit... so it would be more accurate to do this:
https://www.dropbox.com/s/aap9xehi068knlp/Screenshot%202013-12-13%2015.34.10.png

so by using those resistor values I am limiting current to .4A? I am not sure if that works with how I have it wired. Also since its going through the transistor would I still need a high watt resistor like a 5w? when I connected directly to transformer, it seems to be an issue, but when I had it on the tip120 it wasn't an issue, so not sure if it was limiting current somehow?

edit: also looking and schematic it seems I could simplify the pin out with just one R1 resistor as well...
20  Using Arduino / General Electronics / powering two SMA wires on one power source on: December 13, 2013, 12:09:36 pm
I'm using a tip120 transistor to control some flexinol SMA wires. I can easily get one to work, but seem to be having issues when I try to drive both the wires with one power source, I'm assuming it has to do with fact that the current is being split between the two wires? and if so, not sure how to increase the current between the two-- would I just increase the voltage? with SMA it seems that current is the most important part.

if I increase the current I am not sure if that is ok with the tip120-- just started using these.

here is a schematic of how I am wiring it: https://www.dropbox.com/s/2fp01vgoz050r7h/Screenshot%202013-12-13%2012.01.28.png

the battery is actually a 9v 30mA transformer though, R1 is 2.2k and other resistors are the SMA wires.

here is also a link to the breadboard that can be forked http://123d.circuits.io/circuits/70276/
21  Using Arduino / General Electronics / Re: figuring out resistors for SMA on: December 12, 2013, 04:10:44 pm
.4*.4*22 is 3.5 W, so you need a pretty big resistor to handle the power.

ah, I was assuming it might be a watt thing. thank you.
22  Using Arduino / General Electronics / figuring out resistors for SMA on: December 12, 2013, 03:57:56 pm
so i keep burning out resistors for some reason, anyone know why? I'm using this data sheet http://www.robotshop.com/media/files/pdf/flexinol-technical-data.pdf

at 6in it should be 7.8ohms resistance on the .006diameter wire
which leads to equation:

 (12v/.4a)-7.8ohms = R
which i get to be 22ohm resistor.

but when I connect it the resistor burns up pretty fast.
23  Using Arduino / Installation & Troubleshooting / Serial port already in use. on: December 12, 2013, 10:41:42 am
I am using a leonardo and for some reason I can only upload sometimes to it. I've noticed it happens usually only when I have serial communication happening, I am assuming its because leonardo continues to read serial even when window is closed.

I am on OSX and have tried two things:
1. adding delay in setup of 5seconds so I could try a reboot and upload right after its been rebooted.
2. this suggestion http://www.baldengineer.com/blog/2012/10/08/arduino-fixing-serial-port-in-use/

not sure what else it could be. any ideas on fixing this? It only happens with leonardo.
24  Using Arduino / General Electronics / Re: building an AC rectifier on: December 09, 2013, 04:15:37 pm
FYI - you can buy a bridge rectifier that has 4 diodes in one package with 4 terminals.  Building one yourself is a good learning experience, but I can't remember the last time I built built one.

Also, it's a good idea to "derate" you components.    The voltage rating on your 1N4007 is fine, but at 1 Amp, you are pushing it to it's limit.    When you first power-on, you will likely get quit a bit more than 1A of "inrush" current  as the capacitor charges-up.    Your diodes will probably survive, but it's good to have some safety margin.   (I haven't checked the specs, but they probably can withstand more current for a short time.)

ahh, wish I would have known that! it was indeed good learning experience though.
25  Using Arduino / General Electronics / Re: building an AC rectifier on: December 09, 2013, 01:00:08 pm
Quote
the input is coming from a 12v 1A 12w ac adaptor

Such a device is almost certainly going to be supplying you with DC,  not AC.

nope. definitely AC.
26  Using Arduino / General Electronics / Re: building an AC rectifier on: December 08, 2013, 03:45:14 pm
ah I think you're right. I am still new to reading schematics, but this seems more correct, maybe?

https://www.dropbox.com/s/xbwbhmbz054pzb4/photo2.JPG
Yes looks a lot better to me as well.
Where is the AC coming from?
That is a 35V working capacitor so the maximum RMS AC you should be using is 24V.

not sure if you're asking about what I posted in first part but it is a  12v 1A 12w ac adaptor, so there is already a transformer.

I tried it out and it seems to be working correctly I now have a DC voltage.
27  Using Arduino / General Electronics / Re: building an AC rectifier on: December 08, 2013, 02:40:15 pm
ah I think you're right. I am still new to reading schematics, but this seems more correct, maybe?

https://www.dropbox.com/s/xbwbhmbz054pzb4/photo2.JPG
28  Using Arduino / General Electronics / Re: building an AC rectifier on: December 08, 2013, 02:33:44 pm
Doesn't look right to me. Where is the AC input? It should go to the junction of the diodes with opposite connections. That is the DC comes from the pair of anodes, and pair of cathodes joined and the AC goes in the other pair where an anode and cathode are joined.

Draw us a schematic of what you are trying to make.
ac input is the black and red wires. Though I think it doesn't matter with AC...?

this is what I am trying to build
https://www.dropbox.com/s/gn5mij3fa0d2v4x/Screenshot%202013-12-08%2014.39.12.png
29  Using Arduino / General Electronics / building an AC rectifier on: December 08, 2013, 02:10:05 pm
I want to make sure I am not doing something silly and blow something up smiley if someone can confirm this is correct I would greatly appreciate it. I am mostly worried about the capacitor.

the diodes are 1n4007 and the input is coming from a 12v 1A 12w ac adaptor
https://www.dropbox.com/s/z6ntr9ogph1tkvq/photo.JPG
30  Using Arduino / Sensors / Re: Capacitive Touch Piano on: December 04, 2013, 01:18:38 pm
I cant see any sensing plates in your diagram.
The capsense library relies on a fairly large area of sensing plate to work properly.
If the plate is too small, the capacitance change becomes too small to detect.


actually that isn't true. I've done it with just wire and resistors. so that should work. mostly depends on the resistor value, you can increase it and wires alone will work, but even smaller value ones will work after a certain amount of pressure.
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