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16  Using Arduino / Sensors / Re: Measuring the resistance and thus temperature of an RTD on: May 07, 2013, 01:11:05 am
Thanks for the help magician
17  Using Arduino / Sensors / Re: Measuring the resistance and thus temperature of an RTD on: May 06, 2013, 07:37:04 am
Magician could you please explain to me the term OPA and the table you posted below?
Thanx again
18  Using Arduino / Sensors / Measuring the resistance and thus temperature of an RTD on: May 06, 2013, 02:54:30 am
I have a soldering pencil which has an integrated PTC RTD built in. The temperature of the RTD can be represented using this equation y = 0.0056x^2+4.9382X-239.43 where x is the resistance of the RTD and y is the temperature in Celsius. The resistance would vary from 50 to 100 ohms (its a relatively low resistance for an RTD).

Could you please provide me with a way to measure the resistance of the RTD giving the greatest resolution to the arduino measuring it? (ie use all 1024 voltage levels measured with the arduino's analogRead() )

Thank you in advance.
19  Using Arduino / General Electronics / Re: Rectified vs Unrectified AC and power delivered to load question on: April 16, 2013, 02:00:12 pm
Thanx for the help Keith
20  Using Arduino / General Electronics / Re: Rectified vs Unrectified AC and power delivered to load question on: April 16, 2013, 12:43:23 pm
Keith i think you got the equation wrong. Check the link out.
http://www.electronics-tutorials.ws/diode/diode_6.html
"Vripple = (Iload)/fc
Where: I is the DC load current in amps, ƒ is the frequency of the ripple or twice the input frequency in Hertz, and C is the capacitance in Farads.

The main advantages of a full-wave bridge rectifier is that it has a smaller AC ripple value for a given load and a smaller reservoir or smoothing capacitor than an equivalent half-wave rectifier. Therefore, the fundamental frequency of the ripple voltage is twice that of the AC supply frequency (100Hz) where for the half-wave rectifier it is exactly equal to the supply frequency (50Hz)."
21  Using Arduino / General Electronics / Re: Rectified vs Unrectified AC and power delivered to load question on: April 16, 2013, 11:24:52 am
I am kind of confused now with the coefficient of f. You said that f is the frequency of the power line. If the frequency of the AC waveform is 50 hertz then shouldn't the frequency of the fully rectified waveform be 100 hertz? Why is it 200 as you suggest? Please explain.
22  Using Arduino / General Electronics / Re: Rectified vs Unrectified AC and power delivered to load question on: April 16, 2013, 11:14:06 am
Keith i am aware of this equation: C = I/(2FV){where C is the capacitance in farads, I is the current in amperes, F is the frequency of the wave and V is the voltage ripple] , which is essentially the same as your equation. I used 2FV though and you used 4FV. Why is that? 

Thank you both of you for your help btw.
23  Using Arduino / General Electronics / Rectified vs Unrectified AC and power delivered to load question (ANSWERED) on: April 16, 2013, 09:30:30 am
Lets say i have a transformer putting out 11.4 volts AC at a max of 10 amperes. I connect it to a bridge rectifier and therefore the voltage drops down to 10 volts dc (2 x diodes of 0.7 forward voltage drop each). I have a heating element of 2 ohms whose resistance stays constant with temperature (lets just assume that) . If i connect a smoothing capacitor bank on the output of the bridge rectifier and connect the resistor in parallel will more power be delivered to the resistor when compared to:
>the same resistor connect to the AC 11.4 volts?
>the same resistor connected to the 10 volts dc without the smoothing capacitors?

Thank you very much for the help
Regards Void
24  Using Arduino / Sensors / Use of a finger as a (touch) button by passing current thtough it? on: April 12, 2013, 03:28:59 pm
Hello people,

I am trying to use my finger as a button. I am using two contacts one being the ground, and the other one being connected to the arduino's digital input along with a pullup resistor.  I very roughly calculated my finger's resistance and its in the range of megaohms at 5volts (around 2.5Mohms). The problem is that at that kind of resistances, the pullups must also take huge values (>6 Mohms) in order for the pin to go low. This method also implies noise.  Is there a better way to do this? Enlighten me please smiley

Thank you in advance
Have a great great day
Void
25  Using Arduino / LEDs and Multiplexing / Re: Ghost LEDs? Weird phenomenon happening to my white leds :O on: March 27, 2013, 10:17:06 am
My soldering iron is not earthed. It's got a three prong british plug but the top prong (earth) is not connected to anything. Only the live and neutral wires leave the plug to go to the soldering iron.
26  Using Arduino / LEDs and Multiplexing / Ghost LEDs? Weird phenomenon happening to my white leds :O on: March 27, 2013, 12:24:48 am
I was soldering an led array yesterday. It's made up of 5 rows of white leds connected in parallel via a single 5 ohm resistor to ground. Each row consist of 4 leds connected in series. I got an AC soldering iron. 30 watt, 240 volts, 50 hertz. As soon as i touched the leads of the leds with my bare hands while in the array and touched the soldering iron tip on the other side of the array, some of the leds would very dimly light up.

Do you guys have a clue why this is happening?

Thank you in advance

Additional:
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The leds light up even brighter when one side of the array is connected to earth via a 3 pin UK socket without the need of me touching the connections with my bare hands
27  Using Arduino / Motors, Mechanics, and Power / Re: How do you find the power output of an unknown transformer?? on: March 21, 2013, 10:31:58 am
Thank you very much people smiley
28  Using Arduino / Motors, Mechanics, and Power / Re: How do you find the power output of an unknown transformer?? on: March 17, 2013, 03:07:44 pm
Mr pancake could you please provide me with such information? (a link maybe? )
Thanx
29  Using Arduino / Motors, Mechanics, and Power / Re: How do you find the power output of an unknown transformer?? on: March 17, 2013, 02:16:53 am
Thanks MarkT
The transformer is labelled 3-246
I attached some images
30  Using Arduino / Motors, Mechanics, and Power / How do you find the power output of an unknown transformer?? (SOLVED) on: March 16, 2013, 03:43:46 pm
I got this one transformer. It's pretty small in size.The transformer's secondary output is center tapped. It will take in 240 volts and spit out 9volts on two different (yellow) cables when measured from the third cable(ground) and 18 volts when the PD is measured between the two (yellow) cables .

My question is: Is there a way to find out the maximum safe current of the secondary winding of this  transformer and therefore its power output?

Thank you in advance
Void
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