Home     Contact     Forum     Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science     RSS     Terms of services     Privacy policy  
   
 Home     Forum     Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science   

Author Topic: portable LED home position indicator  (Read 5132 times)

0 Members and 1 Guest are viewing this topic.

Alex Robson

  • Guest
portable LED home position indicator
« on: May 22, 2011, 12:52:42 PM »
Hi everyone
                 Help is needed in My project  I wish to make up a portable type LED home position indicator  I want to use 10 LED's independent of each other  each LED to light up when the home position is reached That would complete each circuit
  I have a 12VDC supply  red LED  2.2vf  20if   the most important part is missing  the best way to build it  If these parts can be used great but not important
Thank you
Alex Robson
                        (the indicator LED control box is about 3 feet  ( 1 meter ) away from the home positions and will wiring  to each home position)

kam

  • Administrator
  • Hero Member
  • *****
  • Posts: 1849
Re: portable LED home position indicator
« Reply #1 on: May 22, 2011, 21:15:03 PM »
hello Alex,
to tell you the truth, i did not understand what you want to make. What is home position? What you wan to make?

Alex Robson

  • Guest
Re: portable LED home position indicator
« Reply #2 on: May 23, 2011, 03:55:35 AM »
Hi
    What I mean in homing devise is  it would operate like a limit switch  the circuit would be open until it was touched  and then supply power to a led
      one side the led wire is connected to a insulated brass pin  when touched in would  close the circuit   down to earth  anyway that was hoping
                       have a great day
                      Alex

_pike

  • Administrator
  • Full Member
  • *****
  • Posts: 182
Re: portable LED home position indicator
« Reply #3 on: May 23, 2011, 10:34:51 AM »
Still i cannot understand you........."it would operate like a limit switch" To what??????? You want to make a touch switch as far as i can understand and when touched in would  close the circuit the led pin?????

Alex Robson

  • Guest
Re: portable LED home position indicator
« Reply #4 on: May 24, 2011, 09:59:04 AM »
hi
    My project requires 10 LED arrays of a single LED  I have 10 red LED 2.2fv 20mA and I have a 12VDC supply I would like to know the size of each resistor     In engineering we use a  electronic edge finder    it is a instrument that can  locate edges of work pieces    It is battery operated  when the insulated ball touches the work piece it lights up a red  LED in the body
My project is  10LED in a control box and wires running to a insulated brass contact in a  work piece holding device  when the work piece touched the brass block the  circuit is closed  the led lights up   
 To sum things if you can tell me the resistor size for each of the 10 single arrays  and if my 12   Volt DC output current is 200mA is suitable   hopefully this makes sense to you all  I'm sorry to be a pest
Thank you very much for time
Alex 

_pike

  • Administrator
  • Full Member
  • *****
  • Posts: 182
Re: portable LED home position indicator
« Reply #5 on: May 24, 2011, 13:22:31 PM »
If the leds are connected in paraller mode then you will have to use a 50Ohms 4watt.But most arrays(strips) have already resistors on them to give 12v direct...So if you plan to make an array use the values above.....If you want to use the series method then you will have to increase the voltage so.........
« Last Edit: May 24, 2011, 13:24:50 PM by _pike »

kam

  • Administrator
  • Hero Member
  • *****
  • Posts: 1849
Re: portable LED home position indicator
« Reply #6 on: May 24, 2011, 14:17:22 PM »
Quote
My project requires 10 LED arrays of a single LED
10 LED arrays of a single LED? So 10 LEDs in parallel?

In any case, as pike said before, LED arrays which are rated at 12 volts, usually do have limiting resistors already connected. Check this out first.  This means that you will connect all 10 arrays in parallel without an external limiting resistor. The overall voltage to operate is 12 volts, and the total current will be 200 mA

If the LEDs have NOT limiting resistor, then here is what you must do. Each LED has 2.2 forward voltage, so at 12 volts, you can connect 5.45 LEDs. I suggest you connect 6 LEDs in series. Make 2 of these strips with 6 LEDs in series. Each strip will require  13.2 volts to operate (at full brightness) and will draw 20mA. Then connect the 2 strips in parallel. What you will have now is 12 LEDs that can operate at 13.2 volts and will draw 40 mA.

If you power with 12 volts instead of 13.2, then the strips will still operate but the LEDs will be a little bit dimmer. The forward voltage across each LED will be 2 volts (12/6).

Instead, you can connect 5 LEDs on each strip. But then, you will have to add a limiting resistor to drop 1 volt (because 5*2.2=11). The resistor is:
R = U/I = 1/0.02 = 50 ohms. The power that the resistor will have to dissipate is P=IxIxR = 0.02 Watts = 20mWatts. So a 1/4 watt resistor is fine.
Connect one resistor in series with each LED strip. Then connect again these 2 strips in parallel. You have 10 LEDs which will operate at 12 volts and will draw 40 mA.




Alex Robson

  • Guest
Re: portable LED home position indicator
« Reply #7 on: May 26, 2011, 05:25:52 AM »
Firstly I wish to thank you both for time and support  with my project  but I must admit  I'm lost
In my last project 18th of October 2010  Another LED dimmer type project
You suggested to use your Led Array PWM dimmer with the 555 which is great and thank you for that
In  your LED schematics  you have various Arrays, rows and LED using different  size power supplies
now for  my 10 single led project  do different rules apply
I hope this time  you will understand what I require for this project  Say I have 10 LED's  to operate with each having  there own station and each having there own insulated contact when contact is closed or activated it will light up  a LED  then move to the next station and so on  with all 10 LED's
For me to express my thoughts in writing is not so easy for a one finger typist   I'm most great full  for you to spend your time on an old retired engineer with his projects 
thank you I'm truly great full
have a great day
Alex robson

kam

  • Administrator
  • Hero Member
  • *****
  • Posts: 1849
Re: portable LED home position indicator
« Reply #8 on: May 26, 2011, 07:48:06 AM »
I think i understand what you want now Alex. So, each LED must be powered with 12 volts and light independently (no array). As you said, each LED has 2.2 forward voltage drop rated at 20mA. Here is how to calculate the resistor. The resistor must generate such a voltage drop, that the voltage across the LED is 2.2. So, the voltage across the resistor must be 12-2.2 = 9.8. From ohms law:

R = U/I => R = 9.8/0.02 = >R=490. So, as pike said some messages before, a 500 ohms resistor is ok.

Now to calculate the power of the resistor. The power that this resistor will have to dissipate is

P = I2 x R => P = 0.022 x 500 = 0.2 watts = 200 mWatts. So you can use 1/4 resistors, but i would go to 1/2 just to play safe.

So, each LED has to have a series resistor of 500 ohms 1/2 (or 1/4) watts.

If the LEDs light independently through a 10-selection switch (or something), then you need only one resistor 500 ohms 1/2, to connect it to the common cathode of all LEDS. But this is possible only if each LED light independently.

Alex Robson

  • Guest
Re: portable LED home position indicator
« Reply #9 on: May 26, 2011, 11:05:20 AM »
Kam
       Thank you very much that is exactly what I want   and you have made it simple for me to understand  I can now  go ahead with my project   (make up all the parts etc)
  I am most grate full for your advice  Thank you
have great day
Alex Robson