Connecting this switch to a 9V battery

Discussion in 'General Electronics Chat' started by Dawud Beale, Jan 2, 2013.

  1. Dawud Beale

    Thread Starter Member

    Feb 10, 2012
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    I'm pretty new to practical electronics and am a bit jumpy about soldering, connecting stuff up etc after seeing how a 9V battery can cause an LED to explode without a limiting resistor.

    I just soldered this switch to a battery holder and put a 9V battery in and the switch lit up without me connecting it to anything else. does it have internal resistance and is it safe?

    http://www.sci.com.tw/PRODUCTS/switch/(R13) PUSH SWITCH/R13-508.htm
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I'd doubt the switch has a resistor in it (maybe..can't tell from that datasheet).. A simple resistance test with a multimeter will answer that for you.
    A 9V battery (and any battery) has its own "internal resistance" in it. This is how many of the cheap LED toys get away with just a battery and LED (no resistor)
     
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  3. Dawud Beale

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    Feb 10, 2012
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    why does it light up when I connect the negative and positive terminals to the 9V battery though? It lit up for a few seconds then went dead so I might have killed it, but I don't see how your supposed to connect this to a battery without shorting it.
     
  4. mcgyvr

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    ah yes now we get the missing info.. you never said it went dead before.
    Yes you simply destroyed the LED.

    You need a resistor (330ohm or 360 ohm 1/4 W)in series with the LED to limit the current from the 9V battery.. try again..
     
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  5. tracecom

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    Apr 16, 2010
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    Yes, you likely ruined the LED. Which version of the switch do you have?
     
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  6. Dawud Beale

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    Feb 10, 2012
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    how is it possible not to ruin the led though as its inside the switch and i never even connected the whole switch in a circuit. i just connected the positive and negative terminals to the batteries, i had intended to connect an led and resistor to the terminals. do i only need to use two terminals on the switch? have i effectiveley short circuited the switch?
     
  7. mcgyvr

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    What? Your switch has 4 posts correct.. 2 are the switch and 2 are the pos/neg of the LED.
    All you did was blow the LED due to overcurrent.. Its now dead. When you get a new switch put a resistor (as I stated above) in series with the switches LED and it will all be fine.
    The usually don't include the resistor in the switch to allow the end user to use whatever voltage they have available to power the LED (with the proper current limiting resistor in series of course)
     
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  8. Dawud Beale

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    Feb 10, 2012
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    ok thats weird. so basically I connected up the LED's instead of the actual switch terminals. the LED posts had a + and - on it so I assumed I connected it from there. Most confusing. Are the four posts connected electrically? wont that in essence mean that the LED will always be on and drain the battery if its connected independently from the switch? The datasheet never gave me all of this info, how was I supposed to get all this from the data sheet?
     
  9. Leigh

    Member

    Feb 11, 2010
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    The data sheet has most of the info you need. It just does not teach you how to use it. It is because you are new to electronics that you are having trouble. Therefore you need to think hard and test things before proceeding. You need a multi meter, and need to know how to use it. You also need to know Ohm's Law. The Sticky explains this, and how to use LEDs, beautifully.

    The data sheet shows different versions of the switch. All except type A and B have a LED inside. Types CL and DL seem to have a resistor in series with the LED. What value the resistor is isn't mentioned. So put a variable resistor (say 1k) in series with the LED terminals. Connect the 9V battery and your multi meter in series also, and measure the current as you wind the resistor down from 1K. Probably the LED won't light up until you wind the resistor down a way. Stop when the current is about 20mA. Then measure the resistance of the variable. Then you can calculate the value of the internal resistor. For the switch versions without an internal resistor, apply Ohm's Law to find the value resistor you need.
     
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  10. mcgyvr

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    What is the exact part number of the switch you have?
     
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  11. Dawud Beale

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    Feb 10, 2012
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    3a125vac
    1.5a250vac
    r13-508
     
  12. Dawud Beale

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    Feb 10, 2012
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    I have a multimeter and know Ohms law. I also know about LED's and limiting resistors.

    I am actually a second year Electrical and Electronic Engineering student at University believe it or not, but I'm only just starting to get into some hands on practical stuff at home, so far at Uni its mainly been maths, programming, embedded systems with a PIC, digital theory and practical using ISPLever, ABEL and GAL devices, PLC's, semiconductors, etc etc so there hasn't been a great deal of practical yet, we've done some but I still am not very confident at going and buying a load of stuff at Maplins and just having a go at stuff.

    I have a Lab at home now with all the kit I need, anything I'm short of I can buy straight away as well.

    Not done a great deal of electronic practical but obviously I will need it in the work place so trying to build up those skills myself at home.

    I'll buy another one tomorrow as it seems I've blown the one I bought, hope I don't make too many mistakes as it involves my own GAL IC, a 555 timer, 9V battery, voltage regulator etc so cant really mess up any of the components.
     
  13. tracecom

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    In order to determine the part number of the version of the switch you have, you must look at the datasheet and compare the options available to those present on the device that you have. Then use that information to complete the part number in the format, R13-508xxx-xx. Until you determine the part number and convey that information to the forum, you won't get any specific help.
     
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  14. mcgyvr

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    R13-508 is only part of the number.. the "function" , "button" , and "terminal" portions are not included.. (we really only need the function part to help)
    It should be something like R13-508AL2-05


    Having hands on experience is what makes a good EE. So keep it up. (its very rare)
    You can learn more with a $50 200 in 1 electronic circuit kit in a weekend than $15k in college education gets you.

    You've already experienced the "destroy an LED" part.. :) Now a few transistors and electrolytic caps and you're really learning :)
     
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  15. Dawud Beale

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    Feb 10, 2012
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    Haha thanks.

    Unfortunately the full part number displayed on the component is what I've typed in.

    Is there any information that will help determine exactly what part it is?

    Can you explain exactly what the function number is as I am not familiar with the methodology for understanding part numbers, I didn't know you could extract that sort of information by looking at the part number.
     
  16. Dawud Beale

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    Feb 10, 2012
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    Ah I have had another look at the data sheet and see what you mean now.

    As the device doesnt display any info on the functions, is there any way for me to determine this from looking at it?
     
  17. Leigh

    Member

    Feb 11, 2010
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    I wasn't intending to be insulting. I didn't take enough notice of the word "practical" in you original post.

    Which switch do you have? I'd say a type AL or BL, 'cos the LED is now blown (no internal resistor). The receipt for the switch might have the full part number on it. How will you know which type you are buying to replace it?

    Of course, you still have a functioning switch, just with no internal illumination. An external LED can serve the same purpose, 'though not as neatly.
     
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  18. mcgyvr

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    A multimeter set to read resistance (and the diode check function will help too for the LED pins) will tell you everything you need to know about the switch.
    There are NUMEROUS tutorials out there on how to use a meter.
    You simply need to check each terminal to the others and see what has continuity and whats happening when the button is pressed (momentary or not,etc...).

    But yes as you have destroyed an LED already your choices from the datasheet are limited down now to one with an LED and no resistor. (you have to zoom in on that datasheet to see the resistors)
     
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  19. Dawud Beale

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    Feb 10, 2012
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    It's ok I never took it as insulting.

    I am still trying to determine which switch I have unfortunately. i just bought a few more but there is no part number on it beyond the generic part number.

    But I guess the main thing is that I know which connections are for the LED and which are for the swicth, I take it they are electrically seperate connections? Also I guess sort of reasonable limiting resistor shoudl do it right? As my circuit will have lots of resistors and things in it anyway, wont that do the trick?
     
  20. Dawud Beale

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    Feb 10, 2012
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    Yeah I know how to use the diode function on my multimeter but what am I looking for exactly?
     
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