Easy Question for You Guys I'm Sure (#001)

Discussion in 'General Electronics Chat' started by olnoob, Jun 26, 2013.

  1. olnoob

    Thread Starter New Member

    Jun 26, 2013
    OK. 42 year-old newbie here. Dad was an electrician and I grew up helping wire buildings. Built some simple electronic stuff as a kid. Never took a class or learned what a crystal is. Just last week became down with diodes. Basically, when it comes to electronics I'm a 6 year-old. But now I'm fulfilling a lifelong dream of building a coin-operated video arcade in my home (I currently have 29 complete machines and 17 circuit boards) and I'm presently realizing the need to build and customize testing equipment and I'm going to be posting some ignorant questions. I hope this is the place. If not please feel free to point me in the right direction.

    Thank you.

    OK. I bought a 5v DC relay at Radio Shack. The schematic printed on the back looks like this:

    Relay Schematic 01.png

    I research and see that the symbol in the lower left means "induction coil". I think I get it. Running a circuit through the coil creates a magnetic field that moves the arm AWAY from the coil. The image shown is resting state, during which time whatever current is terminated in the lower right [marked "source" on the following diagram] will pass through to that terminated at the upper left [marked "A"]; activating the relay (by applying 5v and Ground to the coil) will break the aforesaid connection and move the source current to that labeled "B".

    Relay Schematic 02.png

    Am I right? I want to be sure before I solder this thing in.

    Also, will wiring the coil backwards have any effect on the magnetic field it generates, rendering this thing inoperable? And, if so, then what goes on the left, 5v or ground?

    Any help very much appreciated.
  2. gerty

    AAC Fanatic!

    Aug 30, 2007
    Looks like you have it figured out. Reversing polarity will not have any effect on it.
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
    I think you have it. Normally the coil is not polarized, wire it either way.
  4. MrChips


    Oct 2, 2009
    1) When requesting help on a component it helps to give us the brand and model number. It should be written on the relay.

    2) It should not matter which way you connect to the relay coil.

    3) When the coil is energized, it will attract the armature, i.e. it should move towards the coil.

    4) Regardless of what is printed on the back, take an ohmmeter and determine which two contacts are shorting when the relay is not energized.
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Yes, in general you are right.

    In simple terms, running 5 volts dc through the coil will cause the switch to move.
    You will always use the switch terminal you labelled "source". Then you can use either of the other two poles but it depends if you want the other end connected or disconnected as the default (normally closed, or, normally open ).

    As for the coil, it doesn't matter which direction the current flows because you will either make a magnetic north or South Pole. The steel allow it attracts will still be attracted.
  6. LDC3

    Active Member

    Apr 27, 2013
    You got a good start at deciphering schematics. The one thing that might not be correct is that the switch is usually a metal plate which is held in place by a spring. When the coil is energized, it pulls the switch to the second position. The diagram would become chaotic if the switch is reversed leaving A and B in the same position. They want to show the results as simply as possible (it does not matter what is happening inside).
    It should not matter which way the coil is connected since there is no polarity marked on the diagram.
    Also the 'source' need not be the source. It could be A and/or B. It is usually marked 'common'.
  7. ifixit

    Distinguished Member

    Nov 20, 2008
    Welcome to AAC,

    Your description of a single pole, double throw relay is basically correct. However, the armature is drawn toward the coils magnetic field when 5V is applied, so the diagram doesn't show that correctly and it usually doesn't matter to the user anyway so long as the switching happens as expected.

    Try it out on the bench so you can see for yourself how it works. The polarity of the coil current doesn't matter, it should still switch as expected.

    Have Fun,
  8. olnoob

    Thread Starter New Member

    Jun 26, 2013
    Very grateful to all of you.

    Keep on the lookout for me please. I know I'll never be an expert at any of this but I'm having a lot of fun learning it, slowly but surely. Electronics really is one of the most fascinating and useful fields in the universe.
  9. sheldons

    Well-Known Member

    Oct 26, 2011
    heres a way to drive your relay as an example-you need to select the relay type with the correct coil voltage 12v-5v etc and away you go.....
  10. atferrari

    AAC Fanatic!

    Jan 6, 2004
    I can see you plan to ask up to 999 questions. :eek:

    Am I right?

    Hope I could answer just one of them in the future...

    Buena suerte.
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Come on, this is an electronics forum. When the OP said,
    He was using binary:D
  12. atferrari

    AAC Fanatic!

    Jan 6, 2004
    For a moment I wondered octal or hex! :p