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Using a relay on a WAM board? — Parallax Forums

Using a relay on a WAM board?

Sun1ShineSun1Shine Posts: 10
edited 2005-10-05 16:54 in BASIC Stamp
I have been trying to use a Aromat DS2E-M-DC5V relay ( I have a bunch of them) on my three WAM boards using the 2n3904 NPN, a 4148 diode, and a 10K resister to the i/o pin 14.· It doesn't work.· If I power the relay directly from Vdd and Vss then it works but I can't get the stamp to operate it.

I would like to operate a number of halloween project windshield wiper motors (12v at 2A), ref/ scary terry site.

Any help would be most appreciated...I'm not a electrical engineer.·· If a different relay·must be used, is required instead·(one I can run over to Radioshack to get) let me know....

I have tried all of the WAM experiements and had no trouble running them and making all kinds of mod's but am surprised a relay was not included in the experiments.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-03 15:57
    Hello,

    ·· The 10K resistor is too high to allow the transistor to bias.· Try a 1K instead.· Are you using the Homework Board or the Board Of Education?· Which revision?

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Sun1ShineSun1Shine Posts: 10
    edited 2005-10-03 16:45
    I am using the Homework Board, rev b. I have tried 470ohm, too, but it didn't work.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-03 16:57
    Not sure how you're connecting things.· The Stamp I/O pin would normally go through the resistor (470 ohms is fine) into the base of the transistor.· The emitter would go to ground, and the collector would connect to one side of the relay coil.· The other side would connect to +5V.· Your diode would connect across the relay coil in such a manner that the cathode was on the side of the coil connected to +5V.

    Now for the possible bad news...If you're using Vdd for the supply, you should know that the regulator on the Homework Board Rev B probably doesn't have enough current output capability to run everything you're running.· You should consider running the power devices from a separate power source or Vin.· Or you can upgrade to a board with a beefier regulator on it, such as the Board Of Education.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Sun1ShineSun1Shine Posts: 10
    edited 2005-10-03 17:15
    Everything runs with the relay not connected to the stamp, just powered from Vss and Vdd so it would seem adding the 470ohm resister and 2n3904 and 4148 diode should be okay?

    See the diagram I attached where the relay in the center is shown attached to pin1, D2 I used 4148, the transister is the 2n3904 and the R1 resisters I tried were 10K, 470ohm.· I connected Vcc to the WAM breadboard Vss and gnd to WAM breadboard Vdd.

    The Aromat DS2E-M-DC5V runs at 5v, coil power 400mW, coil 62.5 ohms.
    relay circuit.jpg
    521 x 470 - 83K
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-03 17:28
    I just confirmed that the regulator on that board is only good for around 50mA.· The BS2 is going to take· a few away from that, leaving you with maybe 45mA.· Your relay consumes 80mA of current.· It may be working, but it shouldn't be.· You should definately connect a separate power supply.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Sun1ShineSun1Shine Posts: 10
    edited 2005-10-03 17:33
    Do I just connect the top of the relay to some outside 5v supply and then tie the outside supply gnd to the WAM Vdd?
  • NewzedNewzed Posts: 2,503
    edited 2005-10-03 17:37
    Only if you want to fry everything.· To keep working, connect the outside ground to WAM Vss.

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    Sid Weaver
    Do you have a Stamp Tester yet?
    http://hometown.aol.com/newzed/index.html

    ·
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-03 18:10
    The two supplies need a common ground.· The ground on the Homework Board is the Vss line.· It would connect to the other supply ground.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Sun1ShineSun1Shine Posts: 10
    edited 2005-10-03 18:28
    Thanks! I will try this tonight. I am also dropping by Radioshack and pickup a 7-9V relay with a 18mA coil rating
  • Sun1ShineSun1Shine Posts: 10
    edited 2005-10-04 12:55
    The WAM board can activate a relay with it's own power external to that of the WAM, thanks everyone. Now when my wife gets back from the third Radioshack we are trying to get the 9V 18mA relay from.....
  • Sun1ShineSun1Shine Posts: 10
    edited 2005-10-05 14:27
    Finally figured out a number of things:
    #1. Got ALL the relays I tried - to now work!!!! - directly on the WAM (Homework board): including 4.5v, 5v, and 9v
    #2. I'm an idiot: I have now learned to use Vdd for 5v, Vin for 9v, and Vss for ground NOT visaversa!
    #3. Learned that the relay coils are polarized and will not activate if wired with the wrong polarity (which is not shown on the Radioshack retail packaging....arg)
    #4. Happy Halloween, I'm going crazy with Homework boards, RELAYS!, windshieldwiper motors, Scary Terry Audio Player boards, and skeletons!
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-05 16:36
    That's interesting that the relay was polarized.· The ones Radio Shack carries usually aren't.· In fact most relays aren't unless they have a built-in·Diode.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Sun1ShineSun1Shine Posts: 10
    edited 2005-10-05 16:54
    I got that same result from the 3 relays I tried: AROMAT 4.5v microrelay, AROMAT 5v relay, RADIOSHACK 9v relay.

    Thanks again for your help and giving me a clue! Now you've made me dangerous! Halloween-wise anyways!
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