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Thread: How do I switch a 5v supply on/off with a logic 3v?

  1. #21
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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Well according to the datasheet I found here:
    http://search.digikey.com/scripts/Dk...=160-1300-5-ND

    The maximum forward current for the LED is 80mA.

    Pull out the relay and replace it with a 10k resistor. Redo the measurements above. I suspect the LED isn't turning on. Either that or you don't have it hooked up the way that you think it's hooked up.
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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Quote Originally Posted by jes1510 View Post
    Well according to the datasheet I found here:
    http://search.digikey.com/scripts/Dk...=160-1300-5-ND

    The maximum forward current for the LED is 80mA.

    Pull out the relay and replace it with a 10k resistor. Redo the measurements above. I suspect the LED isn't turning on. Either that or you don't have it hooked up the way that you think it's hooked up.
    Here is the datasheet on the exact component I'm using..

    http://www.nteinc.com/specs/3000to3099/pdf/nte3040.pdf

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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Quote Originally Posted by jes1510 View Post
    Well according to the datasheet I found here:
    http://search.digikey.com/scripts/Dk...=160-1300-5-ND

    The maximum forward current for the LED is 80mA.

    Pull out the relay and replace it with a 10k resistor. Redo the measurements above. I suspect the LED isn't turning on. Either that or you don't have it hooked up the way that you think it's hooked up.
    I'm about to scream.. I've not done the 10k trick yet, but, I put a 100ohm and 22ohm resisters inline with the pin 1 and the phidgets.. Toggle it on and off, and I can see the voltage from pin 4 and 5 go from 0 to 5v. I hooked up the relay. (BTW, I've now switched to a independent 5v supply for the relay side) and I now read around 1.1v when across the coils.. I just don't get it.. it's like not enough current is getting through to drive the relay or something...

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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Take a picture and post.

    If you have independent power sources they do need to have a common ground.

    Do you have any common transistor laying around? Just asking to see what you have available.

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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Quote Originally Posted by Quantum View Post
    Take a picture and post.
    Done

    Quote Originally Posted by Quantum View Post
    If you have independent power sources they do need to have a common ground.
    Not with a opto, would defeat the purpose of isolation then.

    Quote Originally Posted by Quantum View Post
    Do you have any common transistor laying around? Just asking to see what you have available.
    Not at the moment..

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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Yea no need for common grounds forget about that.

    You need a protection diode across the coil.

    The opto is still a transitor and it needs to be protected when the coil trips on and off.

    When the coil loses power the magnetic field cause a brief surge and this will damage transistors. The diode will allow this to fade with out damage to transistors or ic.

    It could be that the ISO crapped out on you.

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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Quote Originally Posted by Quantum View Post
    Yea no need for common grounds forget about that.

    You need a protection diode across the coil.

    The opto is still a transitor and it needs to be protected when the coil trips on and off.

    When the coil loses power the magnetic field cause a brief surge and this will damage transistors. The diode will allow this to fade with out damage to transistors or ic.

    It could be that the ISO crapped out on you.
    Well, I did the diode thing.. early on.. pulled it while testing because nothing was working. Why do I get a voltage of 5v when I test it with my multimeter without the relay in place when the opto is toggled on?

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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Am I using a Opto that can handle driving this relay?

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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Yea it should work take a look at this schematic.

    Still need the 330 on pin one.

    You can find the 3904 at radios shack. Usually comes indivisually or in the npn pnp package.
    Last edited by Quantum; 01-18-2009 at 12:08 AM.

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    Re: How do I switch a 5v supply on/off with a logic 3v?

    Quote Originally Posted by Connor View Post
    Am I using a Opto that can handle driving this relay?
    Me thinks: NO (EDIT: without additional components), based on

    Quote Originally Posted by Connor View Post
    .717v with the relay in place and opto activated, 4.98 or so without the relay.
    -.003v with the relay in place and opto unactivated.

    I don't have the diode in place yet, but that wouldn't be the problem.. I can put it in place.. but, I though I would wait till I get this debugged.
    It would appear that your optocoupler is passing the signal, but can't generate enough current to drive the relay. I don't see a "on" current spec'd in the datasheet. I'm not entirely sure - but I think that the "DC CURRENT TRANSFER" of 20% at If=10mA, Vce = 10V means you don't have enough juice to drive the relay. In theory, that limits the output to 20% of 100mA (or 80 as quoted elsewhere), well below 77 for the relay.

    -Fergs
    Last edited by lnxfergy; 01-18-2009 at 12:01 AM.

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