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Thread: TTL-driven relays?

  1. #1
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    Default TTL-driven relays (or other suggestions for triggerering GM-20 with TTL)?

    Does anyone have any recommendations for specific relays (or specifications) that could be driven directly by a 5-volt TTL/Shutter signal?

    I lieu of that, any recommendations for a basic driver circuit that will allow TTL signals to drive your basic Radio Shack-variety 12VDC relay?

    Thanks!

    Randy
    Last edited by Stuka; 09-01-2007 at 05:21.
    RR

    Metrologic HeNe 3.3mw Modulated laser, 2 Radio Shack motors, and a broken mirror.
    1979.
    Sweet.....

  2. #2
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    What do you need a relay hooked up to the shutter for? Perhaps there is a better way to do what you need to do
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  3. #3
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    I need the exact same circuit to turn on a lumia wheel motor and stuff like that.

  4. #4
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    I'll probably use a GM-20 as my "shutter" device since is will spring-return to an "off" position. I figure it would be easiest build a fixed-voltage driver for the GM-20, and activate that circuit through a TTL / 5volt relay (or relay+driver circuit). I want to be able to trip the same relay (OR the GM-20 driver circuit directly) with other 5-volt inputs from case interlock switches, remote shutter safety switches, etc.

    I can build from schematics, but my knowledge base is somewhat lacking when it comes to circuit design skills!
    I am DEFINITELY open to suggestions for this, and really want to keep everything as simple as possible. If anyone has a recommended solution (with circuit examples), I would really like to hear from you!

    Thanks!
    Last edited by Stuka; 09-01-2007 at 05:09.
    RR

    Metrologic HeNe 3.3mw Modulated laser, 2 Radio Shack motors, and a broken mirror.
    1979.
    Sweet.....

  5. #5

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    Three possible circuits to apply in some way:

    Level converter:
    Use an n-channel JFET, gate to common ground, pull-up resistor on the drain to 12V, input to the source. Anything over 1 to 2V input should be fine. Buffer that voltage (current gain) for driving the relay.

    Direct relay drive:
    MOSFET, like IRF630 or similar, where 5V on the gate is enough to drop the channel resistance from >300M to <1R, place the FET on the ground side of the 12V relay coil. This also does your 5V to 12V level conversion.

    Simple buffer without level translation:
    Hex inverting buffer, put signal in one of the 6 gates, output feeding the other five inputs, common the outputs of those 5 gates to drive a 5V relay. A 12V capable CMOS logic IC with the JFET trick on the front end can convert from 5V TTL for a 12V relay.

    Whether you choose the MOSFET or the hex inverting buffer might mostly depend on the drive current you need, as well as what's in the junk box.
    Last edited by The_Doctor; 09-01-2007 at 05:24.

  6. #6
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    Unfortunately, my junk box doesn't contain much more than a few relays and some hook-up wire (remnants of another expensive hobby in model railroading!). Anything I put together will require at least one trip to Radio Shack, so I can already tell this hobby is going to "nickel and dime" the personal hobby fund into oblivion!

    Another option I was wondering about (and again, open to suggestions here) is directly driving the GM-20 from a 5-volt shutter / TTL signal, without bothering with the relay. I need just enough "on-off" movement out of the GM-20 to allow it act as a beam shutter device, nothing else.

    Any and all help is appreciated - including circuit examples, since I know what a transistor is, but clueless on how to use one without a schematic!

    Thanks again!
    RR

    Metrologic HeNe 3.3mw Modulated laser, 2 Radio Shack motors, and a broken mirror.
    1979.
    Sweet.....

  7. #7

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    The parts I mentioned are so simple you'll figure it out even without the circuit examples, just look up their pinout diagrams and you're in business. I described the JFET pin connections already, the inverting buffers are easy, and the MOSFET needs input on gate, current from supply through load into Drain, Source to ground. The data sheets have enough diagrams to remind you what goes where, these are very simple circuits..

  8. #8
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    Randy,

    For driving GM20's, there are better methods than using a relay. PM me your email address, and i will email you a PDF of the circuit i use to drive GM20's and the like. This one uses a TDA2040, and provides damping( not that damping is really needed for a shutter )

    David
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  9. #9
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    Another option I was wondering about (and again, open to suggestions here) is directly driving the GM-20 from a 5-volt shutter / TTL signal, without bothering with the relay.
    Hey Stuka, you can hook it up this way, but unfortunately the GM-20 draws a whole lot more current than a TTL driver can source. There are several ways to do it, the way I typically use and currently have setup in my current projector, is through a relay. I'll see if I can't draw something up and send it to you. Basically, you can use a 12V relay and use a simple 2n2222 transistor as a switch to drive the 12V relay. Or you can just use a 5V relay but you will still need a transistor switch to drive the current that the relay will need to energize. You will want to make sure you have a diode in reverse on the output of the transistor as the relay will blow it eventually with reverse EMF as the magnetic field collapses on the relay coil. You know, if you end up making it to FLEM or SELEM or whatever, if you bring all you stuff I'd be happy to help put it together with you.

  10. #10
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    Thanks for all the input, guys!
    This is DEFINITELY a hobby that puts those dormant brain cells to use!

    Dave - PM heading your way!

    Randy
    RR

    Metrologic HeNe 3.3mw Modulated laser, 2 Radio Shack motors, and a broken mirror.
    1979.
    Sweet.....

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