Relay triggering a laser... need help.

Discussion in 'Analog & Mixed-Signal Design' started by jkjome85, Jul 20, 2016.

  1. jkjome85

    Thread Starter New Member

    Jul 20, 2016
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    I could use some guidance:

    I have a laser that I want to be able to turn on/off using a camera intervalometer to trigger it. I imagine that the intervalometer would produce the signal to trigger an electromagnetic relay, and that relay would be connected to the power supply of my laser to turn it on/off. Using an intervalometer would allow me to program the frequency that the laser is triggered on/off, as well as how long the laser stays on when triggered.

    My Neewer Intervalometer ( https://www.amazon.com/Neewer-Shutter-Release-Remote-Control/dp/B003Q9RERY ) has a stereo (3 pole) 2.5 mm jack plug. I connected my multimeter to the jack in between the tip (shutter release) and the ground (base sleeve). When the intervalometer is trying to trigger a camera to fire, the voltage reads 0.2v. When the intervalometer is not trying to trigger a camera to fire, the voltage reads 0.8v.

    What kind of a circuit do I need to build so that my intervalometer can trigger a relay? I know that I cannot directly power a relay using the very low voltage coming out of the intervalometer’s 2.5mm jack plug. I think I need to boost the voltage coming out of the intervalometer’s jack plug, but I am not sure how. Also, while my multimeter is reading 0.2v, I think it is suppose to be 0v when it is trying to trigger a camera to fire (according to Canon cameras). So, I think that I would have to use a Normally Closed Relay, so that when the intervalometer is trying to trigger the camera (or laser) to fire (0v), then the relay allows power to pass into my laser to turn it on.

    Any assistance is much appreciated!
     
    Last edited: Jul 20, 2016
  2. BR-549

    Well-Known Member

    Sep 22, 2013
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    I would do more research first. That unit has two poles, I believe, one for auto focus and one for the snap.

    Verify the snap pole. Try to get prints of unit or camera. I would guess that the snap pole is just a continuity switch. We need to verify.

    Can you measure the voltage at the receptacle on camera? Also during manual camera snap?

    Let's verify the snap pole function.
     
  3. Kjeldgaard

    Member

    Apr 7, 2016
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    The timer is certain with two open collector outputs - the Amazon description says:
    "Full functions supported as the camera shutter switch (with halfway or complete pressing)"

    I own both a wired and a RF-wireless remote, for my Canon EOS 60D camera. And when I get home later, I will check voltages and connections in the jack connector.
     
  4. jkjome85

    Thread Starter New Member

    Jul 20, 2016
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    So, I connected a cable to my DSLR camera's remote input, so that I could take voltage measurements. When the camera is not taking a photograph, the voltage reads 3.18v. When the camera is taking a photograph, the voltage reads 0.00. (Measurements were taken between the tip (shutter release) and the ground (base sleeve). The middle sleeve is for the auto focus, or to wake the camera up when you halfway press the shutter button... which I assume I can omit in my circuit design, since I will be triggering a relay and not a camera).

    I also found more information about Canon's remote trigger input here. It discussed the electrical characteristics:

    http://www.doc-diy.net/photo/eos_wired_remote/
     
  5. BR-549

    Well-Known Member

    Sep 22, 2013
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    Then all that's left is deciding if you want a high side switch or a low side switch.
     
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  6. jkjome85

    Thread Starter New Member

    Jul 20, 2016
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    BR-549,
    I am not familiar enough to know which is best (high side or low side switching) for this application. Would my circuit use a MOSFET?
     
  7. BR-549

    Well-Known Member

    Sep 22, 2013
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    jkjome, I wouldn't know. I don't know your circuit.

    Search, read and study "high side and low side switches". They are not hard to understand and there are many examples.

    It will depend on your application of your laser circuit. Your intervalometer will control the switch, not act as the switch.
     
  8. jkjome85

    Thread Starter New Member

    Jul 20, 2016
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    I created a wiring diagram for my circuit. I am new to electronics, so there are likely errors to my design. Any feedback is much appreciated as I begin to learn the function of these components. Laser Relay Circuit 1000x956.jpg
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Pretty good so far. A couple of things...

    With only 3 V available for gate drive you will need a logic level FET. Also, you should have a large value resistor from the gate to source to guarantee turn-off.

    Also, is there a reason for the relay? In other words, can't the laser and its trigger mechanism be powered by the same 3 V battery? If so, there is a good chance that you can eliminate the relay and have the FET switch power to the laser.

    ak
     
  10. jkjome85

    Thread Starter New Member

    Jul 20, 2016
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    To make sure I understand what you are saying... I need to use something called a Logic Level N-channel MOSFET Transistor? (I'm still learning my transistors).

    Please view the revision to my wiring diagram to see if I understood this correctly.

    I understand what you are saying here, and that would work for this 3v laser, yes. But, I would like to be able to use this circuit to occasionally turn on/off other devices (like 12v lights) instead of just the 3v laser. By incorporating a relay, I would be able to swap out the 3v battery for a 12 volt battery, and the 3v laser for a 12v light.
    Laser Relay Circuit 2 1000x956.jpg
     
  11. Kjeldgaard

    Member

    Apr 7, 2016
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    It seems that there is a solution to the task already, and they fit with my measurements:

    CanonEosRemote-1.jpg

    However, I have just a few comments on the schematic in post # 10. There lacks a fly-back diode across the relay coil, and I would also protect the gate of the MOS transistor - maybe just 10K ohm resistor in series with the gate.
     
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  12. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Yes, "logic-level" is a category of MOSFETs.
    The 1 K should be much larger, like 100 K.
    Most power MOSFETs have a max Vgs of 20 V, and the drain voltage rating can be over 1000 V, so a single circuit that works with anything from 3 V to 15 V is very doable. If you want to stay with the relay, add a diode across the coil as mentioned above.

    OK, forget all of that.

    The link in post #4 and the schematic in post #11 bring up a point. If the circuit driving your circuit has an open collector output that goes low to activate the external device, then the logic polarity is backwards and a resistor from the gate to the source is not needed, but a pull *up* resistor to something no greater than 3.3 V is needed. This makes things a bit more complicated. P-channel MOSFETs usually do not have the guaranteed low Vgs performance of logic level N-channel devices, and you will need a level shifting stage when working with 12 V devices.

    If you have a relay that will activate with only 3 V across its coil, then the thing to do is change the N-channel MOSFET into a PNP bipolar transistor such as a 2N3906 or 2N4403. I'll see if I can whip out a schematic.

    ak
     
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  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    First pass at a schematic. Left side is relay output, basically your schematic corrected for the logic polarity. Right side is an all transistor version, no relay. It can be adapted to a FET output stage that eliminates R5. all circuits should be good for 100-200 mA of laser component current.

    ak
    LaserTrigger-1-c.gif
     
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  14. jkjome85

    Thread Starter New Member

    Jul 20, 2016
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    AnalogKid- your schematics are very much appreciated, thank you.

    "all circuits should be good for 100-200 mA of laser component current."..... this only applies to the schematic on the right, correct? As I understand it, the schematic on the left would require a power source to be connected in series with my load (laser, light, etc), along with the relay (like the schematic I drew up). That would be good, so that I can swap out a 3v battery/3v laser, for a 12v battery/12v light, and change what this circuit controlls.
     
  15. jkjome85

    Thread Starter New Member

    Jul 20, 2016
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    Will the schematic on the left require a fly-back diode across the relay coil like comment #11?
     
  16. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Yes to the diode. Here is a non-relay version that is good for a wide range of laser device voltages.

    ak
    LaserTrigger-2-c.gif
     
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