Running SSR from an existing led circuit

Discussion in 'The Projects Forum' started by blackslide, Jul 15, 2015.

  1. blackslide

    Thread Starter New Member

    Jul 15, 2015
    16
    0
    Hi,

    I'm trying to build an SSR circuit to operate 8 camcorders with a single remote. I was considering
    mechanical reed relays, but since I wanted to keep it simple, (no external psu, etc) I opted for AQY212EH opto mos relays since I thought that the original led current is enough for the relay and a single low intensity led.
    Everything else is sorted but the relays don't seem to work properly.

    I'm using an existing leds current as the control current/voltage for the "control" -side of the relay.
    I cut the original leds common negative/gnd to make it go through my circuit.
    After the relay the control current goes into another led in series (to visualize what channel I'm on), and back to the original negative/gnd.
    The remote signal ~5-8VDC/?mA is going through the "load" -side of the relay. It's a LANC signal (8bit @ ~9600bit/s).

    When I tried to control remote without the relays, (by connecting and disconnecting the wire by hand) it worked.
    but with the relays the remote doesn't work.

    When I use a multimeter to try and measure if the "load" -side is conducting, I hear a buzz instead of the constant beep.
    I was thinking of trying to make the pulse into a constant with a capacitor, but it seems to only charge up and quits conducting afterwards.

    How to get the relay to continuously conduct instead of pulsating? Is there too little current from the control source?
    But the led that is in series is lit up just fine?

    I thought this would be easier, but that's what you get for not fiddling around with electronics more often. :/
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Do you have an Oscope? Likely, the LEDs you tapped into are multiplexed at a rate above your eye's flicker fusion...
     
    blackslide likes this.
  3. blackslide

    Thread Starter New Member

    Jul 15, 2015
    16
    0
    I'd need to test that old junkpile out. Yes I guess they are multiplexed. Would a capacitor not fix this?

    Any good hints on how to execute this?

    We use a controller to control the camera mounts and would like to get the remote functions all into one. It would be great to have just the channels (1-8) to worry about. Thats why we thought we could use the leds as a "control" for the relays...

    The box itself is quite neat :D Hack'N'Slash!
     
  4. blackslide

    Thread Starter New Member

    Jul 15, 2015
    16
    0
    Uh oh, apparently I'd want to bypass the PWM for this IC that the leds go through? SN74LS145

    The leds are organized into two rows of 8leds, first row has a common on pin1 of that IC, second row has a common on pin2... we need a constant unmodulated current from the first eight. But will this even be possible or will it mess up the ability to choose wich led 1-8 is on?

    Any hints on how to do this easier would be more than welcome :)
    Sorry for being a n00b..
     
  5. blackslide

    Thread Starter New Member

    Jul 15, 2015
    16
    0
    Err, I think I might have found a solution.

    Would it help if I control a relay with the multiplexed signal but on the load side I put +9V + cap + resistor.

    Then run that into second relays control side and put the remote signal into that second relays load side?
     
  6. blackslide

    Thread Starter New Member

    Jul 15, 2015
    16
    0
    Hi,

    I've got this far. I've added +9V (actual psu measures 12.35V) and a cap + some resistors. I'm using ancient but good ewb 5.1
    Any help would be appreciated. It would be nice to get "relay 1 load buzz" to actually simulate something pulsing so that the cap
    would work as intended or would it even then work? Does this schematic look sane or does it need changes?
    channel1.jpg

    Thanks!
     
  7. blackslide

    Thread Starter New Member

    Jul 15, 2015
    16
    0
    I've replaced the Relay 1 load buzz with a voltage controlled square wave oscillator, but I'm unable to get the
    "relay 2 cleaned" led to stay on continuously. tried to vary the resistor values and the cap value. Also tried with two caps... :/
     
  8. blackslide

    Thread Starter New Member

    Jul 15, 2015
    16
    0
    Oh, dumb old me. Should a normal low-pass filter work?
    Removing R3 and moving the cap there, maybe 2.2uF and bumping R2 up to 2.2kohm should do the trick?
     
  9. blackslide

    Thread Starter New Member

    Jul 15, 2015
    16
    0
    For some reason it doesn't work. I measured the pulse frequency wih a true rms multimeter, it's 143Hz.
    I used the tools:
    http://sim.okawa-denshi.jp/en/CRtool.php
    http://sim.okawa-denshi.jp/en/PWMtool.php

    and determined that in the 9V (12V actual) line a 330ohm (actual 325ohm) and 22uF capacitor,
    the output should fluctuate between ~4,5-7V.

    I assumed this should keep the led on constantly, but still the relay is opened and closed @ 143Hz.
    I tried 1kohm and 2.2kohm but the relay does not open at all.

    Any advice is welcome :)
    In the mean time, I'll try to set up my raspberry pi to get a 143Hz source..
     
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