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LFO LED indicators

Discussion in 'Audio' started by darren adcock, May 31, 2018.

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  1. darren adcock

    darren adcock

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    Sep 26, 2016
    Wasn't sure if this should go in 'audio' or 'optoelctronics'

    I've been trying circuits out today to see if i can find one that will sweep the same as for example a Sine wave that's in the region of +/- 5v at it's control voltage out. I've found I've misunderstood something in that the LED only lights up when in the positive part of the oscillation. And stays off when in negative. Which when typing it out here seems obvious.

    So I tried to find a circuit which would convert the +/- waveform into a positive only version but didn't know the correct terminology or I'm going about this the wrong way... I expect both.

    If anyone can help that'd be great and stop me going round and round in circles, and breaking those pesky breadboard jump leads as i go :)

    I've attached the MFOS VCLFO schematic so you can see which circuit i'm using mfos schematic vclfo.gif

    Thanks in advance
     
  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Why bother. Use a red/green two-pin LED that will light on both cycles, red for positive, green for negative (or vice versa if you reverse it).
     
    davenn likes this.
  3. darren adcock

    darren adcock

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    Sep 26, 2016
    I would like to eventually use the indicators to be coupled with an LDR so I can control motors outside the synthesizer. In the past i've used the attached circuit with success, It's familiar to me. Would you go about this a different way? tip120 motor control.gif
     
  4. kellys_eye

    kellys_eye

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    Jun 25, 2010
    On the KISS basis there's nothing wrong with they way you show the motor drive - if you want to use 'ordinary' LEDs than any two connected back-to-back will work. Fit them into a tube with the LDR at one end.
     
  5. darren adcock

    darren adcock

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    Sep 26, 2016
    Cheers K.E, the circuit was from a member off here, whom i can't remember and can't seem to find the original post to credit them

    In terms of connecting the LED's back to back; would this mean that one is off when the other is on? I can't quite see how this would speed up and slow down a motor at the same rate as the waveform for when it drops into it's negative cycle?
     
  6. kellys_eye

    kellys_eye

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    Jun 25, 2010
    precisely.

    The motor will run at a speed determined by the light level falling on the LDR (as I'm sure you're aware) and one LED will light from '+' down to '0' and the other LED will light from '0' down to '-' (depending on the polarity of the output).

    What you won't get (not sure if you're looking for this though) is the motor changing direction as the voltage goes from + to -.
     
  7. darren adcock

    darren adcock

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    Sep 26, 2016
    Thanks for your help

    No need for motor direction change
     
  8. bigkim100

    bigkim100

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    Apr 17, 2013
  9. darren adcock

    darren adcock

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    Sep 26, 2016
    Hi, thanks.... harrrr, not needing to dazzle my eyes this much though, already too much to look at with snaking patch cables. I've had success today with following K.E's advice using two LED's. However I still don't get the motor to speed up and slow down for the full +/- 10v cv range. But then I don't quite know how to ask how to do this so maybe I'm just needing to learn a bit more with what I have for now. Or possibly an LED/LDR approach isn't quite suitable.

    I enjoyed the second video however, so added this quick edit, might be a fun addition/project when I've exhausted my module making needs :)
     
  10. bigkim100

    bigkim100

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    Apr 17, 2013
    Im not exactly certain why you are using the whole LDR thing, why can you not use a mosfet with a direct connection?
    Maybe the more skilled members of the group can answer that.
     
  11. bigkim100

    bigkim100

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    Apr 17, 2013

    Can he not directly connect something like a Mosfet to his output LED, driving the motor directly??
     
  12. darren adcock

    darren adcock

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    Sep 26, 2016
    I wasn't sure if this would effect the synthesizer at all, and seen as I've only just got it back working (after getting the power distribution wrong) I figured keeping the motor circuit and synth circuit separate was best for now, so went for LED LDR approach. I'm not complaining about the results I've had as I have had fun playing with it today, and is going in the direction I've been thinking about for a while.
     
  13. darren adcock

    darren adcock

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    Sep 26, 2016
    Also, I can just run the LFO seperately from the synth and try connecting it to the mosfet that way.
     
  14. darren adcock

    darren adcock

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    Sep 26, 2016
    Tried this today and worked fine, more detailed than the LED/LDR version. Needed to put a 2k resistor between CV out and base of the MOSFET is all as it seemed to flatten out the 0/- cycle somewhat. I'll make both versions so I can have the option of using motors which need more power without stealing from the synths needs. Thanks for your help.
     
  15. darren adcock

    darren adcock

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    Sep 26, 2016
    Here's the schematic I've ended up settling on, in case it needs correcting as I intend on making several over the next week or two into dual modules. There may be a more standard way of naming the two pots, which would be better on the synth panel. DSC_0565.JPG
     
  16. darren adcock

    darren adcock

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    Sep 26, 2016
    Got this module made today, plugged it in and noticed this behaviour happening when the motor is driven. I only had the circuit connected via the SQR out on the LFO and it effected the pitch on the VCLFO going straight into the mixer. Just wondering if anyone can help me understand what is happening please? so I can try and make the circuit better. The Oscilloscope is connected to the mixer output, initially the signal is shown without the motor connected, then it is connected and is turned on and off by the the SQR out on the LFO. Thanks in advance.

     
  17. darren adcock

    darren adcock

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    Sep 26, 2016
    Also, apologies as the title of this thread seems irrelevant now. I just didn't foresee having problems with the initial KISS solution. Maybe the title of the thread needs changing?
     
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