Sound to light Help please

Discussion in 'The Projects Forum' started by Fenris, Jul 5, 2008.

  1. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    hi all

    I have a sound to light unit which is a converted vellaman kit. All i have done is remove the 4 LEDS and added a BD139 and a 2N3055 transistor to drive 2 12V 24W filament bulbs in parallel. Now i had problems initially with the bulbs coming on with no input and then reacting to an input. I was told to change 4 resistors to help overcome this. I want the lights to only come on with an input. I have just managed to test it again with the changes and the proper bulbs and they come on with no input and pulse to an input. without the bulbs plugged in the LED reacts as it should, only coming on to an input. Can someone please help me sort out what i need to do to get the correct reaction with the bulbs on. The circuit runs on a 12V DC battery.
    Incidently if the pot is turned to the lowest setting of sensitivity a buzzing is introduced across the voice modulator it is connected to, if i increase the vr setting the noise stops. in the picture it is R28, 31, 32, 33 that where changed. the figures in brackets are the original resistor values. thanks in advance. i am a novice and i am struggling to work out what i need to do to sort it out.

    a single 12v 2.2W bulb works fine if that gives any clue as to what needs tweaking

    Regards

    Dave
     
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  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What is the original velleman kit number?
    Is there an original schematic?

    Greetings,
    Bertus
     
  3. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    yes i have it here. the transistors that came with the kit in my instance where 548 and 558 also the 1M resistor in my schematic was a 1M5. thanks for looking. Although it counts for very little in the real worls i was able to run the circuit on my PC in a virtual circuit spice type program.

    regards

    Fenris
     
    Last edited: Jul 5, 2008
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I think the levelshifter is giving trouble.
    I have modified your schematic, perhaps you can give it a try and report back what happens.

    Greetings,
    Bertus
     
  5. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    thankyou very much. i will try the modification tomorrow and let you know. the circuit is on a homemade PCB so i can easily disconnect the relevant parts and wire the DB back to the new point with the changed resistors. incidently the LED i am using is a 12V with built in resistor.

    regards

    Fenris
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    896
    The circuit from Bertrus will keep the lights on most of the time.
    Your circuit will keep the light turned off most of the time.
    They light because the transistors have their pins connected backwards or because the transistors are blown.
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You can try to find a point where the light is (almost) off by lowering the 100K.
    The audio wil turn it on when it is loud enough.

    Greetings,
    Bertus
     
  8. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    ah yes. i have just done the changes and the lights are on with no input still, so, i need my setup so that the bulbs are off when the circuit is powered and only come on when i speak into the mike. which transistors are most likely be blown? the BC's , BD or the 2N. even though the LED without the bulbs present worked as expected would the transistors still be blown? thanks for your input.


    just caught that last post, will give it a try.
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    896
    That won't work because your value of R27 is way too low.
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    @ audioguru, what values do you sugest.
    I have used hfe of 40 for the BD and 20 for the 2N, so a gain of 800.
    For the 4 A of the bulbs you need 4 A / 800 = 5 mA basecurrent.
    12 V - 1.4 = 10.6 Volt across R27. 10.6 / 5 mA = 2120 Ohm => 2k2.

    Greetings,
    Bertus
     
  11. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    hi there

    well i just tried 3 different values down to 10K on the last and the bulbs persist in staying lite, no change in strength either. i would be grateful for any input to try and solve this problem. as i mentioned earlier i struggle at this level i lack a certain something that would probably allow greater understanding and my maths and application therein is abysmal so i am unable to piece together the info myself. VIR i can do but using it within a circuit is beyond my abilities which is a shame because i enjoy building circuits. Is my original circuit closer to the solution? is it just resistor values that need tweaking in it to get the 'trip' level right? my only other thought early on when i first thought of using the circuit to power filament bulbs was to use and opto-isolator as the trigger for a higher power transistor. Is that a viable option and how would i go about it? i know the opto would simply replace the leds, with a resistor in series, of the original circuit but how would i connect it up to the bulb control transistor?

    Regards

    Fenris
     
  12. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    further to my last post i found this. its a vellerman low voltage sound to light kit MK114. it can handle the wattage of bulbs and it can run on dc. but it needs a minimum input of 2W by direct connection to the speaker. now i could connect it to the speaker output of my voicemod, but, due to the way that works there is a low level buzz permanently at the speaker which although not to audible to the human ear may trigger the unit without vocal input but there is the variable resistor there to tweak it. or could i just splice it into the original vellerman sound to light circuit i showed earlier? here is a picture of my idea for joining the 2 together and a schematic of the MK114. i think splicing the 2 may be unneccesary but your thoughts would be appreciated on this turn of events.

    regards

    Fenris
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I found an other schematic for a light organ.
    The text is in finnish, but the drawing and pcb is clear.
    It has 3 channels low mid amd high frequencies are filtered

    Greetings,
    Bertus
     
  14. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    thanks for that m8. i have however to my irritation stumbled across a exactly what i need and it transpires that according to a collegue on another forum......his exact words were 'oh yes thats what i did' it is actuall another velleman kit! the MK114 heres a schematic. the only change i will make is taking the cluster of 6A6 diodes off as the circuit can go AC 12V or DC 12V i want it strictly DC. cheers for your input everyone.
     
  15. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have changed the schematic.

    Greetings,
    Bertus
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    896
    Hi Bertrus,
    1) hFE is used for a linear transistor that has plenty of voltage across it.
    A transistor that is used as a saturated switch needs to have a lot more base current than the hFE number.

    The minimum hFE for a 2N3055 is 20 when it has a collector current of 4A and a VCE of 4V or more. Its max saturation voltage (VCE) is 1.1V when it has a collector current of 4A but when its base current is 400mA.

    The minimum hFE for a BD139 is 25 when it has a collector current of 400mA and a VCE of 2V. Its max saturation voltage is 0.5V when its collector current is 500mA and its base current is 50mA.

    The combined minimum hFE of both transistors is 10 x 10= 100 when they are used as a saturated switch. So they need a base current of 40ma, not 5mA.

    But the problem with your circuit is that the output transistors are always turned on.
     
  17. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    @ audioguru,
    How to change the ciruit that the light is not on?
    Must we have another type of driver for it?
    I am willing to learn about it.
    I have not build something for a long time.
    I used to do a lot with TTL in the past, but this is linear.

    Greetings,
    Bertus
     
  18. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    hi all

    bertrus thats what i did. new PCB is made using glossy photo paper to transfer the design which turned out to be better than using press n peel which despite my best efforts had a tendency to warp the design at the edges causing poor definition of track spacing requiring tidying up with a sharp knife. thanks for your input gentlemen i am very grateful. heres a pic or 2 of the work in progress.

    regards

    Fenris
     
  19. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Gee Fenris, your PCBs are coming out quite nice with the glossy photo paper.

    What is the exact paper that you used?
    What is your printer make and model?
     
  20. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi there

    thanks very much. i was pleased as well especially as the photo paper performed better than supposedly dedicated paper. It was nothing fancy. mine was laser printer compatible glossy photo paper. matt will do as well. i got it printed on the local printers laser printer/photo copier machine. though it should be possible on any laser printer. Using a tutorial from youtube the iron was set as high as possible used to warm the PCB, applied the transfer put a piece of paper over that then ironed it. pressure was applied whilst sweeping the iron over the the board for about 3 minutes. it takes a while to soak the paper off afterwards which must be done layer by layer. that took about 30 mins but the result was excellent. The letter W in the word with of the top line of text on the board is 1.5mm tall so you can imagine how thick its 'limbs' are.

    regards

    Fenris
     
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