Debugging an openSource drawdio circuit (TLC555 Based project)

Discussion in 'The Projects Forum' started by Ilisparrow, Oct 3, 2016.

  1. Ilisparrow

    Thread Starter New Member

    Feb 22, 2016
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    Hi,
    I'm a student in EE, I wanted to make my own design, of the drawdio project.
    The makezine project page is here : http://makezine.com/projects/drawdio-musical-pencil/
    The project is a signal generator, wich then will be amplified and then send through a speaker, as the frequence changes in fonction of the resistance, by changing it you can generate differents sounds.
    I need your help, please, because i made an eagle design, then made a pcb from it, but it doesn't work and I absolutly don't know How and what can i do to make it work or to debug it ! I'm stuck at the point of not even knowing what could possibly can be wrong.

    Every thing is open source, open hardware :
    Here are images of the circuit :
    https://www.dropbox.com/s/vq0eujimaztvjfq/Capture d'écran 2016-10-03 10.48.59.png?dl=0
    Here is a PCB :
    https://www.dropbox.com/s/6acar1xhvjh5heb/Capture d'écran 2016-10-03 10.57.37.png?dl=0

    And here is a link to the files (You can do whatever you want with them) :
    https://drive.google.com/drive/folders/0B_3KYG32FUbvNk9VamlLbjQxN2c?usp=sharing


    Thanks in advance for your help.
    Ilias.
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Your circuit shows two different chip numbers for the '555. Check the supply voltage requirements for the particular '555 that you are using. For instance the NE555 minimum supply is 4.5V, the TLC555C will work down to 2V.
     
  3. Ilisparrow

    Thread Starter New Member

    Feb 22, 2016
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  4. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    There is a lot wrong with this circuit. The transistor is doing nothing useful, and the PCB does not match the circuit diagram.
    Are you up to cutting tracks on the PCB and adding link wires on it?
     
  5. Ilisparrow

    Thread Starter New Member

    Feb 22, 2016
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    I don't understand, why is the transistor doing anything ? On the original circuit, it's exactely the same transistor, and the same configuration !
    And for the PCB, I made them with eagle and autorouting, there are no design errors.
    I can, add wire to make it work then, correct the PCB design.
    And thanks again.
     
  6. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    The speaker can be connected via the 100uF capacitor directly to pin 3 of the '555 and the transistor and 10Ω resistor can be removed.
    Looking at the PCB layout it connects pin 2 and pin 3 of the '555. This is not correct.
     
  7. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,889
    375
    I just looked at the 'musical pencil' page and I think I can see how this happened. On their circuit diagram the wires from pins 2 and 3 cross but are not connected - there is no connection dot. The PCB you show is as if there was a connection there. See the red box below. drawdio_schem_pinout.jpg
     
  8. Ilisparrow

    Thread Starter New Member

    Feb 22, 2016
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    Ok, thanks. I see it now. I will correct it on the PCB layout, and for my prototype i'll drill a hole through the PCB.
    I'll keep you updated, if you want.
    And for the transistor, do you think that it's better to make the current go thourgh the transistor or it will not affect the life cycle of the TLC 555 ?
     
  9. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,889
    375
    The transistor won't make it any louder and there is no resistor to limit the base current. If you keep the transistor add a resistor between the base and pin3, about 1kΩ should work OK.
     
  10. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,889
    375
    If you mean drill a hole between pins 2 and 3 that won't fix it all. Pin 2 should be connected to pin 7 and to R2, C2, but not connected to the base of the transistor (which it is at the moment).
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    That would work better with an NPN emitter follower - as it is, the B/E shunts the output and relies entirely on the CMOS inherently current limiting.
     
  12. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,889
    375
    The TLC555 can supply 100mA so to get any benefit the transistor would have to be able to handle more than that. That would be unlikely with the standard 9V block battery which TS is using now.
     
  13. Ilisparrow

    Thread Starter New Member

    Feb 22, 2016
    11
    0
    Hi,
    Thanks,
    I tried to correct them by tinkering, but i couldn't make it.
    I corrected the mistakes on the files.
    Here are links to the circuit and pcb pictures :
    https://www.dropbox.com/s/8rm27tpb9k4zg2f/Capture d'écran 2016-10-04 16.57.34.png?dl=0

    https://www.dropbox.com/s/bn68ie69nbko9un/Capture d'écran 2016-10-04 16.57.46.png?dl=0

    And here is a link for the files :

    https://drive.google.com/open?id=0B_3KYG32FUbvSklMUkZmaXdOcE0

    I can't remove the transistor, because I also made pedagogical booklets that explains how it works (They are open source, and i can post them if you are intersted, but they are in French).

    Do you think, they are good enough to order them ?
    Have a nice day.
     
  14. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,889
    375
    You need a resistor (1k) between pin 3 and the base of the transistor. Without it, the transistor will probably have a very short life.
     
  15. Ilisparrow

    Thread Starter New Member

    Feb 22, 2016
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  16. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Your link to the circuit is actually another link to the PCB so I can't fully check it.
    There is still a possible problem as the TLC555 output may not go high enough to fully turn off the transistor.
     
  17. Ilisparrow

    Thread Starter New Member

    Feb 22, 2016
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  18. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    This circuit may work as it is but it may not. The simplest solution is to replace the 2N3906 with a 2N3904 and swap the emitter and collector.
    What supply voltage do you want to use?
     
  19. Ilisparrow

    Thread Starter New Member

    Feb 22, 2016
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    Why would a PNP transistor work better than an NPN one?
    And I made the circuit for 3 V but the LTC can easily handle 9 V.
    What would you suggest?

    That worked great on the make project.
     
    Last edited: Oct 5, 2016
  20. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    The output of the '555 goes down very close to ground but the high level output, from the datasheet, will be about 1.5V less than the supply. that is enough to keep the PNP turned on. If it doesn't turn off properly you will get little or no output.
    Using the NPN as an emitter follower, the '555 can bring the base down close to ground so it will definitely turn off. When the '555 output is high, 1.5V below supply, can take the NPN base up to 1.5V with a 3V supply. The emitter base voltage drop (about 0.6V) will reduce that to just 0.9V and that is your output voltage. If you use a higher supply voltage you will get more output. I don't know the particular speaker you have but if is too quiet at 3V you can make it louder with higher supply voltage.

    If you use the NPN don't forget to swap the emitter and collector connections.
     
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