Questions about this symbol and set-up

Discussion in 'General Electronics Chat' started by freemindbmx, Mar 13, 2014.

  1. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    In the schematic I just wanted to make sure I got this right. For VCC and VCC/2. I know VCC means the power supply(voltage common collector) but for VCC/2, this just stands for the power being split, correct. And couldn't I just have the two 10uf capacitors that are in series together with the circuit be right after the voltage divder(the two 10k ohm resistors in series) instead of being after the TLC222. And then from there have a designated line on my perfboard that is connected to VCC/2,strictly used for components that need VCC/2.

    Also, the Box's labeled VCC and VCC/2, why have these? Instead of the Letters VCC and VCC/2?
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    You can have a dedicated line for the Vcc/2 as per the original circuit.

    The two 10uF caps must be after the OPA [TLC2272] that is being used as the power splitter.

    E
     
    Last edited: Mar 13, 2014
  3. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    so I would have one end of a 10uf capacitor hooked up to the power supply(VCC) while the other end is hooked up to the 1 pin of the TLC, and then have my other 10uf capacitor- one end hooked up to the 1 pin of my TLC and the other end to ground. right... and then I can designate a line on my perfboard that has one end hooked up to the 1 pin and the other on the designated line.
     
  4. ericgibbs

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    Jan 29, 2010
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    hi,
    Pin 1 of the TLC2272 is the Vcc/2 low impedance source, its decoupled by the 10uF to the +Vcc and 0V power rails.

    Refer to my modified drawing in my last post.

    If you used the the 10K resistor junction as the Vcc/2 it would be a high impedance source which would give you problems.

    Your description in your last post sounds OK.

    Do you follow OK.?
    E
     
  5. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    yes,just looked at it, I thought pin 7 of our AD was supposed to be VCC not VCC/2,ill go make a picture of explaning how id hook it up..just to make sure
     
  6. ericgibbs

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    Jan 29, 2010
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    Pin 7 of the AD must go to Vcc, not Vcc/2 , I made an error on my drawing.!!:eek:

    I will correct and repost.
     
  7. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    have it setp up like this,uploaded my picture below
     
  8. ericgibbs

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    Jan 29, 2010
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    Your sketch looks OK.
    E
    Sorry about the earlier Vcc mixup.
     
  9. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    no its all good, I added a VCC designated line as well.Just trying to make sure this is correct
     
  10. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    Are you laying out a PCB for etching or are you using PCB strip board.?

    A point to note on your circuit, even though the negative terminal of the 9V battery is connected to Gnd, the Gnd is actually 0V.

    So when you measure voltages on your circuit using DVM, you would use the 0V rail as the reference rail.
    The Vcc would measure +9V and the Vcc/2 would measure +4.5V.

    Also note the Gnd symbol on the RCA plug is not the same Gnd as the negative end of your battery.

    Why the designer has used the same Gnd 'label' for both types of Gnd is a confusing.

    The Gnd at the RCA plug should be named virtual ground which is Vcc/2

    If you dont follow that, just ask.;)
    E
     
  11. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    I have all the parts from left over projects. I kinda follow, im just using a reg perfboard with strips down the side. I'll have the battery hooked up at the top with + side hooked up to the left and - side hooked up to right. Thank you for pointing this out to me, if you could make a rough sketch of just the RCA or the hook-up with the battery on the perfboard,incase I got the hook-ups wrong.That'd be great,but if I have the idea of the battery hooked up right then let me know.

    But the RCA Ground is just hooked up to VCC/2 and would it be the same for our audio input that's hooked up to the 10uf and pin 3 of our LM, is this the Ground of the battery or our VCC/2,I believe this is our high pass filter
     
    Last edited: Mar 13, 2014
  12. ericgibbs

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    Jan 29, 2010
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    Hi,
    I have marked the +Vcc track in BLUE, the Vcc/2[Virtual Gnd] track in RED and the Common Gnd track in GREEN.

    Dont connect the RED to the GREEN track.

    E
     
  13. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    omg, you are amazing.....I'll go build it and get back to you later today :) I know I have to have something attached to the RCA Electrodes or the EMG becomes unstable,time to go find a cockroache and remove a leg
     
  14. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    It works like a charm, thank you.But I was looking up a EEG schematic that I could build,the schematic is made by the same people it seems, so all the Common Grounds are the same,and all the RCA grounds are the Virtual Grounds.You don't have to color code it if you don't want to.I would just like conformation that its the same idea as the other with its Common Grounds and Virtual Grounds.
     
    • EEG.pdf
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  15. ericgibbs

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    Jan 29, 2010
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    hi,
    Ref the last circuit there are a number of points I dont like about it.

    1. Connecting two batteries in parallel.
    2. Using a high impedance Vcc/2 source for the Vref pin #5 of the AD623.
    3. The same Vcc/2 also being used as an offset for U2B.
    4. As the audio amp is also on the same +Vcc rail I would add improved capacitive decoupling.

    Have you details of how the left side RCA sockets are connected to the external subject. [ Human/Animal Signal source]

    E.
     
  16. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    Two are connected to a muscle and one is referenced anywhere on the body with metal,like a braclet. Instead of two batteries in parallel how about just one 9v to power it. Also what would you recommend for an improved capacitance decoupling. I only learnded about decoupling recently.
     
  17. ericgibbs

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    Jan 29, 2010
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    hi,
    Add a 47uF and a 100nF cap in parallel, from +Vcc to 0V.

    E
     
  18. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    thanks, But wouldn't the 3 pin be the virtual ground if in not mistaken for the TLC
     
  19. ericgibbs

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    Jan 29, 2010
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    Hi,
    The feedback path for U2A is via the human body and R14, this sets the gain for U2A, so I dont see why pin #3 should be at virtual ground.

    I will look further, if there is a change I will let you know.
     
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