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A bit of help with a diagram

Discussion in 'General Electronics Discussion' started by SFC, Apr 30, 2015.

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  1. SFC

    SFC

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    Apr 30, 2015
    Diagram.JPG

    Hi all,

    Please bear with this electronics noob (yes, I'm an ICT nerd and part time wannabe scientist ;)), but I have a few questions about a diagram before I start heating up my soldering iron and wreck this thing.

    I bought a cheap and simple video TX/RX combo for a WiFi remote controlled Arduino tank project. With the RX module came a wiring diagram. I am capable of googling for the basics, but putting it all into perspective is another thing.
    Since the image was fuzzy and the description in chinglish, I had to squint, tilt my head slightly to the right and make my pupils oscillate by imitating a buzzsaw with my lips to be able to read it. :p

    Looking at the diagram I made out I will need (and please correct my mistakes with due scorn); 1x 220 µF 10V polarized radial electrolytic capacitor (227/10V) ,2x 1µF non polarized capacitors (105), a 3 way dip switch, 2x 470 µF 16V polarized radial electrolytic capacitors (477/16V), 2x 0.01µF non polarized capacitors (103), 1x 1N4148 diode, 1x LM7905 voltage regulator, a bunch of (female) RCA connectors, a DC jack, and some appropriate colored wires.

    Now, for the part I put in a red square a few questions arise:
    Since this is a RX unit, it receives signals and the RCA jacks should have been marked V-out, AL-out and AR-out. Correct?
    This made me wonder if the polarized capacitor in the diagram is drawn the correct way around. Since the video jack has a (common?) ground and the + sign on the capacitor is on the opposite side of the RCA ground, I assume it is correct?
    Also, am I correct in assuming the capacitors are used to filter the signal, making it 'cleaner'?

    Then the part in the orange square has me a bit more puzzled;
    I understand the current comes in from the DC jack, flows in the direction of the diode, voltage getting regulated (cleaned?) by the LM7905 and providing power to the RX module via the VCC (Voltage Controlled Clock?) pin.
    But what is the P_EN pin? And why is the +5V connected to the last 103 capacitor (green circle)?

    And last of all, how do I connect the (common?) ground? Should I connect all ground points to a conducting (metal) casing and the DC jack ground to this casing, or should I connect all the ground points directly to the ground pin of the DC jack?

    I'm sorry for the deluge of questions, but I would greatly appreciate if they were answered to help me understand this which is unfamiliar territory to me.


    Kind regards.
     
  2. davenn

    davenn Moderator

    13,903
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    Sep 5, 2009

    1) you are not going to pass a video signal through a 220uF cap and still have it useable

    2) up the audio input caps to around 1uF

    3) the input to the regulator ... what is the voltage ? if around 12V you will need a 470uF 25V cap

    4) you don't need a 470uf on the regulator output ... 100 uF maximum would be plenty

    5) the 1N4148 in the input to the regulator would last a few seconds maybe ..... replace it with a 1N4007




    you have just said, that those sockets RECEIVE signals so they should be marked INPUTS

    as I said earlier ... 220uF in there is way too high drop it to somewhere around 0.001uF ( experiment


    that's just showing you that there is +5V at that point ( from the regulator ) and may be useable elsewhere


    where did this circuit come from ??


    Dave
     
  3. SFC

    SFC

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    Apr 30, 2015
    Ok, so this cap should be lower? What will happen to the signal if 220µF is used?

    I found that a 105 cap is 1µF, non polarized type.

    It should be between 9V and 5V according to the spec sheet.

    Please explain this part a bit more, like I said, I'm a noob when it comes to electronics.



    Well yes, the RX receives signals from the TX, but the RCA jacks (output) send it to the displaying device, or do I have it backwards?

    Would love to experiment, but don't want to blow up the RX unit :)


    Ok, so if I would have 6V input at the DC jack, it should be 5V after it passed the regulator?

    From an obscure Hong Kong office building by the guy selling this at a price I would not even get up for in the morning. But I'm guessing it shows.. :rolleyes:
     
  4. davenn

    davenn Moderator

    13,903
    1,971
    Sep 5, 2009
    a video signal is really high freq ... it will be severely filtered and distorted

    doesn't matter if it's polarised or not use a 1uF polarised

    the reg will need a minimum of 8 - 9V input to get a stable 5V output

    a 1n4148 shouldn't be used there because it doesn't have the current capability a 1N4007 have a 1A rating


    you are contradicting yourself .... look at the diagram it clearly says Vin, AL in, AR in
    so they should be labelled inputs

    that wont happen .... no playing with this component anyway

    NO see my earlier comment ... you need at least 8V - 9V input to get a stable 5V output


    Dave
     
  5. SFC

    SFC

    8
    0
    Apr 30, 2015
    Well, that's just the issue Dave, it is a video RX, a receiver, it receives signals from the TX, not the RCA jacks. The RCA jacks are to output the signals to a displaying device (LCD/TFT/IPS). Hence my first question about the faulty labeled RCA jacks (or so my logic assumes). The RCA jacks are output, the DC jack is input to power the RX. The data sheet shows 9V max input, and uses mA's nowhere near a full A. 105 caps are 1µF, so they should be the correct type to use if I'm not mistaken.
     
    Last edited: May 1, 2015
  6. davenn

    davenn Moderator

    13,903
    1,971
    Sep 5, 2009

    ohhh ok ... that clarifies it :) then the diagram is incorrectly marked and you should be labelling them outputs :)

    no probs ...but I still would never dream of using a 1N4148 for that purpose, use a 1N4007
     
  7. SFC

    SFC

    8
    0
    Apr 30, 2015
    I am not a complete nitwit when it comes to electronics and diagrams, but that's why I'm asking the pros here ;). I kinda thought the diagram looked iffy here and there.

    Ok, so replace the 1N4148 diode with a 1N4007, check.. But I would like a bit more explanation, my goal is to learn about electronics while I tinker with it.

    1. The 1N4148 is a switching diode, so it's fast, the 1N4007 is a rectifier and thus slower, correct?
    2. Even the highest rated 1N4148 I could find was rated for 450 mA peak, so that's why you think it won't last in this circuit, right?
    3. Both would act as a flyback diode in this circuit to eliminate the voltage spike occurring when the power supply is removed or switched off, true?

    In the light of the video signal being an output instead of an input, would I still have to change the 220 µF 10V capacitor to something else? And if so, to what?

    Could you perhaps 'improve' the diagram to make it visual for me, I think it would help me understand :).
     
  8. davenn

    davenn Moderator

    13,903
    1,971
    Sep 5, 2009
    I always like to make sure that components carrying any reasonable current are a bit overrated for the job
    less likely for them to fail

    No, the diode is there for reverse polarity protection.... in case the DC input had its ± reversed

    a 220uF cap is going to corrupt a video signal regardless of the direction through it
    again, you could experiment, but I would suspect something in the 100pF to 1000pF (101 - 102)

    I have done lots with video transmitters and receivers for my amateur radio work
    I will dig out a receiver later and see what values were used in those circuits :)



    Dave
     
    Arouse1973 likes this.
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