help identifying part please

Discussion in 'The Projects Forum' started by markosillypig, Apr 28, 2009.

  1. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    hi all
    i have just recieved my rc lighting module today
    i want to make another of my own but the problem is i do not know what this part is
    it has 2 markings on it 33 and m but i have no idea what it is
    on the photo attached it has 3 wires vcc + 4,8 volt vcc- and a signal that makes the curcuit come to life

    thanks if you can help
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Without more information, I'll have to guess that it's a voltage regulator.

    78M05 or something similar. The IC on the board was made by Microchip, which suggests a microcontroller. Most of Microchip's line will run on somewhere between 2.5v and 5.5v; 5v being preferred. That's how I came up with the 78M05. Oh, the 78M05 is offerred in that case style; other versions are not.
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Can you show the other side of the board? How are the three pins on the mystery device connected to the servo leads, if in fact they are connected. Are the leads from a receiver? What or where is the output of the circuit?

    The pins on the SOT-223 are numbered 1,2,3 from left to right, as shown in the photo. Is pin3 connected to the orange wire or does the orange lead simply pass under the perf board to the other chip?

    John
     
  4. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    pin 1 is connected to the brown wire pin 2 is to the red and pin 3 is to the orange the output from the receiver is 4.8 volts
     
  5. jpanhalt

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    Jan 18, 2008
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    Based on that, it is almost certainly not a voltage regulator.

    Can you post a picture of the underside of the board? Where is the board's output located and to what does it go?

    John
     
  6. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    hi the supply powers a pic 16f chip the signal then operates the pic to
    switch on or off a series of leds via the r/c transmitter
    photo attached

    see http://www.youtube.com/watch?v=gy65AXQEPbE
    this is what it does
     
    Last edited: Apr 29, 2009
  7. jpanhalt

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    Jan 18, 2008
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    That picture makes it look like the signal from the RX is NOT attached to the unknown device's pin3. The blue wire from the signal seems to go directly to the large chip (MCU?). Based on that, the unknown chip may be a voltage regulator as SgtWookie suggested.

    John
     
  8. tkng211

    Well-Known Member

    Jan 4, 2008
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    You can measure the voltage at each pin of the IC and tell us here. I believe it's a 3.3V LDO voltage regulator because the incoming vcc+ is just 4.8V and there are two tantalum capacitors in the circuit. You can take a look on the following web page
    http://www.national.com/ds/LM/LM1117.pdf
     
  9. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    i think you could be right a very close inspection has reviealed that the 3 points on the smd have had 3 wires soldered on the them which threw me off in the first place
     
  10. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    can any one tell me what purpose the ldo has on the circuit ans the input voltage is 4.8 v and the ldo is 5 v
    thanks
     
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I'd bet for sure its a 3pin voltage regulator with a tantalum cap on the input and output, and the other pin is Gnd. You can see the ground pin and +Vcc pin on the bottom of board by tracing back from the 2 PIC power pins. Whoever labeled the pins got it wrong. :)

    It's probably a 5v unit to protect the PIC if the user connects a 6v supply like a 4 battery pack etc. Or it might be a 3.3v etc to be used with a lower supply. One poke with a voltmeter should tell you.
     
  12. tkng211

    Well-Known Member

    Jan 4, 2008
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    The input voltage is 4.8V and the output voltage of the LDO ( Low Drop Out ) regulator is 3.3V. There's a dropout voltage across the regulator of 1.5V (4.8-3.3).
    If the common voltage regulator IC like 7805 or LM317 is used, we should allow a minimum dropout voltage (between the input and the output of the IC) of 3V to have a proper regulation because the internal control device is a bipolar transistor. When a transistor works in the amplification zone, the voltage across the collector and the emittor should be bigger than 2V. We won't get the 7805 regulator worked properly if the input voltage is below 8V. Hope you can understand my explanation.
    BTW, you can measure the output voltage of the LDO regulator to see if it is 3.3V.
     
  13. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    right for the last question boys
    do i need the ldo on the circuit if the input is 4.8 v and the ldo is a
    5 volts ???
    thats all folks
    thanks
    marko
     
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Yes. 4.8v in "remote control" terms means 4x 1.2v NiCd. This may be fast charged on most RC type fast chargers which can hit the batteries with as much as 1.5v per cell, which is 6v total.

    Using a 5v LDO on a 4.8v rechargable battery pack is pretty common and makes sense.
     
  15. jpanhalt

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    Jan 18, 2008
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    I have not really seen that practice. NiCd and NiMH in my experience charge to about 5.35 to 5.55V for a 4-cell pack. That is not enough to run a 5V LDO, at least not the ones I have. Presumably, the batteries are isolated from the circuit during charge.

    John
     
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