Cir ii

Discussion in 'The Projects Forum' started by kja00, Oct 26, 2009.

  1. kja00

    Thread Starter New Member

    Oct 14, 2009
    10
    0
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    I would say signal ground. You are referencing the input/output of the receiver/transmitter to it. Those are your signals...

    Protective grounds are usually for fault currents and chassis type connections.
     
  3. kja00

    Thread Starter New Member

    Oct 14, 2009
    10
    0
    Could it also be possible that GND is referring to GND on the 9V power source, i was just making the assumption that it was connected to the DB25 but maybe i'm wrong?
     
  4. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    It probably is referring to the GND of the 9V source. However, since you use signals off of other pins of the DB25 as input to your circuit I would think that you would also need to be referenced to the same ground as those signals as well.
     
  5. kja00

    Thread Starter New Member

    Oct 14, 2009
    10
    0
    I have tried building the circuit now, but it does not seems to work.

    Do you think that i should try to connect Signal ground of DB25 to the same rail where ground from my 9V source is connected?
     
  6. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    I think that you should connect it. Also, triple-check all your connections to make sure their wired correctly.
     
  7. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    I agree with both statements above...
     
  8. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    The reason I think you should connect both grounds is partly because of my amateur radio hobby. When we have all our radio equipment and everything it is important to wire all the grounds together to ensure an effective ground source. In addition, two different grounds for a complete circuit seems gratuitous and unseemly.
     
  9. kja00

    Thread Starter New Member

    Oct 14, 2009
    10
    0
    Now i am able to get the circuit to record the signals, but i cannot transmit. If i look at the two IR LEDS, Kingbright L-7113F3BT http://www.kingbright.com/manager/upload/pdf/L-7113F3BT(Ver1189403072.10) through a digital camera when i press the transmit button in the computer application, they are totally dark, if i look at the diode in the remote control when i press a button, i can see it light up, I have triple checked the circuit, and made sure that the orientation of the leds, transistors etc. is correct.

    Any suggestions on what the next thing i could do, to make this work?

    By the way i have noticed that when i record a button, there is two versions of the signal, first time the file have a size of 202984 bytes and second time 203200 if i compare the timings the are quite different, but there is only these two varaitions of the signal, fourth time the filesize is 202984 and the timings is identical to the first time the button was recorded. Is this correct?
     
  10. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    The photodiodes may have gotten damaged by not limiting the current through them when applying the +9V. The drop on the diode is 1.2V (typically) and the maximum current through the diodes is 50 mA. If you add a resistor to the path you can limit the current within the allowable range. You may have to replace the part now as it may already be damaged.

    If you have a voltmeter with a diode check, test both diodes as only one may be totally destroyed.

    To determine a starting point for you resistor, use V = i * R.
    V = 9volts - 2*1.2volts : battery voltage minus 2 diode drops
    i = 20 mA : matches graph for 1.2V drop
    therefore
    R = 330 ohms
    Find close resistor value.
    This does not take into account the voltage drop on the transistor or the exact voltage drop on each diode so you have a little room to play if you need to increase the power of the transmit side.
     
  11. kja00

    Thread Starter New Member

    Oct 14, 2009
    10
    0
    I really appreciate all your help.

    I have now tried to solder 330 ohm [100 ohm + 220 ohm in series] in front of the diodes and at the same time replaced both diodes with new ones of the same type as before, but it still seems like the diodes do not transmit anything because they do not light up when i look at the them through a digital camera, at the same time as sending the transmit command from the computer.

    Just to be sure that i have not misunderstood something. The two diodes that i have used is "infrared emitting diodes" of the exact same type. Somewhere on the website the author writes:

    Here he is talking about a signal diode, but the schematic show two IR LEDS so i guess that i am doing the right thing?

    I found out that i have some LTE-5208AC http://elektronik-lavpris.dk/files/sup2/E5208AC[1].pdf in stock should i try to mount these instead?
     
  12. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Without knowing more about what is on the website, he is probably saying that X1, the 3904 type transistor, could be any NPN transistor. I do not see any small signal diodes so I have to assume that there are either more circuits on the page you took it from or that he cut and pasted the comment from another place.

    I do not think there is any suggestion of using a standard NPN or small signal diode in place of the phototransistor and photodiodes.

    What type of signal are you sending to the DB25-2? Is it too fast for your camera? Try sending a slow signal... just on and off. Verify that the signal is getting to the drive transistor and that it in fact is turning on. Verify that there is a voltage drop across the photodiodes when the transistor is on.
     
    Last edited: Nov 1, 2009
  13. kja00

    Thread Starter New Member

    Oct 14, 2009
    10
    0
    The signal i am sending to the DB25-2 is a on/off signal that should replicate the recorded signal that is recorded by the phototransistor on the circuit.

    I will try to adjust the timing of the signal sent and check voltage drop.
     
  14. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,158
    kja... What signal levels are you using on the DB-25 serial port? RS232 standard can is unloaded is +/- 24 V.

    Before you can begin, you need to know what is a high and what is a low, per the specifications that you are using.
     
Loading...