I'm still learning, so please forgive my ignorance.  I have an IR detection module (an old radio shack one) that detects IR signaling at about 40 kHz.  It drives its data line LOW when a signal is received.  I have it hooked up to shut OFF an LED when a signal is present using this circuit:



                                      VCC 5Volt
                                       +
                                       |
              o-------------------------
              |                        |
              |                        |
              |                       .-.
              |                       | |300R
              |                       | |
              |                       '-'
              |                        |
              |                        |
              |                        |
              |                        V LED
              |                        -
              |                        |
              |                        |
            2 o                        |
                               ___   |/
       IR   1 o--------------o|___|--| NPN n2222
       Recvr                   1K    |>
                                       |
            3 o                        |
              |                        |
              |                        |
              |                       ===
             ===                      GND
             GND



I wanted to invert the process so that the LED lights when a signal is present so I tried this circuit:

                                      VCC 5Volt
                                       +
                                       |
              o-------------------------
              |                        |
              |                        |
              |                       .-.
              |                       | |300R
              |                       | |
              |                       '-'
              |                        |
              |                        |
              |                        |       LED
              |                        +------->|------+
              |                        |               |
              |                        |              ===
              |                        |              GND
            2 o                        |
                               ___   |/
       IR   1 o--------------o|___|--| NPN n2222
       Recvr                   1K    |>
                                       |
            3 o                        |
              |                        |
              |                        |
              |                       ===
             ===                      GND
             GND



This seemed to work OK except that I get some odd indications on the LED that IR is being detected.   I suspect they were there in circuit #1, but couldn't be seen.  (I grounded the metal can of the detector module.  Putting a sunglass lens over the module helped a bit, too)

Are these (especially the second) the right way to do this?

My second question is, if I decided to just use an inverter (ie, 7404), I'm unclear how to determine in the data sheet how much current it (the 7404) can sink.

Sorry for the simple questions.  Any help would be greatly appreciated.



Rob

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