Just tie the collector to + and put your 300R and LED in the emitter to ground.
Rick

Robert Rothe wrote:

> 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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