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current detector with led power on — Parallax Forums

current detector with led power on

FovakisFovakis Posts: 8
edited 2013-11-10 13:10 in Accessories
Hi to all !

I have this 3 pole filter in my receiver's last stage. I want to put a led, so when the current is passing through my circuit the led will light on. I need this because my transmitter a lot of time, don't work fine, so i don't know if there any signal going to my receiver.
It is a way to check it.

Any ideas for cheap consuption ?http://i1284.photobucket.com/albums/a578/fovos1/Circuit_zpsb91f9e29.png

Comments

  • kwinnkwinn Posts: 8,697
    edited 2013-11-04 20:27
    An op amp or single transistor circuit driving a led should be enough to indicate a received signal. Use the output of the filter to drive the op amp or transistor.

    What is the power supply voltage used in the circuit?
  • FovakisFovakis Posts: 8
    edited 2013-11-07 05:47
    Hi friend ! THE voltage supply is +15 Volt single supply.

    I am thinking to put the transistor for example at the output of the active filter. I DON'T want to loose huge amount of Voltage output from the transistor because at the voltage output is the signal that i must transfer. any idea of the topology of this transistor? BJT or FET ? Common emitter maybe? i am a beginner ! thanks a lot
  • kwinnkwinn Posts: 8,697
    edited 2013-11-09 13:16
    Try the circuit that is appended to the schematic you linked to in post 1. You may have to adjust the resistor values depending on the signal levels in your last stage. Make sure you use a high efficiency led for this. The 470K resistor (R3) determines the led brightness when there is no signal, and should barely light at that point. R2 (4.7K) limits the led current to about 3mA and determines the maximum brightness when there is a signal present.
    Led signal indicator.jpg
    944 x 554 - 141K
  • FovakisFovakis Posts: 8
    edited 2013-11-10 03:40
    kwinn wrote: »
    Try the circuit that is appended to the schematic you linked to in post 1. You may have to adjust the resistor values depending on the signal levels in your last stage. Make sure you use a high efficiency led for this. The 470K resistor (R3) determines the led brightness when there is no signal, and should barely light at that point. R2 (4.7K) limits the led current to about 3mA and determines the maximum brightness when there is a signal present.

    okk kwinn you are professional! tha's exactly what i wanted to do. Many thanks for that really! :smile:

    What is the max current that led circuit "keep","steal" from my output?

    Also, where in google i can search for that topology to understand why you put the devices in that order? it has any name?

    Many thanks for that !
  • kwinnkwinn Posts: 8,697
    edited 2013-11-10 13:10
    The transistor will draw a maximum of 0.7mA when the signal is 15V peak to peak. Less when the signal is lower. It should have very little effect on the signal.
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