ryanleung Posted February 28, 2006 Report Share Posted February 28, 2006 I want to use the IR diode to transmit the modulation signal to the receiver. I constructed this circuit and connect two IR Diode on the output(Vmod). I tested the IR diode using CRO, there has the modulation signal. But the receiver can not receive the signal. Is this circuit has any problem? thx.....carrier freq.:40kHzAudio: 4kHz Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 28, 2006 Report Share Posted February 28, 2006 Hi Ryan,Do you want to amplitude-modulate the carrier? Your circuit doesn't modulate, it just mixes the signals together.Also, your 4kHz modulation frequency is reduced by the attenuator of R2, C3 and the very low impedance of the transistor's emitter. Quote Link to comment Share on other sites More sharing options...
ryanleung Posted February 28, 2006 Author Report Share Posted February 28, 2006 the output is like this figure, can i transmit this signal to the receiver? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 28, 2006 Report Share Posted February 28, 2006 Hi Ryan,Your signal looks like AM modulation but I think it would have just the two frequencies mixed together instead of modulation and would look like this.AM modulators I have seen change the supply voltage of the carrier oscillator like this one. Quote Link to comment Share on other sites More sharing options...
ryanleung Posted February 28, 2006 Author Report Share Posted February 28, 2006 but this signal can transmit to the receiver using infrared??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 2, 2006 Report Share Posted March 2, 2006 IR can be directly modulated with AM or FM audio. Frequently high frequency subcarriers like 100kHz and 200kHz are used then FM modulated for stereo. Quote Link to comment Share on other sites More sharing options...
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