SM2GXN Posted April 10, 2006 Report Share Posted April 10, 2006 By the way audioguru, have ever tried to simulate an AM circuit in switchercad? Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 10, 2006 Author Report Share Posted April 10, 2006 I think the base of the oscillator should be modulated then it can connect to a common-emitter LED driver transistor.An oscilloscope will show you what the transmitter is doing.sorry, I don't know your mean. can you draw a circuit to me, thanks!!! Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 10, 2006 Report Share Posted April 10, 2006 This AM modulated IR transmitter circuit should work: Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 10, 2006 Report Share Posted April 10, 2006 By the way audioguru, have ever tried to simulate an AM circuit in switchercad?No, ever since I heard how wonderful FM broadcasts sound, I gave up with the narrow-band, distorted and full-of-interference sound of AM broadcasts. Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 17, 2006 Author Report Share Posted April 17, 2006 hello audioguru.My AM transmitter output signal is 9.2Vp-p. And I changed the R1, R2, C and R3 to 2.7kohm, 10kohm, 0.01uF and 1Mohm. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 17, 2006 Report Share Posted April 17, 2006 Hi Ryan,Your opamp doesn't have its pin 4 connected! It also doesn't have a supply bypass capacitor.Your circuit doesn't have much gain:1) The collector load resistor for the phototransistor's value is much too low.2) The inverting opamp's input impedance of 10k is loading-down the phototransistor.3) The output resistance of the phototransistor is reducing the gain of the inverting opamp.4) An opamp type isn't spec'd that operates well at 38kHz.If your transmitter works, the range is reasonable and the phototransistor isn't picking up stray light or IR then my modified circuit should work well. Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 18, 2006 Author Report Share Posted April 18, 2006 Hello audioguru,I constructed your transmitter and the receiver circuits already. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 18, 2006 Report Share Posted April 18, 2006 Your IR receiver probably has a strong output at 38kHz now but you can't hear a frequency so high. Therefore the receiver needs to feed an AM detector diode and filter to recover the modulation. The transmitter circuit has two very important resistors that need adjustment. See my sketch.You are using Amplitude Modulation. Noise is fluctuations in amplitude that the circuit is designed to receive. You should be using FM instead, for low noise. Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 18, 2006 Author Report Share Posted April 18, 2006 Your IR receiver probably has a strong output at 38kHz now but you can't hear a frequency so high. Therefore the receiver needs to feed an AM detector diode and filter to recover the modulation. The transmitter circuit has two very important resistors that need adjustment. See my sketch.You are using Amplitude Modulation. Noise is fluctuations in amplitude that the circuit is designed to receive. You should be using FM instead, for low noise.two resistors?the AM detector means the envelope detector? Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 18, 2006 Report Share Posted April 18, 2006 two resistors?Sorry, I forgot to attach my sketch. The resistors are boxed in red.the AM detector means the envelope detector?Yes. Your receiver circuit needs one. Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 19, 2006 Author Report Share Posted April 19, 2006 should I amplify the signal again?(tansmitter and receiver) Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 19, 2006 Report Share Posted April 19, 2006 should I amplify the signal again?(tansmitter and receiver)The two resistors that I boxed with red in my receiver circuit reduces the gain. They should be adjusted so that the circuit doesn't overload with too much signal.Did you make an AM detector (envelope detector) to demodulate your AM modulation?What range are you trying? Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 19, 2006 Author Report Share Posted April 19, 2006 The resistor is 40ohm and the capacitor is 0.1uF. The frequency is 38kHz.Is it right?f=1/(2*pi*R*C) Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 19, 2006 Report Share Posted April 19, 2006 The resistor is 40ohm and the capacitor is 0.1uF. The frequency is 38kHz.Is it right?f=1/(2*pi*R*C)Yes, the capacitive reactance of a 0,1uF capacitor is about 40 ohms at 38kHz, but which resistor and which capacitor? Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 19, 2006 Author Report Share Posted April 19, 2006 hello audioguru~~I have are few question about my project.1. I constructed your receiver already. And I amplified the signal using opamp, then it was connected to the audio amplifier. But the sound is very weak. I try to adjust the volume but the sound is also weak. I don't know how to increase the signal. And the maximum distance only have about 5cm that is very short.2. I constructed the envelope detector (R=40ohm, C=0.1uf) and connected to your receiver output but the envelope detector output have not output signal.thanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 19, 2006 Report Share Posted April 19, 2006 I constructed the envelope detector (R=40ohm, C=0.1uf) and connected to your receiver output but the envelope detector output have not output signal.No Ryan.A resistor and capacitor is not an AM envelope detector. Also, a 40 ohm resistor and a 0.1uF capacitor is like a dead short at 38kHz to the output of an opamp. The minimum load for most opamps is 2k ohms.An AM envelope detector is a diode followed by a filter capacitor. Look at the circuit of any AM radio to see. Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 19, 2006 Author Report Share Posted April 19, 2006 how about the distance, the signal is very weak Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 19, 2006 Report Share Posted April 19, 2006 how about the distance, the signal is very weakDid you try it with the AM envelope detector circuit I sketched?I think you need to use an oscilloscope to see if the transmitter and receiver parts are adjusted properly for full modulation. Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 19, 2006 Author Report Share Posted April 19, 2006 Ok, I will try it.thanks Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 20, 2006 Author Report Share Posted April 20, 2006 The red circle voltage measured is not 5.9V, it is 9V same as the VCCIs it no current though the IR LEDs? Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 20, 2006 Report Share Posted April 20, 2006 The red circle voltage measured is not 5.9V, it is 9V same as the VCCIs it no current though the IR LEDs?Correct. Then the voltages for Q2 must also be wrong.I notice now that the voltage divider of R4 and R5 has its values too high for 1.9V on the base of Q2, when Q2 has 31mA of current in the LEDs. R4 should be 5.6k and R5 should be 1.5k. The resistor that I added in series with the base of Q2 must have its value reduced also.But then the total resistance might be too low for Q1 to drive. Try it.How do you know if Q1 is oscillating and what frequency it oscillates at? Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 25, 2006 Author Report Share Posted April 25, 2006 The circuit can sucessfully received the signal. If I want to add the Automatic Gain Control(AGC) to the receiver, how can I do???? Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 25, 2006 Report Share Posted April 25, 2006 The circuit can sucessfully received the signal. Quote Link to comment Share on other sites More sharing options...
ryanleung Posted April 27, 2006 Author Report Share Posted April 27, 2006 How can i increase the transmit distance?now, it can work 6-8 inch only Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 27, 2006 Report Share Posted April 27, 2006 How can i increase the transmit distance?now, it can work 6-8 inch onlyMaybe the phototransistor is being saturated by visible light. Is the range better when it is dark? Quote Link to comment Share on other sites More sharing options...
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