Hi All,
Absolute beginner here, I need an advice on the following project:
I am trying to encode messages using ultrasound. I have wired three 555 circuits in astable mode as in this link (http://www.markallen.com/teaching/ucsd/147a/lectures/lecture4/7.php). Each of the IC's are producing a different high frequency sound centered around 20 khz. So it is not audible but also not too high freq (because down the line I want to be able to decode these by recording it in an ipod or iphone.
I then switch these according to the morse code using digitalWrite on 3 pins of an arduino circuit (i dont want to manually click the the code, but rather but it in arduino's memory and i want it to quickly cycle through this message (each pulse being around 30 to 50 miliseconds). I have the follwoing questions:
1) is this a clever way ?, i dont know if I can use a single 555 circuit and somehow change freqeuncy of this based on dots dashes and spaces (each represented by a unique frequency) rather than using three ic's. If this is possible it would maybe also help with the other problem below
2)There is this terrible clicking noise between pulses as I switch from one 555 to another (all output pins are wired to the same speaker). I tried to build a voltage ramp on supply voltage to the ic's using a diode and a capacitor, it helps a bit but not much (and believe me i tried every cap value from 1pf to 1000mf). I put a low pass rc filter to output, this reduces clicks but also attenuates a lot, so when i amplify again the clciks are back
Can you please help< i've read everything i could find. In the end i either want to create an envelope around the signal so it ramps up and down smoothly between frequency changes, or switch frequencies at exactly zero level voltage during the oscillation. I have tried to read everything I could understand, I am going nuts, please help.
Thanks
Absolute beginner here, I need an advice on the following project:
I am trying to encode messages using ultrasound. I have wired three 555 circuits in astable mode as in this link (http://www.markallen.com/teaching/ucsd/147a/lectures/lecture4/7.php). Each of the IC's are producing a different high frequency sound centered around 20 khz. So it is not audible but also not too high freq (because down the line I want to be able to decode these by recording it in an ipod or iphone.
I then switch these according to the morse code using digitalWrite on 3 pins of an arduino circuit (i dont want to manually click the the code, but rather but it in arduino's memory and i want it to quickly cycle through this message (each pulse being around 30 to 50 miliseconds). I have the follwoing questions:
1) is this a clever way ?, i dont know if I can use a single 555 circuit and somehow change freqeuncy of this based on dots dashes and spaces (each represented by a unique frequency) rather than using three ic's. If this is possible it would maybe also help with the other problem below
2)There is this terrible clicking noise between pulses as I switch from one 555 to another (all output pins are wired to the same speaker). I tried to build a voltage ramp on supply voltage to the ic's using a diode and a capacitor, it helps a bit but not much (and believe me i tried every cap value from 1pf to 1000mf). I put a low pass rc filter to output, this reduces clicks but also attenuates a lot, so when i amplify again the clciks are back
Can you please help< i've read everything i could find. In the end i either want to create an envelope around the signal so it ramps up and down smoothly between frequency changes, or switch frequencies at exactly zero level voltage during the oscillation. I have tried to read everything I could understand, I am going nuts, please help.
Thanks