I chose to use a micro planning future updates, such as turn on or off the light with 2 claps, the TV with 3 claps, DVD player with 4 and so on. Another update can be a time to turn off the device automatically.
The signal is captured by the mic and amplified by the transistor (BC548), this signal run through a lowpass filter that remove the high frequencies and go to ATmega8 ADC. To keep the circuit simple, only one transistor is used on signal amplification. Two buttons are used to up or down the sensibility of the signal. You can see the complete schematic below. The components on dotted line are optional.
The circuit can be powered with 7 ~ 12V and the relay must be for that voltage.
So, the user can increase or decrease the intensity of the signal necessary to trigger the circuit. If the value of the ADC is less than the variable, nothing happens, otherwise the timer0 is activated and begins counting. At each timer overflow, a variable called timer is incremented.
The value of variable timer is compared with three constants, burst_time, ready_time and time_out. If the value of the variable is equal to the constant burst_time the value of global variable burst become 1. If the value of timer is equal the constant ready_time the value of variable burst becomes 0 and variable ready becomes 1. If value of timer is equal time_out all the variables become equal to 0.
When another clap is detected, if burst = 1 then the microcontroller clear all variables and start the loop again. If burst = 0 and ready = 1 the output is toggled.
The relay only close when the time between a clap and another is approximately correct, thus reducing the chances of the light turn on or off accidentally.
The flowchart below help understand the software.
The USART is used to debug the code and help understand how the software works.
The hyper terminal config
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