利用MAXQ7667确定超声传感器的谐振频率和阻尼特性

　　// LPFD reading that is 70% of the peak reading.

　　for (i = 0; i number_of_steps; i++)

　　{

　　if (lpfdata[i] > peak*0.7)

　　{

　　first70 = i;

　　i = number_of_steps;

　　}

　　}

　　for (i = number_of_steps; i >0; i--)

　　{

　　if (lpfdata[i] > peak*0.7)

　　{

　　second70 = i;

　　i= 1;

　　}

　　}

　　i = (first70 + second70)/2; // i = the loop value at the center frequency.

　　center_pllf = i*step_size; // Set PLLF_bit.PLLF to this value for the resonant frequency.

　　//Remeasure damping using the center frequency.

　　damp_time = damping_half_time(center_pllf, 75);

　　// At this point there are three valuable pieces of information about the transducer.

　　// Peak = the peak value from the frequency sweep.

　　// center_pllf = the PLLF setting at the resonant frequency.

　　// damp_time = time for the resonance to decay to 1/2 the peak value.

　　center_burst_frequency = 16000000/Burst_Clock_Divider*(center_pllf+768)/1024;

　　SendData();

　　} // While(1)

　　} // End Main