Digital to analog conversion. Reads analog signal (voltage) and depending on it, sets the frequency to produce the analog output for sine wave.
Fork of DACandticker_sample by
Diff: main.cpp
- Revision:
- 3:ac3412621bf9
- Parent:
- 2:e27fd3b65155
--- a/main.cpp Wed Jan 24 22:56:54 2018 +0000 +++ b/main.cpp Fri Feb 09 16:35:47 2018 +0000 @@ -11,7 +11,48 @@ #include "sineTable.h" Ticker tick ; // Creates periodic interrupt +Ticker adcTick ; // Creates periodic interrupt AnalogOut ao(PTE30) ; // Analog output +AnalogIn ain(A0) ; // Analog input + +Serial pc(USBTX, USBRX); // tx, rx, for debugging + +// Message type +typedef struct { + uint16_t analog; /* Analog input value */ +} message_t; + +// Mail box +Mail<message_t, 2> mailbox; + +// Function called every 10ms to read ADC +// Low pass filter +// Every 10th value is sent to mailbox +volatile int samples = 0 ; +volatile uint16_t smoothed = 0 ; +void readA0() { + smoothed = (smoothed >> 1) + (ain.read_u16() >> 1) ; + samples++ ; + if (samples == 10) { + // send to thread + message_t *mess = mailbox.alloc() ; // may fail but does not block + if (mess) { + mess->analog = smoothed ; + mailbox.put(mess); // fails but does not block if full + } + samples = 0; + } +} + +// Write voltage digits +// v Voltage as scale int, e.g. 3.30 is 330 +void vToString(int v, char* s) { + s[3] = '0' + (v % 10) ; + v = v / 10 ; + s[2] = '0' + (v % 10) ; + v = v / 10 ; + s[0] = '0' + (v % 10) ; +} // Function called periodically // Write new value to AnalogOut @@ -24,13 +65,41 @@ // Control the frequency of updates // Alternative between two frequencies int main() { + int volts = 0 ; + int counter = 0 ; + char vstring[] = "X.XX\r\n" ; int update_us = 1000 ; // 1ms + int maximum_voltage = 330; + + adcTick.attach_us(callback(&readA0), 10000); // ticks every 10ms + int f = 0; + int old_update_us = update_us; + tick.attach_us(callback(&writeAout), update_us); // setup ticker to write to AnalogOut + while (true) { - tick.attach_us(callback(&writeAout), update_us); // setup ticker to write to AnalogOut - Thread::wait(30000) ; // wait 30 sec - 30000ms - update_us = 2000 ; // 2ms - tick.attach_us(callback(&writeAout), update_us); // setup ticker to write to AnalogOut - Thread::wait(30000) ; // wait 30 sec - 30000ms - update_us = 1000 ; // 1ms + osEvent evt = mailbox.get(); // wait for mail + if (evt.status == osEventMail) { + message_t* mess = (message_t*)evt.value.p ; + volts = (mess->analog * 330) / 0xffff ; + mailbox.free(mess) ; // free the message space + + // change the frequency + f = 1 + (49 * volts / maximum_voltage); + update_us = 1000000 / (f * 64); + + if (update_us != old_update_us) { + tick.attach_us(callback(&writeAout), update_us); // setup ticker to write to AnalogOut + old_update_us = update_us; + } + + vToString(volts, vstring) ; + counter++ ; + if (counter == 10) { // limit bandwidth of serial + pc.printf(vstring) ; + counter = 0 ; + } + } + + Thread::wait(200) ; } }