I am using adafruit feather nrf52840 sense with a customized EMG amplifier (Analog input), and Mic (Analog input). And, I want to plot the data on the mobile application. But, the maximum sampling rate calculated by "millis()" was only 630 Hz.
Could you please check my code and give me some comments to increase the sampling rate? I want to get about a 1 kHz sampling rate. And, also could you please recommend a mobile application to plot and save the received data? Now, I used Bluefruit LE Connect but there is no data save function.
Thank you.
#include <bluefruit.h>
#include <Adafruit_LittleFS.h>
#include <InternalFileSystem.h>
// BLE Service
BLEDfu bledfu; // OTA DFU service
BLEDis bledis; // device information
BLEUart bleuart; // uart over ble
BLEBas blebas; // battery
bool BLEisConnected = false;
unsigned long time_start = 0;
void setup()
{
Serial.begin(115200);
#if CFG_DEBUG
// Blocking wait for connection when debug mode is enabled via IDE
while ( !Serial ) yield();
#endif
Serial.println("Bluefruit52 BLEUART Example");
Serial.println("---------------------------\n");
// Setup the BLE LED to be enabled on CONNECT
// Note: This is actually the default behavior, but provided
// here in case you want to control this LED manually via PIN 19
Bluefruit.autoConnLed(true);
// Config the peripheral connection with maximum bandwidth
// more SRAM required by SoftDevice
// Note: All config***() function must be called before begin()
Bluefruit.configPrphBandwidth(BANDWIDTH_MAX);
Bluefruit.begin();
Bluefruit.setTxPower(4); // Check bluefruit.h for supported values
//Bluefruit.setName(getMcuUniqueID()); // useful testing with multiple central connections
Bluefruit.Periph.setConnectCallback(connect_callback);
Bluefruit.Periph.setDisconnectCallback(disconnect_callback);
// To be consistent OTA DFU should be added first if it exists
bledfu.begin();
// Configure and Start Device Information Service
bledis.setManufacturer("Adafruit Industries");
bledis.setModel("Bluefruit Feather52");
bledis.begin();
// Configure and Start BLE Uart Service
bleuart.begin();
// Start BLE Battery Service
blebas.begin();
blebas.write(100);
// Set up and start advertising
startAdv();
Serial.println("Please use Adafruit's Bluefruit LE app to connect in UART mode");
Serial.println("Once connected, enter character(s) that you wish to send");
}
void startAdv(void)
{
// Advertising packet
Bluefruit.Advertising.addFlags(BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE);
Bluefruit.Advertising.addTxPower();
// Include bleuart 128-bit uuid
Bluefruit.Advertising.addService(bleuart);
// Secondary Scan Response packet (optional)
// Since there is no room for 'Name' in Advertising packet
Bluefruit.ScanResponse.addName();
/* Start Advertising
* - Enable auto advertising if disconnected
* - Interval: fast mode = 20 ms, slow mode = 152.5 ms
* - Timeout for fast mode is 30 seconds
* - Start(timeout) with timeout = 0 will advertise forever (until connected)
*
* For recommended advertising interval
* https://developer.apple.com/library/content/qa/qa1931/_index.html
*/
Bluefruit.Advertising.restartOnDisconnect(true);
Bluefruit.Advertising.setInterval(32, 32); // in unit of 0.625 ms
Bluefruit.Advertising.setFastTimeout(30); // number of seconds in fast mode
Bluefruit.Advertising.start(0); // 0 = Don't stop advertising after n seconds
}
void loop()
{
// Forward data from HW Serial to BLEUART
while (BLEisConnected)
{
// Delay to wait for enough input, since we have a limited transmission buffer
//delay(500);
char buf[1500];
String value ="";
for (int i = 0; i<=100; i++)
{
time_start = millis();
// Read value from pin A0 of the nRF52832
analogReadResolution(8); // 0-255
uint8_t num = analogRead(A1); // unsigned char: 0-255 ( 1 byte)
uint8_t num2 = analogRead(A5); // unsigned char: 0-255 ( 1 byte)
value += String(time_start);
value += ",";
value += String(num);
value += ",";
value += String(num2);
value += "\n";
}
// Convert String into an array of characters that will be stored in "buf"
value.toCharArray(buf, 1500);
// Send the buf (character array) via BLE
bleuart.write( buf, strlen(buf) );
}
}
// callback invoked when central connects
void connect_callback(uint16_t conn_handle)
{
// Get the reference to current connection
BLEConnection* connection = Bluefruit.Connection(conn_handle);
char central_name[32] = { 0 };
connection->getPeerName(central_name, sizeof(central_name));
Serial.print("Connected to ");
Serial.println(central_name);
BLEisConnected = true;
}
/**
* Callback invoked when a connection is dropped
* @param conn_handle connection where this event happens
* @param reason is a BLE_HCI_STATUS_CODE which can be found in ble_hci.h
*/
void disconnect_callback(uint16_t conn_handle, uint8_t reason)
{
(void) conn_handle;
(void) reason;
Serial.println();
Serial.print("Disconnected, reason = 0x"); Serial.println(reason, HEX);
BLEisConnected = false;
}