Hello,
After a successful BLE.connect() to a BLE device, I am unable to read that device's characteristics. This always returns false:
peer.getCharacteristicByUUID(myChar, BleUuid("4149524C-03B7-0014-0004-000000000000"));
I know the UUID is correct as I have a smartphone app that connects to it and reads it just fine.
Does anyone have any code that can print / enumerate / list all of the services and characteristics on a particular connected peer?
Thanks.
Here is some code I am using to test the connection.
// Turn on all logging
SerialLogHandler logHandler(LOG_LEVEL_ALL);
// Global variables
BleCharacteristic ble_char;
const BleUuid ble_charUuid("4149524C-03B7-0014-0004-000000000000");
BleScanResult ble_scanResult;
BlePeerDevice ble_peer;
BleScanResult ble_devices[30];
int ble_devices_seen = 0;
// Setup
void setup() {
// Start logging
Log.info("Starting...");
}
// Loop
void loop() {
// Scan for nearby devices
ble_devices_seen = BLE.scan(ble_devices, 30);
Log.info("BLE devices: %u", ble_devices_seen);
// Check each seen device
for (int x = 0; x < ble_devices_seen; x++) {
BleScanResult scanResult = ble_devices[x];
// Is this device we are looking for?
if (scanResult.address[5] == 0xF4 && scanResult.address[4] == 0x03 && scanResult.address[3] == 0xB7 &&
scanResult.address[2] == 0x62 && scanResult.address[1] == 0xB7 && scanResult.address[0] == 0x86) {
// Connect to it
ble_peer = BLE.connect(scanResult.address);
if (ble_peer.connected()) {
Log.info("connected");
// Attempt to read the characteristic
if (ble_peer.getCharacteristicByUUID(ble_char, ble_charUuid)) {
Log.info("read characteristic");
} else {
Log.info("failed to read characteristic");
}
// Disconnect
BLE.disconnect(ble_peer);
Log.info("disconnected");
} else {
Log.info("connection failed");
}
}
}
// Try every 10 seconds
delay(10000);
}
This is the serial log output from running the above program:
0000046248 [app] INFO: Starting...
0000072109 [app] INFO: BLE devices: 24
0000072322 [wiring.ble] TRACE: New peripheral is connected.
0000072323 [wiring.ble] TRACE: Start discovering services.
0000072684 [wiring.ble] TRACE: Start discovering characteristics.
0000074844 [app] INFO: connected
0000074944 [app] INFO: failed to read characteristic
0000075114 [app] INFO: disconnected
On the peripheral device, I can see the connection being made, the MTU being negotiated, but I never see a characteristic being read.
Further troubleshooting shows that 2-byte characteristics (such as 0x2A00 - Device name) can be read successfully. I am unable to read 128-bit UUID custom characteristics. All from the same peripheral device.
Not sure why that wouldn't work, but you could investigate the ble_peer.discoverAllCharacteristics() vector to see whether your particular chararcteristic shows up at all (and where the discrepancy may come from).
Can you post a screenshot of the UUID discoverd by your smartphone?
Thanks ScruffR,
This is not a scren shot, but here is the service/characteristic configuration.
UUID (0x1800) - Generic Access Services
+ UUID (0x2A00) - Device name characteristic (19-bytes r)
+ UUID (0x2A01) - Appearance characteristic (2-bytes r)
+ UUID (0x2A04) - Connection parameters characteristic (8-bytes r)
UUID (0x1801) - Generic Attribute Service
+ UUID (0x2A05) - Service changed characteristic (4-bytes r)
UUID (4149524C-03B7-0014-0004-000000000000) - Custom primary service
+ UUID (4149524C-03B7-0014-0004-000000000001) - Status characteristic (128-bytes r)
+ UUID (4149524C-03B7-0014-0004-000000000002) - Command characteristic (20-bytes rw)
+ UUID (4149524C-03B7-0014-0004-000000000003) - Long command characteristic (132-bytes rw)
I will take a look at the vector you suggested and see what data is in there. I assume that the Particle system supports multiple services with multiple characteristics.
Thanks.
I see there is no characteristics that ends on 000000000000 only the service does.
To have getCharacteristicsByUUID() to work with 128bit UUIDs you have to have an exact match.
Ah yes, you were correct. I had the service UUID in there and no the characteristic. Oh well, not all is lost. I wrote some code to scan nearby BLE devices and then read all of the characteristics from a particular one. Maybe someone will find this useful.
// Set the MAC address of the BLE device we want to scan
#define BLE_PEER_ADDRESS {0x86, 0xB7, 0x62, 0xB7, 0x03, 0xF4}
// Turn on all logging
SerialLogHandler logHandler(LOG_LEVEL_ALL);
// Global variables
Vector<BleCharacteristic> ble_peer_all_chars;
BleCharacteristic ble_char;
char ble_char_uuid_string[40];
byte ble_char_value[250];
char ble_char_value_string[501];
BlePeerDevice ble_peer;
int ble_peer_found_at = -1;
const BleAddress ble_peer_address = BleAddress(BLE_PEER_ADDRESS);
BleScanResult ble_devices[30];
int ble_devices_seen = 0;
// Setup
void setup() {
// Start logging
Log.info("Starting...");
}
// Loop
void loop() {
// Start
Log.info("Scanning for nearby BLE devices...");
// Scan for nearby devices
ble_devices_seen = BLE.scan(ble_devices, 30);
Log.info(" - devices visible: %u", ble_devices_seen);
// List nearby devices
for (int x = 0; x < ble_devices_seen; x++) {
BleScanResult scanResult = ble_devices[x];
Log.info(" %s %idB", ble_devices[x].address.toString().c_str(), ble_devices[x].rssi);
}
// Look for the device we want to connect to.
for (int x = 0; x < ble_devices_seen; x++) {
if (strncmp(ble_devices[x].address.toString(), ble_peer_address.toString(), 17) == 0) {
ble_peer_found_at = x;
Log.info("Found matching device %s at position %i", ble_devices[ble_peer_found_at].address.toString().c_str(), ble_peer_found_at);
// Connect to this peer
Log.info(" - Connecting");
ble_peer = BLE.connect(ble_devices[ble_peer_found_at].address);
if (ble_peer.connected()) {
Log.info(" - Connection successful");
// Read all of the advertised characteristics
ble_peer_all_chars = ble_peer.discoverAllCharacteristics();
if (ble_peer_all_chars.size()) {
Log.info(" - Characteristics found: %u", ble_peer_all_chars.size());
// Read and display each characteristic
for (int y = 0; y < ble_peer_all_chars.size(); y++) {
// Display header for short characteristics
if (ble_peer_all_chars[y].UUID().type() == BleUuidType::SHORT) {
bin2hex(&ble_peer_all_chars[y].UUID().rawBytes()[0], &ble_char_uuid_string[0], 2, 1);
Log.info(" SHORT 0x%s", ble_char_uuid_string);
}
// Display header for long characteristics
if (ble_peer_all_chars[y].UUID().type() == BleUuidType::LONG) {
bin2hex(&ble_peer_all_chars[y].UUID().rawBytes()[12], &ble_char_uuid_string[0], 4, 1);
ble_char_uuid_string[8] = '-';
bin2hex(&ble_peer_all_chars[y].UUID().rawBytes()[10], &ble_char_uuid_string[9], 2, 1);
ble_char_uuid_string[13] = '-';
bin2hex(&ble_peer_all_chars[y].UUID().rawBytes()[8], &ble_char_uuid_string[14], 2, 1);
ble_char_uuid_string[18] = '-';
bin2hex(&ble_peer_all_chars[y].UUID().rawBytes()[6], &ble_char_uuid_string[19], 2, 1);
ble_char_uuid_string[23] = '-';
bin2hex(&ble_peer_all_chars[y].UUID().rawBytes()[0], &ble_char_uuid_string[24], 6, 1);
Log.info(" LONG %s", ble_char_uuid_string);
}
// Read the characteristic (only the first 20 bytes)
if (ble_peer.getCharacteristicByUUID(ble_char, ble_peer_all_chars[y].UUID())) {
ble_char.getValue(ble_char_value, 20);
bin2hex(ble_char_value, ble_char_value_string, 20, 0);
Log.info(" [ %s ]", ble_char_value_string);
} else {
Log.info(" [ Could not read ]");
}
}
}
// Disconnect from the peer
BLE.disconnect(ble_peer);
Log.info(" - Disconnected");
} else {
Log.info(" - Could not connect to the device");
}
}
}
// Let us know if a match was not found
if (ble_peer_found_at == -1) Log.info("No matching device was found");
// Wait 60 seconds and then try again
delay(60000);
}
// ==============================================================
// bin2hex
// ==============================================================
int bin2hex(const byte *input, char *output, int len, int reverse) {
// Check if we have data to convert
if (input == NULL || output == NULL || len == NULL) return 0;
// Step through each byte
for (int i = 0; i < len; i++) {
if (reverse == 1) {
output[i * 2] = "0123456789ABCDEF"[input[len - (i + 1)] >> 4];
output[i * 2 + 1] = "0123456789ABCDEF"[input[len - (i + 1)] & 0x0F];
} else {
output[i * 2] = "0123456789ABCDEF"[input[i] >> 4];
output[i * 2 + 1] = "0123456789ABCDEF"[input[i] & 0x0F];
}
}
output[len * 2] = '\0';
// Return
return 1;
}
My take on this issue is that it is related to the Bluetooth version you are running. For example, iPhone 8 and above use 5.0, can connect but don’t read characteristics. iPhone 7 and below use Bluetooth 4.2 and work OK. I am yet to confirm whether this is an issue with Apple devices or Particle devices?
what works for me . . .
from my post here . . .