如何使用BLE OBDII外设

Question

我正在尝试创建一个可以从OBDII Bluetooth 4 (LE)设备读取数据的iOS应用程序。我买了一台Vgate icar3蓝牙(4.0) elm327 OBDII。我把它插到我的车里，找到了一些服务广告的IOS-VLink外设。然后，我可以获得这些服务的特征。以下是我找到的服务：

<CBService: 0x1780729c0, isPrimary = YES, UUID = Battery>
<CBService: 0x178072a80, isPrimary = YES, UUID = 1803>
<CBService: 0x178072ac0, isPrimary = YES, UUID = 1802>
<CBService: 0x178072b00, isPrimary = YES, UUID = 1811>
<CBService: 0x178072b40, isPrimary = YES, UUID = 1804>
<CBService: 0x178072b80, isPrimary = YES, UUID = 18F0>
<CBService: 0x178072bc0, isPrimary = YES, UUID = Device Information>
<CBService: 0x178072c00, isPrimary = YES, UUID = E7810A71-73AE-499D-8C15-FAA9AEF0C3F2>

但我不知道1803、1802、1811、1804和18F0服务是什么，也不知道如何使用它们。下面是我用来找出广告内容的简单程序。

class ViewController: UIViewController, CBCentralManagerDelegate, CBPeripheralDelegate {

var centralManager = CBCentralManager()
var peripherals = [CBPeripheral]()
@IBOutlet weak var outputTextView: UITextView!

override func viewDidLoad() {
    super.viewDidLoad()
    centralManager.delegate = self
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}

func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
    print("connected to \(peripheral.name ?? "unnamed")")
    peripheral.delegate = self
    peripheral.discoverServices(nil)
}

func centralManagerDidUpdateState(_ central: CBCentralManager) {
    if central.state == .poweredOn {
        central.scanForPeripherals(withServices: nil, options: nil)
    }
}

func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
    if peripheral.name == "IOS-Vlink" {
        peripherals.append(peripheral)
        print(peripheral.name ?? "peripheral has no name")
        print(peripheral.description)
        central.connect(peripheral, options: nil)
        central.stopScan()
    }

}

func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
    guard let services = peripheral.services else {
        return
    }
    for service in services {
        print(service.description)
        peripheral.discoverCharacteristics(nil, for: service)
    }
}

func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
    guard let chars = service.characteristics else {
        return
    }
    for char in chars {
        print(char.description)
    }
}
}

Answer 1

我想通了。"E7810A71-73AE-499D-8C15-FAA9AEF0C3F2“服务的uuid为"BEF8D6C9-9C21-4C9E-B632-BD58C1009F9F”。如果您为该特征编写一个AT命令，那么它将调用peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?)，然后在value属性中获取结果。下面是发送一个简单的ATZ命令的代码。在这一点上，它只是使用了正确的OBDII ELM327命令。

class ViewController: UIViewController, CBCentralManagerDelegate, CBPeripheralDelegate {

var centralManager = CBCentralManager()
var peripherals = [CBPeripheral]()
@IBOutlet weak var outputTextView: UITextView!

override func viewDidLoad() {
    super.viewDidLoad()
    centralManager.delegate = self
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}

func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
    print("connected to \(peripheral.name ?? "unnamed")")
    peripheral.delegate = self
    peripheral.discoverServices([CBUUID(string:"E7810A71-73AE-499D-8C15-FAA9AEF0C3F2")])
}

func centralManagerDidUpdateState(_ central: CBCentralManager) {
    if central.state == .poweredOn {
        central.scanForPeripherals(withServices: nil, options: nil)
    }
}

func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
    if peripheral.name == "IOS-Vlink" {
        peripherals.append(peripheral)
        print(peripheral.name ?? "peripheral has no name")
        print(peripheral.description)
        central.connect(peripheral, options: nil)
        central.stopScan()
    }

}

func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
    guard let services = peripheral.services else {
        return
    }
    for service in services {
        peripheral.discoverCharacteristics([CBUUID(string:"BEF8D6C9-9C21-4C9E-B632-BD58C1009F9F")], for: service)
    }
}

func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
    guard let chars = service.characteristics else {
        return
    }
    guard chars.count > 0 else {
        return
    }
    let char = chars[0]
    peripheral.setNotifyValue(true, for: char)
    peripheral.discoverDescriptors(for: char)

    print (char.properties)
    peripheral.writeValue("ATZ\r\n".data(using: .utf8)!, for: char, type: CBCharacteristicWriteType.withResponse)

    peripheral.readValue(for: char)
    if let value = char.value {
        print(String(data:value, encoding:.utf8) ?? "bad utf8 data")
    }
}

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
    if let value = characteristic.value {
        print(String(data:value, encoding:.utf8)!)
    }
}
func peripheral(_ peripheral: CBPeripheral, didDiscoverDescriptorsFor characteristic: CBCharacteristic, error: Error?) {
    print(characteristic.descriptors ?? "bad didDiscoverDescriptorsFor")
}
func peripheral(_ peripheral: CBPeripheral, didWriteValueFor characteristic: CBCharacteristic, error: Error?) {
    if let error = error {
        print(error)
    }
    print("wrote to \(characteristic)")
    if let value = characteristic.value {
        print(String(data:value, encoding:.utf8)!)
    }
}
}

Answer 2

如果您在https://www.bluetooth.com/specifications/gatt/services上找到指定的服务，您可以通过服务链接获取有关特征的信息。从服务描述中，可以跟踪特征链接以获取更多信息。

例如: 0x1804服务用于发送功率电平。它是提供org.bluetooth.characteristic.tx_power_level特性的只读服务，如果链接到该特性，则可以看到该特性提供在-100和20之间的带符号8位db电平。

另一个示例:服务0x1811用于警报通知服务。它提供了5个独立的特征: org.bluetooth.characteristic.supported_new_alert_category，org.bluetooth.characteristic.supported_unread_alert_category，org.bluetooth.characteristic.unread_alert_status，、org.bluetooth.characteristic.alert_notification_control_point.和org.bluetooth.characteristic.new_alert服务描述为每个特征提供了简短的解释，并链接到有关该特征的值的更多详细信息。如果您的设备无法通过语音、SMS、IM或电子邮件进行消息传递，则这些特性可能没有意义，也可能不受支持。