Can't figure out how to send commands to bluetooth device - react-native

Question

So i've been struggling to implement a bluetooth fingerprint reader that I got from aliexpress. I have looked for 2 days now on how to do it and I am at the stage that I can connect and send stuff. But I have no clue how to do that without having the proper UUID and service. Here is the peripheral Info
{
"characteristics":[
{
"properties":{
"Read":"Read"
},
"characteristic":"2a00",
"service":"1800"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a01",
"service":"1800"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a04",
"service":"1800"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a29",
"service":"180a"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a24",
"service":"180a"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a25",
"service":"180a"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a27",
"service":"180a"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a26",
"service":"180a"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a28",
"service":"180a"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a23",
"service":"180a"
},
{
"properties":{
"Read":"Read"
},
"characteristic":"2a2a",
"service":"180a"
},
{
"properties":{
"Write":"Write",
"Read":"Read"
},
"characteristic":"49535343-6daa-4d02-abf6-19569aca69fe",
"service":"49535343-fe7d-4ae5-8fa9-9fafd205e455"
},
{
"descriptors":[
{
"value":null,
"uuid":"2902"
}
],
"properties":{
"Notify":"Notify",
"Write":"Write"
},
"characteristic":"49535343-aca3-481c-91ec-d85e28a60318",
"service":"49535343-fe7d-4ae5-8fa9-9fafd205e455"
},
{
"descriptors":[
{
"value":null,
"uuid":"2902"
}
],
"properties":{
"Indicate":"Indicate",
"Notify":"Notify"
},
"characteristic":"fff1",
"service":"fff0"
},
{
"properties":{
"Write":"Write",
"WriteWithoutResponse":"WriteWithoutResponse"
},
"characteristic":"fff2",
"service":"fff0"
}
],
"services":[
{
"uuid":"1800"
},
{
"uuid":"180a"
},
{
"uuid":"49535343-fe7d-4ae5-8fa9-9fafd205e455"
},
{
"uuid":"fff0"
}
],
"advertising":{
"txPowerLevel":2,
"serviceData":{
},
"serviceUUIDs":[
"fff0"
],
"localName":"FGT19100003",
"isConnectable":true,
"manufacturerData":{
"bytes":[
2,
1,
2,
12,
9,
70,
71,
84,
49,
57,
49,
48,
48,
48,
48,
51,
3,
3,
240,
255,
2,
10,
2,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0
],
"data":"AgECDAlGR1QxOTEwMDAwMwMD8P8CCgIAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
"CDVType":"ArrayBuffer"
}
},
"rssi":-48,
"id":"88:1B:99:25:AD:54",
"name":"FGT19100003"
But I see characteristic with just 4 chars. Now to my knowledge they have a format of XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX. I have gotten some source code in JAVA that I can upload if anyone wants to have a look at it (it works I installed it and it can scan the fingerprint and gives me the BitMatrix of it back.) (src java project: https://filebin.net/7jeo1o0lkgd8x2oy)
Here is the code for the function that I use in RN.
test(peripheral: { connected: any; id: string; }) {
if (peripheral) {
if (peripheral.connected) {
BleManager.disconnect(peripheral.id);
} else {
BleManager.connect(peripheral.id).then(() => {
let peripherals = this.state.peripherals;
let p = peripherals.get(peripheral.id);
if (p) {
p.connected = true;
peripherals.set(peripheral.id, p);
this.setState({ peripherals });
}
console.log('Connected to ' + peripheral.id);
setTimeout(() => {
BleManager.retrieveServices(peripheral.id).then((peripheralInfo) => {
console.log(JSON.stringify(peripheralInfo))
var service = '49535343-6daa-4d02-abf6-19569aca69fe';
var crustCharacteristic = '49535343-fe7d-4ae5-8fa9-9fafd205e455';
setTimeout(() => {
BleManager.startNotification(peripheral.id, service, crustCharacteristic).then(() => {
console.log('Started notification on ' + peripheral.id);
setTimeout(() => {
BleManager.write(peripheral.id, service, crustCharacteristic, [0]).then(() => {
console.log('write succes');
});
}, 500);
}).catch((error) => {
console.log('Notification error', error);
});
}, 200);
});
}, 900);
}).catch((error) => {
console.log('Connection error', error);
});
}
}
}
Does anyone have experiance with it? I also got a table that states which I think contains all possible commands (https://i.imgur.com/0TP0etn.png).

Answer 1

BLE Services & Characteristics that only have 16-bit UUIDs are the standards ones set by the Bluetooth SIG. They can be found here and here respectively. Most of the characteristics in that list are the standard ones, and I would bet the only one with a 128-bit UUID (0x49535343-fe7d-4ae5-8fa9-9fafd205e455) is the custom service for the finger print data, that or the 0xFFF0 service. They each have some characteristics with indicate/notify, so those are the ones that I imagine would have the data. 0xFFF0 is not a standard UUID, but it is often used in sample codes and implementation examples, but typically shouldn't be in a shipping product, but it has as much chance as being the right characteristic as the other one. I would try making an extra large data buffer, and setting the characteristics to notify/indicate in both services, then do a fingerprint test, and see what you get.
Alternatively, you can use one of the mobile phone BLE debug apps from Nordic (NRFconnect) or Cypress (CySmart) to do the same test and get an idea of the right characteristic by using your phone to perform the same test.