69 lines
1.9 KiB
JavaScript
69 lines
1.9 KiB
JavaScript
async function connect(props) {
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const device = await navigator.bluetooth.requestDevice({
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filters: [{ services: ["cycling_speed_and_cadence"] }],
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acceptAllDevices: false,
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});
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console.log(`%c\n👩🏼⚕️`, "font-size: 82px;", "Starting CSC...\n\n");
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const server = await device.gatt.connect();
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const service = await server.getPrimaryService("cycling_speed_and_cadence");
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const char = await service.getCharacteristic("csc_measurement");
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char.oncharacteristicvaluechanged = props.onChange;
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char.startNotifications();
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return char;
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}
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function parseCSC(e) {
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const flags = e.target.value.getUint8(0, true);
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const hasWheel = !!(flags & 0x01);
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const hasCrank = !!(flags & 0x02);
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let index = 1;
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const res = {
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wheelRevs: null,
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wheelTime: null,
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crankRevs: null,
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crankTime: null,
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};
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if (hasWheel) {
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res.wheelRevs = value.getUint32(index, true);
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index += 4;
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res.wheelTime = value.getUint16(index, true);
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index += 2;
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}
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if (hasCrank) {
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res.crankRevs = value.getUint16(index, true);
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index += 2;
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res.crankTime = value.getUint16(index, true);
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index += 2;
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}
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console.log("CSC", res);
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const pre = document.createElement("pre");
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pre.style.border = "1px solid red";
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pre.textContent = JSON.stringify(res, null, 2);
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document.body.appendChild(pre);
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return res;
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}
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function revsToRPM(t1, t2) {
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const deltaRevs = t2.revs - t1.revs;
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if (deltaRevs === 0) {
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// no rotation
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return 0;
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}
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let deltaTime = (t2.time - t1.time) / 1024;
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if (deltaTime < 0) {
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// time counter wraparound
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deltaTime += Math.pow(2, 16) / 1024;
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}
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deltaTime /= 60; // seconds to minutes
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const rpm = deltaRevs / deltaTime;
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return rpm;
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}
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document.querySelector("#ble-connect").addEventListener("click", () =>
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connect({
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onChange: parseCSC,
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}).catch(console.error)
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);
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