Core Bluetooth - Communicate with LED Light

Question

I am working on Core Bluetooth communicate with LED Light. When peripheral write the value to communication, take some time to get response from hardware(LED).As we are using UISLider to write values we are facing delay in hardware. I think a queue occur whenever we are moving slider fast. How can i fix this delay?

    let slider0:UInt8 = UInt8(sliderBrightness.value) // Brightness
    let slider1:UInt8 = UInt8(mode) // Mode
    let slider2:UInt8 = UInt8(sliderDirection.value) // Direction
    let slider3:UInt8 = UInt8(sliderStrength.value) // Strength
    let slider4:UInt8 = UInt8(sliderWhite.value) // Neutral LED Dimming
    let slider5:UInt8 = UInt8(sliderOrange.value) // Warm LED Dimming
    let slider6:UInt8 = UInt8(mode == 3 ? sliderOrbit.value : sliderOnTime.value)  // According to Mode
    let slider7:UInt8 = UInt8(sliderOffTime.value) // According to Mode
    let slider8:UInt8 = UInt8(255)
    let buff: [UInt8] = [slider0,slider1,slider2,slider3,slider4,slider5,slider6,slider7,slider8]
    
    let data = Data(bytes: buff, count: buff.count)
    let sliderVal = Int(sender?.value ?? 0.0)
    guard let char  = ledChar else {return}
    if sender == nil || sliderVal % 1 == 0 {
        print(sliderVal)
        
        if sender != nil, previousValue == sliderVal {
            return
        }
        previousValue = sliderVal
        pendingRequestWorkItem?.cancel()

        let requestWorkItem = DispatchWorkItem { [weak self] in
            self?.writeLEDValueToChar( withCharacteristic: char, withValue: data)
        }

        pendingRequestWorkItem = requestWorkItem
        DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(12),
                                      execute: requestWorkItem)

@Larme When i am using slider to write values to ble hardware, hardware is taking a delay to reflect the output. — Balkaran, Dec 01 '21 at 11:32
@MichaelKotzjan It depend on how frequently i move the slider. If i give a single write input value to hardware it works fine but in case of slider user can move slider very frequently and delay is coming — Balkaran, Dec 01 '21 at 11:44
That sounds like the `DispatchQueue` is your problem. You put every new value into this queue for it to be send to the device. BLE is not fast enough to to handle your real time data. — Michael Kotzjan, Dec 01 '21 at 11:46
@MichaelKotzjan can you suggest any way to handle this situation without using dispatch queue? — Balkaran, Dec 01 '21 at 11:48

score 1 · Accepted Answer · answered Dec 03 '21 at 05:44

1

One thing you could try would be to get rid of the dispatch queue all together and write the value directly. Of course, some values will not be written since the phone will still be handling the last value transmission. You could simply ignore this error. Something like this could do the trick:

if sender == nil || sliderVal % 1 == 0 {
    print(sliderVal)
        
    if sender != nil, previousValue == sliderVal {
        return
    }
    previousValue = sliderVal
    writeLEDValueToChar( withCharacteristic: char, withValue: data)
}

Another way could be to not use every possible value from the slider by setting the step width of the slider:

Slider(
    value: $speed,
    in: 0...100,
    step: 5
)

This way you would get only the values 0, 5, 10, 15, ... instead of 0.0000, 0.0001, 0.0002, ... which would decrease the amount of entries in the DispatchQueue while moving the slider

answered Dec 03 '21 at 05:44

Michael Kotzjan

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Thanks your valuable response. Actually I already implemented this trick. Now I am using didwritevalue method to pass the latest value when hardware is free. It is working fine with this logic also. – Balkaran Dec 03 '21 at 07:19
1

Great to hear you managed well on your own. Since you are now skipping some values, do you see the difference on your LED? Do you get visible less smooth transitions when changing the value? – Michael Kotzjan Dec 03 '21 at 07:54
Clockwise and Anti-Clockwise transition is not smooth When I skipped values, rest of controls are working fine like brightness, color changing. So I have Implemented above comment logic. – Balkaran Dec 03 '21 at 08:04
Very interesting, thanks for sharing! – Michael Kotzjan Dec 03 '21 at 08:19

Core Bluetooth - Communicate with LED Light

1 Answers1