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IR communication protocol/design for low latency/fast response - ideas?
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max_torque:

--- Quote from: Corporate666 on May 09, 2019, 06:56:22 pm ---

I don't want to get too much into the application, partly because I have an NDA and also don't want to re-invent the wheel in this thread :)  but basically a robot will move a part from A to B and needs to check the position of the part in-between as it's doing the move and corrects any misalignment prior to loading into B.  These transitions only happen when A is ready to transition to B... so I want the sensor to be in sleep mode and saving battery until the detection needs to happen. The receiver will transmit a wake-up to the sensor which will run until it detects, then go back to sleep.


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To me this sounds rather like the old "if i knew i was going there, i wouldn't have started here" type effect!

If you have  robot doing a task, is it not much more preferential to have it do it's task accurately and in a timely fashion than rely on correcting it's mistakes via some sort of external system?

If i were designing a robot  "to move a part from A to B" i'd make sure that's exactly what it did, and not allow it to swerve off to "C" half way across......   :-DD
ajb:

--- Quote from: max_torque on May 10, 2019, 12:17:09 pm ---
To me this sounds rather like the old "if i knew i was going there, i wouldn't have started here" type effect!

If you have  robot doing a task, is it not much more preferential to have it do it's task accurately and in a timely fashion than rely on correcting it's mistakes via some sort of external system?

If i were designing a robot  "to move a part from A to B" i'd make sure that's exactly what it did, and not allow it to swerve off to "C" half way across......   :-DD

--- End quote ---

Meh, there are lots of situations where it makes a lot more sense to correct for misalignments than to try to prevent them in the first place.  Think about a pick-and-place machine: It's impossible/impractical to package components in tape such that their alignment is guaranteed to the level required for accurate placement, so it's a lot more sensible to just measure the position of the part on the nozzle and then correct.  There's a similar problem with using robots to load/unload mechanical parts from machines: if the part has to sit in a staging area between steps, or worse, get put into a tote and moved to another cell, then you need to incorporate features to very accurately locate the part within that storage or transport system.  Or maybe the tolerance bands on the part itself are too large to accurately locate it mechanically, such as with a raw (metal) casting.  This is a common problem in the CNC machining world, which has to deal with issues of fixture repeatability, raw material tolerances, tool wear, etc, and so has widely adopted electronic probing as a way of measuring and compensating for all sorts of accuracy issues that are impractical (too expensive) to correct any other way.
pwlps:
Here I will comment on my own answer (I find the problem interesting :))

--- Quote from: pwlps on May 10, 2019, 08:01:33 am ---To minimize latency I would suggest to use a differential modulation scheme where no clock synchronisation is needed.  For example see:  https://www.tutorialspoint.com/digital_communication/digital_communication_differential_phase_shift_keying.htm

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The schematics of the DPSK demodulator shown in https://www.tutorialspoint.com/digital_communication/digital_communication_differential_phase_shift_keying.htm
seems incomplete because there is no bandpass filter around the carrier, in real world I suppose what is labeled "DPSK signal" should be an IF (hetorodyned) signal.

But there is another similar differential scheme that does not need any heterodyne stage and that should theoretically have a similar performance : a differential QPSK (DQPSK),  here the phase jumps can be detected by the software so that the analog part of the circuit could only need two chips: a local oscillator and a QPSK demodulator. With the high dynamic range (12 bit,  >1MSPS) of  SAR ADCs of recent Cypress MCUs the analog AGC could be dropped too to optimize latency. Disclaimer: these are only my thoughts based totally on intuitive grounds, I never tested such a circuit.
ogden:

--- Quote from: pwlps on May 10, 2019, 06:27:10 pm ---But there is another similar differential scheme that does not need any heterodyne stage and that should theoretically have a similar performance : a differential QPSK (DQPSK),

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Two incorrect statements :palm:
Heterodyne presence or absence have nothing to do with (de)modulation.
Differential or not, QPSK (4 phase angle encoding, 2 bits/symbol) do not have similar performance to BPSK (2 phase angles, 1 bit/symbol).
You shall update your knowledge ASAP. Start here: https://en.wikipedia.org/wiki/Phase-shift_keying
pwlps:

--- Quote from: ogden on May 10, 2019, 07:36:06 pm ---
--- Quote from: pwlps on May 10, 2019, 06:27:10 pm ---But there is another similar differential scheme that does not need any heterodyne stage and that should theoretically have a similar performance : a differential QPSK (DQPSK),

--- End quote ---

Two incorrect statements :palm:
Heterodyne presence or absence have nothing to do with (de)modulation.
Differential or not, QPSK (4 phase angle encoding, 2 bits/symbol) do not have similar performance to BPSK (2 phase angles, 1 bit/symbol).
You shall update your knowledge ASAP. Start here: https://en.wikipedia.org/wiki/Phase-shift_keying

--- End quote ---

Ok thanks for correcting me. I understand very well all the underlying maths and don't need your explanations, but sorry if my own explanation or wording was not precise.


--- Quote from: ogden on May 10, 2019, 07:36:06 pm ---Heterodyne presence or absence have nothing to do with (de)modulation.

--- End quote ---

It has a lot,  at least from the signal analysis point of view.

I don't want to go further in this kind of discussion, I give here a physicist' way of thinking, and you have an EE point of view, but you won't get any point attacking me on that.  Please take it easy and focus on electronics.





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