glitch counter

[thanhTran]

What's the algorithm behind counting glitch?

In which section that a glitch counter is applied to in the following sequence

a. From RX to the PPM/PCM decoder chip?
b. From the decoder chip to servos/esc?

I've always thought that we look at the signal and if the pulse width is longer than 2.2 ms or shorter than 1ms, BUT, I've seen glitches in my radio set up, in which there are servo movements but there is no TX input and the servo movement are well within range.

So, how do you count glitch? :)

Thanks very much for your thoughts and your answers

Thanh

[Bruce Abbott]

The best place to detect glitches is just before (or inside) the decoder. After decoding, some signal quality information is lost and the rest is annoyingly spread out over the separate servo outputs.

Just because servo movements are small does not mean that the glitches are inside the range of acceptance. It takes time for a servo to move, and many consecutive anomalous pulses are probably required before it hits its stops.

Varying pulse widths that are inside the range of acceptance could be glitches, or they could be normal control signals. There is no way to know for sure unless you can compare it to a noise-free version of the transmitted signal (even if no stick was moved, the transmitter could still be the source!).

Anyway, small glitches don't cause much trouble. The problem is big glitches that cause the decoder to lose sync and throw out wildly anomalous pulses, and/or mix the channels up. Just doing a basic sanity check on the signal will avoid most of these errors.

[thanhTran]

Hi Bruce,

Thank you very much for the well thought & explained inputs. The servo movement you explained really makes sense to me and therefore I could put a glitch counter on the servo line (the only access I have)

The reason I ask this because I've been trying to isolate the glitch I see with 2 Shadow 3 RXes I have in hand, and without a glich counter, I see it's hard to do. So probably I'll build one :)

Best regards,

Thanh

ps. I've read your smart PPM decoder for 4CH & 6CH. they were really great! :). Great work!