Problem with Manchester encoded RC5

gwolf · Post by **gwolf** » Tue Dec 13, 2022 9:45 am

Manchester serial decoding does not work for the output signal from my TSOP33436 IR receiver (RC5 protocol). Instead of positioning the first bit at the first transition (which is from +5V to 0) it does so at the second transition. The results are wrong packet length (13 bit instread of 14) and wrong data.

PicoScope® 6 - PC Oscilloscope software version: 6.14.61.6219
Model: PicoScope 2204A

Post by **Martyn** » Mon Dec 19, 2022 6:12 am

Can you supply a psdata file so that we can see the issue.

gwolf · Post by **gwolf** » Mon Dec 19, 2022 10:57 am

RC5.psdata: (16.88 KiB) Downloaded 78 times

Post by **Martyn** » Mon Dec 19, 2022 1:58 pm

I have raised this for investigation by the team, it looks as if we may not be detecting the first edge as the start bit so end up being 1/2 a bit out throughout.

bennog · Post by **bennog** » Mon Dec 19, 2022 7:24 pm

I think the start flank is missing in this signal.

Every example I have found has a halfway signal when idle and has a edge half the amplitude as a start of package timing trigger. Also if you count the full bits then you see the first bit should have a staring edge before the first edge.
Something I have added in red in the below scope image.

I have also exported to sigrok and gave the same inconsistend timing result.

gwolf · Post by **gwolf** » Mon Dec 19, 2022 9:08 pm

Perhaps our problem is that Manchester encoded signals look different on a data line (no DC component) than on the output of an IR receiver (idle = 5V).

gwolf · Post by **gwolf** » Fri Jan 06, 2023 8:47 pm

I suppose that we dealing here with logic systems, where a halfway level does not exist.
Any results from your investigation?

jsimon669 · Post by **jsimon669** » Mon Mar 20, 2023 4:15 pm

Any update on this? It seems I am having the exact same problem where the first edge is missed and throws the entire decoding off.

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