Decoding with An O-Scope

[JAndrew]

I'm quite new when it comes to decoding digital signals and I am trying to use my Rigol DS2072 to decode a signal.

I believe the signal follows the RS232 protocol, but the baud rate looks to be 55,550 baud which is an oddball baud.

I've been trying to get my decoding feature to work on the O-Scope but its been a bit of a bugger to try and figure out  some of the settings such as how many bits, whether there is a parity bit, or how many stop bits. I have no information on camera the signal is being sent to, or the unit that the is sending the signal.

Any help would be appreciated. I've attached a screen shot from the O-Scope




Thanks,

Jay

[ataradov]

Do you expect it to be RS232, or UART? Where does this signal come from? Normally UART has idle level high. And RS232 has higher voltage levels.

It is hard to tell from this capture, but it looks like there is also quite a bit of variability in the bit timing.

Try to zoom in close on the first suspected byte and do the decode by hand. Assuming it is 8N1 format, the data appears to be malformed.

[JAndrew]

The plug is a Type Micro-B, I was playing with it a few minutes ago, the image above was generate when the probe was connected to the Data + line, I have subsequently found that if I connect the probed to the Data - I get a far clearer signal. Same signal, just a the picture perfect square waves you'd expect.

This is what throws me off. As you said UART idles High, this idles low. This is the full waveform and it repeats. I suspect the micro controller is querying the camera to see if it's there.

I'll see if I can't maybe decode it by hand. Still working on learning how to decode binary.

Thanks,

Jay

[ataradov]

Is it actually the same signal? Put them both on two different channels and compare.

How often is this sent?

If you provide more information on the actual devices you are probing, we may be able to help you better.

[JAndrew]

I'll get some more screen shots with the set up and what I am trying to do tomorrow. I appreciate the help!

[JAndrew]

Had some more time. I set it back up again and captured a few more images.

There are four wires, Black, Red, Green and White. Black and Red are Ground and Power respectively. Green is Data + (D+) and White is Data - (D-).

The first time I connected the probe to D+ to and Ground and it generated the image as originally attached. I screwed around with that, and couldn't figure much out besides maybe the baud.

The second attempt I connected Channel 1 to D- and Channel 2 to D+. As seen in Capture 2Ch, D- to Ground (Channel 1) provides a much better signal. However it is the same signal as the D+ shown on channel 2.

I tried to make some basic measurements of the length of the data which was 1.69ms (The image shows the cursors kind of funny but the squares are where the measurements were taken)

I zoomed out of the information to try and measure the period between pings. ~57ms (Seen in the Period Between Sends)

Then I thought I might be a bit clever...for kicks and giggles I wonder if perhaps I was measuring it improperly and should have the probe reversed on the D-. The ground clip on the probe was hooked to the D- and the probe was hooked to ground. This inverted the data, and it resembles very much something like a UART wave form. However I don't think this is proper. So I may just be confusing the whole mess.

Here is what I am trying to do. I have a drone that is set up to talk to a camera. The camera busted and I can't get parts anymore, so I am probing to see what signals are sent to from the drone to the camera, and then what signal is sent from the camera to the drone. I am hoping to decode it to a point where I can program an Raspberry Pi zero, or similar MC translate between the camera and the drone.

Hope this provides a clearer picture of whats going on.

Thanks,

Jay

 

[ataradov]

That does not really look like UART. And even i you manage to understand the requests, how do you plan to provide responses without a good camera?

Or this interface on the camera actually works? Are those traces made when the camera is connected?

[JAndrew]

The camera interface is fine. The lens is broken.

I haven’t connected the camera to see what the response is, my first step was to see if I could figure out what how the drone pings the camera


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[ataradov]

Well, it is actually important to see both sides at least to figure out the type of the interface.

[JAndrew]

I didn’t know that.

I’ll see what I can put together.

Thanks


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