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Topic: Oscilloscope output to circuit logic.  (Read 187 times) previous topic - next topic

jackjameshoward

Nov 27, 2020, 03:12 pm Last Edit: Nov 27, 2020, 03:15 pm by jackjameshoward
I captured some waveforms via an oscilloscope at point RXD_0 (referring to the schematic attached, isolator in the centre of the schematic.)
I have modified the waveform and want to inject it back into the circuit via the Arbitrary Waveform generator on the oscilloscope at point TXD_0.
From my understanding, the default state of TXD_0 is logic high (3v3) and needs to be pulled low to transmit data.
Can anybody tell me how I can achieve this using the arb gen on the oscilloscope?

The circuit is an off the shelf board, but I don't mind modifying it, and I can also make an additional circuit if needed.
https://www.picotech.com/oscilloscope/4824/picoscope-4824-specifications

https://www.waveshare.com/w/upload/1/15/2-CH-CAN-HAT-Schematic.pdf
https://www.waveshare.com/w/upload/8/83/MCP2515.pdf
https://www.waveshare.com/w/upload/8/82/SN65HVD230.pdf
https://www.silabs.com/documents/public/data-sheets/si864x-datasheet.pdf


Any advice is much appreciated, thanks in advance.

aarg

"inject"? Are you planning on cutting and lifting traces?
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

TomGeorge

#2
Nov 27, 2020, 03:44 pm Last Edit: Nov 27, 2020, 03:46 pm by TomGeorge
Hi,
Please post schematics a exported images in jpg, some platforms have difficulty displaying pdfs.
Ops schematic.


Tom... :)
PS, Sorry where is the Arduino?
Everything runs on smoke, let the smoke out, it stops running....

Smajdalf

Not looking into any of the included files I guess it is digital signal. I would try to decode the protocol and recreate it using Arduino, not a function generator.

jackjameshoward

#4
Nov 27, 2020, 03:53 pm Last Edit: Nov 27, 2020, 03:54 pm by jackjameshoward
If need I can cut the traces.
I'm basically using the board for the isolation and the CAN transceiver.
I'm not really using the CAN decoder IC.
I want to use the oscilloscope to simulate the logic RX that the CAN decoder would usually output.

Tom,
The Arduino uses the SPI Header 9

Smajdalf,
There are several problems with the using the Arduino, for now. The CAN frames are none standard and I need to decode them; hence using the scope, modifying the waveforms and returning that back into the data stream to help in the decoding process.

Smajdalf

The EN pins of the isolator are not connected in the schematic. Maybe you could pull it LOW to disable outputs of the isolator and inject your own signals?

MarkT

This is a question perhaps best aimed at a forum for the make of 'scope you have, not an Arduino forum as
its about using the interface on a particular oscilloscope.

What I can say is signal generators have an output impedance, typically 50 or 600 ohms, or perhaps
selectable, and interfacing that into an existing circuit may require some active components.

You've not circled the relevant portion of that large circuit diagram - few of us enjoy playing hunt the
named signal like this, make it easy to help you...
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

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