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doc: add interpretation

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King Kévin 2024-03-18 23:37:49 +01:00
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README.md
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The USB micro-B and C cable tester identifies functionalities supported by USB cables. The USB micro-B and C cable tester identifies capabilities supported by USB cables and deduces it's purpose.
It helps figuring out if a USB cable is for charging or to transfer data. It helps figuring out if a USB cable is for charging or to transfer data, and at which speed.
It supports type A to micro-B, A to C, and C to C USB cables. It supports type A to micro-B, A to C, and C to C USB cables.
usage usage
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- ensure the tester has a non-empty battery in the CR2032/2025, or is externally powered through the USB power port - ensure the tester has a non-empty battery in the CR2032/2025, or is externally powered through the USB power port
- plug one end of the cable in one of the host ports - plug one end of the cable in one of the host ports
- plug the other end of the cable in one of the devices ports - plug the other end of the cable in one of the devices ports
- the tester will identify the cable's capabilities - the tester will identify the cable's capabilities, on the left side
- the tester will then show the cable's purpose, on the right side
To understand further the capabilities and purpose of a cable, I recommend reading the USB specification, mainly the one for the [type-C connector](https://www.usb.org/document-library/usb-type-cr-cable-and-connector-specification-release-23).
design choice design choice
============= =============
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- C to C: often used for high power charging of phones and laptops - C to C: often used for high power charging of phones and laptops
- battery operated: it's a very simple device, and this avoids needing to require external power - battery operated: it's a very simple device, and this avoids needing to require external power
- power port: in case you have no battery or it runs out - power port: in case you have no battery or it runs out
- USB 3.0: because it is hard to identify if C-C cable support Super-Speed - USB 3.0: because it is hard to identify if C-C cable support SuperSpeed
- purpose: deduce from capabilities
don't: don't:
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- A or micro-B 3.0: the connectors that support it are obvious, and it's rare they are used for anything else than Super-Speed transfer (plus they are less common or problematic) - A or micro-B 3.0: the connectors that support it are obvious, and it's rare they are used for anything else than Super-Speed transfer (plus they are less common or problematic)
- Power Delivery capabilities: this requires complex host software communicating with the eMarker chip in the cable - Power Delivery capabilities: this requires complex host software communicating with the eMarker chip in the cable
- OTG: even if detecting this functionality is easy, micro-B OTG adapters are not popular anymore - OTG: even if detecting this functionality is easy, micro-B OTG adapters are not popular anymore
- impedance: only the presence of wires is tester, not their impedance
future: mode of operation
-----------------
- interpret the supported functionalities to show the cable purpose Most of the tests just verify if the wires corresponding to capabilities are present in the cable.
- show a simple cable type result, and not just the individual capabilities Some additional tests verify the resistances in the plugs.
For more details, check the schematic, and refer to [type-C specification](https://www.usb.org/document-library/usb-type-cr-cable-and-connector-specification-release-23).
The left side identifies the capabilities.
Based on that, a micro-controller (MCU) with map the combination into a purpose on the right side.
The left side if independent of the MCU and right side.
limitation
----------
The tester does not:
- verify the resistance of wires, particularly the power ones
- verify the impedance of wires, particularly the differential ones
- verify if the shield(s) is more than just a wire
- read out capabilities from electronically marked cables
- guarantee USB cable compliance or conformity, as this is [very complex](https://www.usb.org/documents?search=&category%5B%5D=49&type%5B%5D=56&tid_2%5B%5D=41&items_per_page=50)
alternatives alternatives
------------ ------------