describe project in README
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README.md
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README.md
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these are the hardware design files for **insert project name here**.
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these are the hardware design files for the USB bug detector.
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purpose
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purpose
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=======
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the purpose of the USB bug detector is to identify USB cables (or devices) with integrated circuits.
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usage
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usage
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=====
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to use the USB bug detector, follow the steps provided on the back of the board:
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- insert a CR2025 or CR2032 coin cell battery in the USB bug detector for it to be operational
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- press on the RESET button to arm the test
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- the BUGGED LED should be off
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- plug the USB cable in the USB receptacle
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- if the BUGGED LED switches on, the USB cable embeds an integrated circuit (e.g. a bug)
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- if the BUGGED LED remains off, the cable is same to use
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after the test, to save power, press again on the RESET button.
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to ensure that the USB bug detector works, after pressing on the RESET button, press on the TEST button.
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this will simulate a USB plug with integrated circuit.
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the BUGGED LED should switch on.
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this also ensures the battery is not empty.
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fabrication
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===========
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the board has an optional READY LED (with accompanying resistor located next to it).
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only populate it to debug the board.
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the READY LED will we on when the BUGGED LED isn't.
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this allows to always check if the battery is empty, but this also drains the battery even when not testing because an LED is always on.
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the first prototype of the board (v0.3) offer three populating options, depending on the available NOR gate part:
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- 1x SOIC-14 package: U1+C1
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- 2x SOT23-5 pachgae: U2+C2, U3+C3
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- 2x SOT-353 package: U3+C3, U5+C5
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only populate one of the options, depending on the availability of the NOR gate part.
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note: the Cx decoupling capacitor is not really necessary and is just present for good design.
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mode of operation
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=================
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and NOR-gate-based SR-latch is used.
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the RESET button triggers the R signal to reset the latch.
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when a USB cable is plugged, power is provided by the battery to the cable.
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if an integrated circuits is present, current will flow through.
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a 1 k Ohm resistor on the low side (e.g. ground) will create a voltage.
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if the plug draws more than 1.6 mA, the resulting 1.6 V will trigger the S signal to set the latch.
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the BUG LED will indicate the send SR-latch is set.
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the latch remains set until the RESET button is present.
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thus, even if the plug stops drawing power, the LED remains on.
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this minimum 1.6 mA current draw is often caused by the decoupling/bypass capacitor required by integrated circuit, or accompanying voltage regulator.
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when charging, the capacitor acts as a short for a small time, allowing current to flow.
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on USB plugs with just resistors, or LEDs, the resulting current flow is not large enough.
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the TEST circuit simulates an integrated circuit by putting a 100 nF capacitor across the USB receptacle.
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because of the 1 k Ohm inline resistor, and limited 3.3 V provided by the battery, a maximum of 3.3 mA can be drawn by the USB plug.
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this is often not enough to power up integrated circuit properly, particularly if they use a radio interface.
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thus it is safe to use the USB bug detector on bugs, without activating it.
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requirements
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requirements
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============
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============
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@ -91,6 +149,3 @@ to export gerber files for PCB manufacturer (and photo preview + overview docume
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rake fabrication
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rake fabrication
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~~~
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~~~
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fabrication
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===========
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