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README.md
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README.md
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the USB bug detector identifies USB type-A cables (or devices) with integrated circuits.
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The USB bug detector identifies USB type-A cables (or devices) with integrated circuits.
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<img src="picture/v1_front.webp" title="front" height="250"/>
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<img src="picture/v1_back.webp" title="back" height="250"/>
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@ -6,7 +6,7 @@ the USB bug detector identifies USB type-A cables (or devices) with integrated c
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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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To use the USB bug detector, follow the steps provided on the back of the board:
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- insert a CR1220 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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@ -15,37 +15,37 @@ to use the USB bug detector, follow the steps provided on the back of the board:
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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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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 SIMULATE 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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To ensure that the USB bug detector works, after pressing on the RESET button, press on the SIMULATE 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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when the LED is on, the USB bug detector draws 3 mA.
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when the LED is off, the USB bug detector draws 64 nA.
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this results in a idle battery life of 62 years (for a typical 35 mAh CR1220 battery).
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this is on par with the self life of the battery (~ 1%/year).
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When the LED is on, the USB bug detector draws 3 mA.
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When the LED is off, the USB bug detector draws 64 nA.
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This results in a idle battery life of 62 years (for a typical 35 mAh CR1220 battery).
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This is on par with the self life of the battery (~ 1%/year).
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mode of operation
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=================
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an 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 when the 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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An 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 kOhm 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 when the 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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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 SIMULATE circuit simulates an integrated circuit by putting a 100 nF capacitor across the USB receptacle.
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The SIMULATE circuit simulates an integrated circuit by putting a 100 nF capacitor across the USB receptacle.
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because of the 1 kOhm 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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Because of the 1 kOhm 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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