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I am trying to convert an old webcam from an Asus laptop into an USB webcam

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How do i match the cables from the webcam to a standard black-red-green-white USB cable? Webcam part no. is APCB1317B2, 11P2SF107, CK77 94V-0

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    \$\begingroup\$ Do you want an answer which tells you which colour is which (impossible based on pictures) or an answer which teaches enough topics so you can go through the procedure yourself (which also may not be possible if you don't have the tools)? \$\endgroup\$
    – Justme
    Commented May 2, 2023 at 20:04
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    \$\begingroup\$ The twisted cable is probably USB data. You can figure out which are power/ground using a multimeter. Since it says 3.3V, you may need to add a 3.3V regulator or power supply as well. \$\endgroup\$ Commented May 2, 2023 at 20:14
  • \$\begingroup\$ Is the ASUS webcam definitely just USB? It says USB on it, but it also says 3.3V, and USB is 5V. Maybe it means the protocol is USB, but it needs 3.3V, in which case you will need to convert the voltage \$\endgroup\$
    – BeB00
    Commented May 2, 2023 at 20:14
  • \$\begingroup\$ @Justme I would be interested in learning a but about the topics so that I could do this by myself. \$\endgroup\$
    – Johannes
    Commented May 2, 2023 at 21:15
  • \$\begingroup\$ @BeB00 Ok, but how do I convert the voltage? \$\endgroup\$
    – Johannes
    Commented May 2, 2023 at 21:17

2 Answers 2

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The camera wire harness has 5 wires: 3 single conductors, and 1 twisted pair (pair = 2 wires).

Given the distance from the motherboard to the webcam above the screen, you are lucky and the camera doesn't use HSIC (high-speed inter-chip) USB interconnect that may be found between peripherals that are closer together inside a laptop. HSIC uses different signaling, called DDR2, compared to external USB NRZI. NRZI is used for external connections through potentially long cables, while DDR2 works at the circuit board level. The two require custom digital logic to translate between, they can't be directly interconnected.

The webcam camera wire harness needs to have:

  • a ground wire,
  • a supply voltage wire (presumably 3.3V),
  • a data pair.

There's one extra wire whose purpose we don't know.

Since the wires aren't labeled, we have to determine their purpose. You'll need a multimeter with continuity function ("beeper") or an ohms function to measure continuity between wires and the test points marked on the picture below.

enter image description here

The wire that is connected ("beeps") to the large copper area marked GND is the ground wire. It should go to the black GND wire in a typical USB cable.

The wire that is connected to the test point marked "VCC?" should be the supply voltage wire. Presumably it's 3.3V and would be connected via an LDO (low-dropout) 3.3V voltage regulator to the red (5V) line on a USB cable.

The two wires that are twisted together are the data pair and they go to the green/white data wires in a USB cable. We don't know their polarity, so we'll have to determine that.

First, the camera will have to be powered. You can use two AA batteries for that - it should work OK from 3V. Then we'll have to determine which data wire is D+ (aka DP) vs D- (aka DM). You'll need to set up a circuit as shown:

schematic

simulate this circuit – Schematic created using CircuitLab

The two (at the moment) unknown data pair wires have to be connected via 15k pull-down resistors to the 0V/GND supply terminal. VCC? goes to +3V.

Since the camera is a high-speed device, it will have an internal 1.5k pull-up resistor to 3.3V. This is often not a discrete resistor, but is built into the device, and may only be active when the device is supplied with power. So I wouldn't try just measuring it using an ohmmeter.

Instead, we shall measure the effect of the resistor R1. It's meant to pull the DP/D+ line to a high logic state, overpowering the external pull-down resistor R2 or R3.

So, when things are connected as above, you should measure a voltage close to 3V on one line in the twisted pair, and a voltage close to 0V on another line in the twisted pair. The voltmeter connections are shown too - you'll of course only need to measure one thing at a time.

Once that's done, you'll know which of the two wires in the twisted data pair is DP, and which one is DM.

  • DP should go to a white wire in a typical USB cable.
  • DM should go the green wire in a typical USB cable.

There will be one - fifth - wire whose purpose we don't know. It likely can be left open.

What you should find out/confirm is as follows:

  • gray wire: GND
  • pink wire: unknown
  • brown+white twisted pair: data (DP and DM, to be determined which is which)
  • green wire: VCC?

You cannot use an LM317-based regulator to get from 5V down to 3.3V, since those regulators need about 3V minimum difference between their input and output.

What I would suggest for voltage "regulation" instead would be very simple: two 1N400x diodes in series. Those can be 1N4001, 1N4002, 1N4003, ..., 1N4007. They will drop about 1.5V..1.8V, and the camera will run from about 3.0V-3.4V, and that'll be acceptable in most cases.

So, the final circuit should look something like:

schematic

simulate this circuit

Nothing bad will happen if you interchange the DP and DM wires - the webcam just won't work, but it won't be damaged.

So, if you feel adventurous, just try connecting things both ways, and see which of the two works :)

Good luck - and understand that there's a slight chance the camera will be damaged while doing this. Such is life.

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    \$\begingroup\$ At a guess, the fifth wire might be for the LED that accompanies most of these laptop cameras. It may just connect the anode to an external driver instead of having a command to turn it on or off over USB. \$\endgroup\$
    – Hearth
    Commented May 5, 2023 at 21:39
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There is no way to match those cables directly.

The camera reads 3.3V so it connects to an internal non-standard USB connector which provides 3.3V power supply for the camera.

Standard USB connectors/cables provide 5V.

OK so you can use a regulator to convert 5V to 3.3V. But we don't have a clue how much current the camera consumes so we don't know which regulator is suitable.

You can buy a multimeter and trace the signals which goes where. USB has a standard colouring code for wires but you can't be sure if your cable uses standard or non-standard colour codes unless you trace out which wire goes to which pin on the connector to know the signal names for the red/black/white/green wires.

Then you look at the photo where there are 4 testpoints likely for the USB interface. One is for big ground plane. One is medium track width for 3.3V power. Two small wires paired for data that go to camera IC. Look up which wire colours they connect to. You don't know which data wire is which, but it won't damage if data pairs are swapped.

Now, armed with a regulator and wiring connected hopefully correctly, don't plug it into your best and most expensive computer as it may instantly turn into a dead brick if you did not connect the wires correctly. People really do want to do weird stuff and plug them into their computers and don't understand the risk of damage. Just for example, if you did damage your computer, it costs way more to fix or buy a new one, than to simply buy a decent webcam which is likely better than anything salvaged from an old laptop.

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  • \$\begingroup\$ Ok. But is there something like a device that can still make it work? Like a device that converts the voltage in some way? \$\endgroup\$
    – Johannes
    Commented May 2, 2023 at 21:19
  • \$\begingroup\$ @JohannesFerenius the part you're looking for is called a voltage regulator. A very common part with many different varieties \$\endgroup\$ Commented May 2, 2023 at 21:28
  • \$\begingroup\$ @user253751 Alright, just wondering if they are complicated to use or if you think that someone like me with little to no experience could figure it out? \$\endgroup\$
    – Johannes
    Commented May 2, 2023 at 21:40
  • \$\begingroup\$ @JohannesFerenius look for a 3.3V linear or LDO regulator, super simple, one connection is input, one connection is output, one connection is ground. Just make sure that 5V input is okay, because some of them want to have quite higher input voltages (LDO specifically means that it doesn't need a high input voltage). Depending how much power the camera needs to use, it could get a bit warm or even hot, so you might choose one with a metal screw hole to attach a heat sink, just in case you need one. \$\endgroup\$ Commented May 2, 2023 at 21:43
  • \$\begingroup\$ @user253751 Ok, thanks! But when you mean hot, do you mean the camera or the voltage regulator? \$\endgroup\$
    – Johannes
    Commented May 2, 2023 at 21:47

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