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Wednesday, January 30, 2019

Car DVR replacement and related shenanigans - part 2

Moving along with more details, like I mentioned in the previous post, the rear camera was reused from the previous installation. This CCD based camera happens to be superior to the basic CMOS camera bundled with the kit. Both in terms of the quality of the sensor itself and its low light sensitivity, but also regarding the lens, featuring a wider viewing angle (important given its role as a backup camera).

The only change however was a substantial improvement in the mounting design, by having added an U-shaped plate in the rear of the camera, with a 4-screw mount instead of the original 2 screws attached to the sides of the camera. This provides a more solid attachment to the L-shaped aluminium parts that in turn stick to the door through an adhesive:

The existing wiring was used. I also learned that the pinout of the miniature 4 pin connector is the same in both the new and old car DVR units. The cabling goes in through the rear door and through the roof:

in order to reach the compartment near the rearview mirror, where the connectors and cabling meet:

To function properly, similarly to a car stereo, the mirror requires two power rails:

  • ACC - the accessories power source. This rail is only powered while the car key is turned on;
  • B+ - permanent power from the batery. This pin serves to keep the mirror in standby mode, and to prevent the sudden power switching (when the car key is removed from the ignition) from causing data loss or microSD card corruption.
I could easily obtain power in these conditions by selecting the appropriate unpopulated slots in the 

fuse box underneath the steering wheel:

For the B+ power, I selected one of the slots (F39) between the two square high amperage fuses. For the ACC I used another empty slot, which would serve for the heated seats fuses (which my car is not equipped with). Given that the heated seats are only active if the key is turned on, this would be a good point to tap the ACC rail.

Before these terminals that connect to the fuse box, each cable has a 3 Amp fuse, in order to protect each of the rails.

The sketch below depicts the connections and the circuit that is present between the DVR input connector (an 8 pin miniature round connector) and the rectangular 8 terminal connector. The reversing light signal filter is represented, and the camera voltage switching relay as well:

As explained in the previous post, the later serves the purpose of switching the 12 Volts required for the rear camera, through the 5 Volts signal that the DVR is capable of providing (which were enough for the original camera, but not for this one).

The mirror is reasonable discrete, with its conventional design. In operation it is a very useful gadget to have in the car. For example in slow traffic it helps define the expectations for the duration of the journey with the help of Waze:

In general it is a feature rich package, where features such as forward vehicle movement detection are quite useful during the slow traffic, to avoid impacting traffic with the distractions, and lane departure detection, which provides an extra degree of safety, when driver fatigue is a concern.

With the GPS antenna mounted in the vehicle (inside the dashboard), the device is quick to obtain a fix, and the number of locked satellites hardly ever drops below 8. The device is also capable of picking up the chinese satellite constellation, but normally there are few of these satellites in line of sight ( 2 at most, from what I could observe).

Another feature that the mirror was advertised as having, is a hardware police radar detector. In the ecommerce sites where the mirror is for sale, the existence of an app (only in chinese) is advertised. Given that this app was not preinstalled in the device, I asked the seller if he could provide a link to the app. Soon they replied with a link to an apk file with the name "YuanDogRadar 2.6.11". I installed it and it corresponded to the app the presented in the product screenshots:

There is virtually no more information that I could find about this app, other than this screen. It is unclear if there is indeed a hardware detector, and if so, which bands it can detect.

It is worth noting that in the settings screen there is a serial port setting (/dev/ttyMT1). It is unclear however if this is for the hardware detector (if it exists at all), or if it is for the GPS serial port (most apps don'r require the user to provide this info though).

In my testing I have only left the app running, during a test drive. There is a chinese female voice that talks frequently (which I understand 0 % of), and occasionally the application beeps while I am driving the car. It never beeped while passing by the known fixed radar spots. In the center, a dial displays the GPS speed.