Key chain camera (Hetai HD-818)

Camera teardown

Dedicated car charger teardown

Emergency charger teardown

Related: My USB adapters, USB Mini connectors, #11 Camera on ChuckLohr's 808 Car Keys Micro Camera Review, The REAL (#11) HD Key Cam Thread on RC, especially post #3294

Key chain camera (Hetai HD-818)

Small and cheap (about $40 with accessories) bulk key chain camera is available from several dealers on Ebay. I got my one from Eletoponline365 as Car key chain HD DV DVR Video Driving Recorder 720P in a pack with car charger and emergency charger. It exists in many variants. The one I have is also referred as Hetai HD-818, HD720 or just as a 808 camera #11, PCB revision #2. Other versions have a different hardware. Camera #11 provides video superior to the all previous models. It uses Novatek NT96632BG chip and H264 codec, which helps to improve bit rates.

Camera teardown

It is easy to open it. There are only two screws outside and two inside. But it was hard to cut hot glue. (Warning: The battery is powered until you desolder one of battery terminals. Any use of heat as well as short circuit caused by any metallic surface may easily cause semiconductors damage!)

As you can see, my camera came with a camera circuid mounted crooked. One was surprised that it snaps something different that I intended.

camera teardown top side PCB view
top PCB view bottom PCB view

Revisions #1 and #2 of this camera have very ugly “charging” circuit. In fact, dedicated car charger USB pin #4 is connected to the plus terminal of the Li-Pol battery pack. It means, that the dedicated car “charger” does not charge the battery, but it only “invisibly” powers your camera (camera electronics is not aware of the external charger and does not switch to the USB mass storage or web camera modes). Yes, is is an ugly trick, where your battery gets constant voltage about 4.05V from outside. When discharged, it may provide initial charge. When your camera is fully charged before going to connect this charger and record car ride, yout camera first depletes the battery. When voltage reaches 4.05V, energy starts to flow from the car “charger”.

Dedicated car charger teardown

car charger teardownThe dedicated car charger looks like one of the standard Mini USB car charger 5V/1.5A, but it is not true. The charger has a different pinout (uses pin 4 for Vcc instead of pin 1). My one also has a different voltage – only 4.20V. This is a bit strange, because the label cleanly says 5V 1.5A.

In the first moment I thought that it is failure of my charger. But after opening it, I believe that it is not a faulty charger, but an intention.

car charger PCB connection side detail of U1
car charger PCB parts side upper view car charger PCB parts side lower view

If you look at these photos in detail, you can see that there was originally present a different R3 resistor. It was cut out (relics of its wires are still present) and a different resistor was soldered on the bottom part of the PCB. Guessing that the charger comes as a semifinished product from its manufacturer and the camera manufacturer finishes that car chargers specifically for this camera.

detail of R2 detail of R3

The charger uses a switching power supply IC MC34063L which seems to be equal to MC34063. Looking at the resistors color codes and the IC data sheet, the charger designated voltage does not seem to be 5V, but only

Vout1 = 1.25 × (1 + R3/R2) = 1.25 × (1 + 25k/10k) = 4.375V

As the real voltage is 4.19V, I am guessing that the Schottky diode is connected on the output and causes its typical voltage drop (~0.18V).

Vout = Vout1 − 0.18V = 4.195V

Summary: Car changer not only uses a non standard pinout, but it is also designated to produce a non-standard voltage 4.195V!

Emergency charger teardown

Emergency AA-battery charger is provided with a dedicated USB pin 4 cable. It seems to be a simple two transistor LC oscillator step-up. There is no regulator and the output voltage varies in a wide range between about 4V and 5.664V (powered with a single 1.5V battery; with the 1.2V NiMh accu battery, the upper voltage is 5.624V). When shorted, it provides 0.28A. It is always on, LED indicates presence of the output power consumption. Idle power consumption is about 95µA, a battery kept permanently inside should last at least 1 year.

AA charger teardown AA charger PCB bottom view
AA charger top view 1 AA charger top view 2
AA charger top view 3 AA charger top view 4