At the bottom, centre is the mini USB socket where 5v DC is drawn. Initially, the transmitter uses a 6.8 ohm resistor, and then two diodes to drop the voltage from 5 to 3.8 volts and provide inverse polarity protection.
The diodes are seen as a pair of dark rectangles just below the LED. These have a forward voltage drop of around 0.6v each to reduce the voltage to a theoretical voltage of around 3.8v.
The positive terminal of the battery goes via the smaller electrolytic you see at the top then through what looks like a resistor but (top left) but is really an inductor forming a switch mode supply.
Next to it, there's a switching transistor. The transistor chops then the device is in transmit mode. A square wave can be seen on the top pin.
The markings on the device read 2101A 0616/33. I am unable to identify this device.
Current Drawn at 13.8V (no batteries fitted)
| Adaptor | Quiescent current | Standby Mode | TX Mode | ||
| BL Off | BL On | BL Off | BL On | ||
| Ugly White | 9 | 10 | 27 | 39 | 61 |
| Posh black | 17 | 18 | 35 | 47 | 69 |
If included, the 12v to 5v cigar lighter power regulator can vary between
suppliers. Both of these ChauYu devices has a red LED but the quiescent current
is quite different between the two.
The simple voltage adaptor contains nothing more than a ceramic
capacitor, LED and 78L05 regulator IC. There are also a couple of 270Ω
resistors. These are both in series with the LED to provide current limiting.
The LED is fed from the low voltage / regulated side of the regulator, i.e. at
5V.
The PCB, interestingly enough, is sparsely occupied but
includes placings for a whole lot more components, including an 8 pin DIL chip.
There's sign of an inductance after the chip on this board so this is possibly a
layout for a switch mode supply which was decided against.
The board bears the words 'Martking Electronic'