Auto watch with improvements

Some cars do not have properly installed clocks, thermometers, etc. indicators. Of course, it is quite possible to do without them, but useful information is always pleasing to the eye.
So, the VST-7009V auto-watch - they have not yet been reviewed and broken here.
Show the current time, the temperature in the cabin and overboard, the voltage of the onboard network. There is a built-in battery and an alarm clock in addition.
The clock came in a small slightly wrinkled box.

The watch itself is tightly crammed into a box in a little bubble,power cable to the cigarette lighter, external temperature sensor, double-sided tape circle, instructions in Chinese, English and Russian.

The case is plastic black with a blue insert edging. The dimensions of the watch without a foot are 94 x 56 x 27mm. The foot allows you to slightly adjust the position of the watch

Behind the lid are two LR44 watch batteries.
The current consumption of hours in the absence of external power - 14 μA

General view of the work

Self-adhesive external temperature sensor, cable length 2m.

Connection through the cigarette lighter, cable length 1.5m, no protective fuse in the plug.

Both wires are connected via connectors in accordance with the color. You can not mix up the connectors - the watch will burn out instantly.
The display backlight turned out to be orange for some reason /blue instead of the expected green. The backlight color is switched at the back of the watch via a switch. The orange color is unpleasant and annoying, the blue color is slightly better, but still not very ... My eye is more pleasant with green or white.
I had to open a dispute with the seller to compensate for the non-compliance (I won half the cost).
The photo shows how the clock will show during the day.

And at dusk

In the absence of on-board power, the watch is powered bybuilt-in batteries, the backlight is naturally turned off. Without backlight, the display is poorly read. There is no additional protective glass in front of the screen.
Pressing the buttons is confirmed by a peak.
Assignment of control buttons
TIME - Time - month - date display, switching the time display mode 12-24h, setting time, month, date, year.
ALM - Displays the time to set the alarm, correction of the time to set the alarm.
SNZ - Setting the Sonya function for an alarm
UP - Turn on - turn off the alarm; during setup, increases the value.
DOWN - Switching the temperature display mode Degree - Fahrenheit, the inclusion of ice warning, when setting decreases the value.
In the range of outdoor temperature from -1 to + 3g, the clock starts to pick, apparently warning about ice on the road. To keep them silent, you need to press the SNZ button.
The readings of the internal sensor by 1g overstate the actual temperature (most likely due to heating by the circuit). The outdoor sensor seems correct.
Voltage is normal, but readings are ± 0.1V
To comply with tradition, the watch was disassembled.
The halves are fastened with one small self-tapping screw + latches.

Nothing unusual was found inside - an ordinary Chinese-made watch.
Mounting in C grade, the board from the flux is not washed.
The design of a typical desktop clock, the components are not fixed and will probably fall off from vibration over time. It is very desirable to fix them with a neutral sealant.
The indicator connects to the board with a ribbon cable with graphite tracks, which is also undesirable for auto watches.
If necessary, the fixing leg can be easily unscrewed.

Real watch

There is a 3.3V voltage regulator.
An internal temperature sensor is installed on the board (10kΩ thermistor).
Why is there an alarm in the auto-clock - it’s not clear ...
True, the alarm did not work for me, because the sound emitter was in a cliff, I had to solder the sound emitter.
Backlight organized by a two-color LEDrectangular section, which is inserted into a special niche diffuser. Thoughts about replacing the LED were scattered - such an LED of the right colors could not be found ...
The manufacturer claims the possibility of working on a voltage of 8-30V, but I would not recommend using them on a 24V car, because The HT7133 can be overloaded with voltage and power dissipation.
The operational amplifier is used as a voltage comparator, on which the simplest integrating ADC is organized.
The watch was slightly modified to increase its survivability and convenience.
1. I plugged into the plug a small 2 Ohm resistor as a fuse.
2. Secured with a neutral sealant everything. that may fall off the vibration.
3. Replaced wiring connecting to the batteries on the way.

4. Made an automatic adjustment of the brightness of the display backlight. The fact is that at night the bright illumination of the watch is a little distracting, so I wanted to automatically reduce its level.
The scheme for finalizing the backlight unit.

The brightness control works as follows:
- While it is dark or twilight - the photodiode and transistor are locked and the brightness of the backlight is determined by the resistor of the initial backlight current (about 1mA). The indicator is dimly lit, but well read.
- As the illumination increases, the photodiode currentincreases and the transistor gradually unlocks, the current through the backlight LED increases up to 25mA. The current change coefficient is about 25, but by eye the brightness changes every 5 times, which is quite enough.
- In bright sun, the transistor is fully open, the maximum current is 25mA. The current through the photodiode does not exceed 1 mA.
The photodiode took an IR with side reception from the receiver of the remote control commands of the old domestic TV.
I don’t remember his type anymore, but many of the visible and infrared ranges are suitable (they also see sunlight well)

I installed it like this - I drilled a case with a thin drill under both terminals, inserted it, bent the legs and glued it with epoxy glue on both sides.

At the same time, the photodiode sticks out, but does not go beyond the dimensions of the watch and looks like a microantenna. The direction of the sensitive side is pre-selected depending on the location of the clock.

Refinement on the print side. Resistors 20R and 47R are removed, a diode is installed instead of a resistor 47R (to equalize the voltage of the lights) and a backlight resistor 100R

Refinement by the elements. Added jumper and P-N-P transistor SS8550 (you can put any similar).

After soldering, the transistor is also fixed with a sealant.

The main difficulty in the process of remaking is not to break the ribbon cable to the indicator, it is too weak ...
After assembly, the watch looks like this

There is no photo of the clock installed in place yet, as I put it - I will add it to the review.
There will be questions - ask
p.s. I tried to mix both colors, it turns out like this:

p.p.s The audio signal still repaired
Conclusion: the watch is of mediocre quality, it will not last long in a car without modification.