Agree, very useful when on the dashboard of your car is digital electronic watch, with its highly visible contrast display with clear digits that did not irritate vision, in harmony with the design of the instrument the panels.
Unfortunately, to find in the trade network of automobile clock corresponding to such the requirements are almost impossible. All we "schedro" trade offers - Chinese "consumer goods" to "blind" LCD indicators. Else to purchase quite expensive, so-called "trip computer", domestic production, with display on the LEDs, and use it as a clock.
But this is not the way - except for unreasonably high prices, led indicators such devices are difficult to read during the day, and the design leaves much to be desired.
In my opinion, the best option for car is a watch with vacuum fluorescent indicator type "ICU". Indications of such an indicator is equally clearly visible both day and night, with excellent clarity and a pleasant the blue-green color. In the electronic literature from the 80's and until recently, there are many descriptions of the watches on these indicators performed on BIS KIK, KAHL, CREW. But the use in the car these are very good and the time-tested schemes prevents too high a voltage (not below 24 V) necessary for the operation of fluorescent indicator. Of course, the ventilation may to work with the litany of 12, but its benefits will be lost.
In the car I set the clock on KIK and ILL-7/3, made by the model scheme, and used the power voltage source 28 In on-chip DC-DC Converter MC34Q63A.
The Converter is implemented in the model scheme enable to improve MSA voltage (Step-Up). The voltage of the car battery is supplied to conclusion A. Through a resistor R1 to the output stage pump inductance L1 In the chip has a generator with an output key transistor.
The emitter of this transistor is output on pin 2, the collector - to pin 1.
In this circuit, the emitter is connected to negative (pin 2) and the collector loaded to the inductance L1. The pulse frequency is about 100 kHz. L1 appears EMF of self-induction, the value of impulses which significantly exceeds the supply voltage. This AC voltage is rectified by the diode VD1 and C3 a constant voltage.
To stabilize the output voltage is used comparator input A1 - conclusion 5. The voltage across it must be a 1.25 V. If the voltage is different from this value is a change of the parameters of the pulses at the collector the output transistor so as to compensate for the change.
The output voltage may be higher - up to 40 In, its value depends on the ratio of the resistances of the divider R4-R3. Coil L1 contains 35 turns sew 0,35 on a ferrite ring CHH.
When the output voltage of 28 V maximum output current of 100mA. Filament goal ALV-indicator shall be supplied directly from the car battery (through the quenching resistor or by a variable-voltage generator, as it is proposed in the model scheme CIC).
Author: P. A. Krivenko