If my car gets in the way

The conversation was something like this.

Sanya: “I bought Chinese indicators, I dream of assembling the device so that the phone number glows for the car. But I don’t know how to connect them. Somehow we need a microcontroller. ”

As a programmer, Sanya did not know what was needed not for the microcontroller. In any case, not directly. But I liked the idea. Simple, cheap, does not take much time and usefully. I wanted to participate. And so began our small project.

Let's start with the result.



Although the project is not intricate, but the project. Shared with Sanya responsibilities: I - iron, he - the program. We made a plan.

1. Analogs
2. Circuitry
3. Constructive
4. Equipment
5. Program
6. Assembly
7. Test

Is it worth it to make such a device? I came across several analogues, but all were without digital indicators and with the ability to set the number once. The most interesting device turned out to be with static illumination of the installed number. Cheap and reliable. But the fantasy spoiled by the present could not stop there. Nevertheless, we decided to do our own thing.

The block diagram of the device is shown in the figure. As you can see, everything needed six registers 74HC595D, microcontroller STM32F030, indicators and a button. TP4056 battery charge module purchased. Of course, there is still a small wiring in the form of resistors for current protection and capacitors.



I made the board as small as possible, two-sided and with the installation of components under seven-segment indicators. And you can do even less by installing the registers in the SOIC16 package, but the latter are somewhat more expensive.

The study of the corps took the most time. Fortunately, the modest CAD skills allowed me to outline a “simple and concise” construct, which may not pretend to be the design of the year, but can cope with its function.



All equipment, from indicators and ending with screws for mounting a printed circuit board, was ordered in China. Although with a significant delay, but in full, the comrades from the heavens provided us with everything we needed.

The program, as agreed, was written by Sanya. From the functional: enter, change, save the number; brightness adjustment, and put into sleep mode. The plans include a list of "favorite numbers", a mode of periodic increase in brightness for sunny days, there are thoughts on the indication of charge.

Of course, the operating time of the device without recharging directly depends on the brightness of the indicators. At maximum brightness, the device consumes up to 100 mA, the battery lasts a maximum of 8 hours. However, reducing the brightness can drop below 20 mA! In this case, the number will still be quite clearly visible. At “medium” brightness, as in the photo, the device worked for two days, while charging takes 2 hours. The Chinese module reports the end of the charge. Decent result.

And what about the cost. Everything is not so rosy here. The total amount amounted to 575 rubles and one penny. Given that the red price of such a device is 500 rubles, the prospects for its production and sale seem vague. But maybe not everything is so bad? Maybe. The case was printed on a 3D printer and it cost 230 rubles, but the battery is 136, and the printed circuit board is 104. So there is room to save.

The last item in our plan is testing. There are comments, for example: the case does not fit well (about print quality), the battery holder did not fit (error with dimensions), during sleep, the device consumes 1 mA (remark on the circuit).

One way or another, the two devices we have assembled are admiring on the panel by the windshield.

Me: "Well, so, Sanya, your dream has come true?"
Sanya: "Yeah."
Me: “Then let's adjust the brightness with a PWM, and I also want navigation, and also so that the dots run when charging ...”