LED display control

    For microcontrollers with a small number of input / output ports, typical parallel control schemes for multi-digit 7-segment LED displays are completely unacceptable. Remote displays in a multi-channel system "eat up" almost all the input / output resources of the microcontroller even when using serial data transfer. Although there are specialized microcircuits oriented to similar tasks (such as MAX7219 / MAX7221), but two-digit indication with their use is “money down the drain”.

    Below is a simple technical solution to the problem. To control the indicator segments, a shift register is used, and the choice of familiarity is made through the data line of the interface. The software component, in this case, is no more voluminous than the known methods.
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    Two transistor switches connected in series and controlled by the SD interface line form antiphase signals. After loading the shift register with the refresh rate of the display data, the log level is set on the SD line. 0 or log. 1 to indicate the appropriate familiarity (Fig. 2). The CLK signal line of the interface can be used with the same success, however, the proposed option is more convenient for software implementation of group control of displays with a common CLK line. The length of the control interface can reach tens of meters, and twisted pair ensures reliable transmission. Very convenient are the local power sources of the display module of the type “charger for sotik”. It is less efficient, but also easy to control 2N-bit displays (Fig. 3).

    Work logic

    The control algorithm is simple. When the data update moment arrives, the state of the SD line is analyzed and the data source (s) (low or high bits) are selected, the serial transmission subroutine is called and, upon completion, the current state of the SD port is inverted. It is not much more difficult to output a three-digit number with a comma (temperature) to a two-digit indicator.

    For example, a circuit diagram of a module is provided, which additionally has an optothyristor control channel.

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    Options

    When using high brightness indicators, transistor switches are not needed.

    Practical use

    An indication module with the described control method is applicable for modding the computer system unit to display processor load and temperature inside the case.

    PS Please do not kick, the first time I publish an article
    PSS The author of this invention is my father. Those. I act as a link between him and the global web.

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