Double 7 segment display with serial control

Design of a 7-segment SMD display, with serial control. With this circuit you can stack as many digits in series as necessary, because the number of control pins doesn't change. In this circuit, the TPIC6B595 is a Shift Register, and a 74HC04 (6 inverters) is used as the 'driver / separator' of the control signals: Clock, Strobe and Enable. When using a shift register, the control signals (Clock, Strobe and Enable) are the same for all digits, and the Data line is connected to the first digit ... chaining the data output of one digit with the next.


The design of this 7 segment display is modular, and you can connect as many digits in series as necessary. Each digit has its own 5V voltage regulator, but it is only necessary to install one to power the entire series. The connections of the output of a module are connected to the input of the next module, thus allowing to feed all the modules with a single voltage regulator. In order to avoid an excessive load of the control signals (Clock, Strobe and Enable) and to avoid possible interferences in the wiring, each module has a circuit that performs the functions of 'regenerator' of the signal.

The integrated circuit 74HC04 has 6 inverters, and they are used in pairs, in order to obtain the same logic level of the input like output. The only detail to consider is that the connection of the 3 control signals with the shift register (TPIC6B595) are made at the outputs of the first inverter. In this way, the CPU should deliver the 3 control signals: Clock, Strobe and Enable in inverted mode.

PWM brightness control (Pulse-Width Modulation)

The brightness control of the set of modules that make up the display is done by the management of the ENABLE signal. By modifying the pulse width of a frequency signal >20 Hz, in order to avoid flicker, the brightness level of the display can be adjusted.


List of components with all kind of details to build a Clock-Chronometer-Thermometer, you can see them on my Web page:


...sorry, but it's in Spanish

Dec 09,2017
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