About this project Introduction In some situations using Arduino and microcontrollers, it is necessary to use a shift register such as the 74HC to directly trigger LEDs, LED arrays or displays, but if you check the datasheet, you will see that you need to be careful with the maximum current in each output and also with the total current so as not to damage any device. Shift Register triggers LED display 1 74HC - Shift Register serial-in to parallel-out According to the datasheet of 74HC, this component contain an 8-bit, serial-in, parallel-out that feeds an 8-bit D-type storage register. This device is very popular for applications on LED arrays, for example, but my intention here is to just discuss your power consumption limit and not all of its functionality. The maximum current allowed per port is 6mA at 5V. Due to these technical limitations it is necessary to apply other interface components to have a more robust and reliable design, protecting the components. There are many applications for it, such as solenoids, relays, LED display drivers, and light bulbs, as well as inductive loads such as small motors.
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The maximum for each port is 8. Within these conditions if you apply one LED for each output port, probably you will go beyond these limits. In this case, a standard red LED has a consumption of 10 mA what means 80 mA at total when 8 of them are used simultaneouslly in your project.
Sure you can put a resistor to limit in 6 mA but certaily you will not like the result of brightness of each LED. Ok, now you are thinking already had seen dozen of projects including books that just use the shift register to drive directely some component. I confess I did this too in another situations just to keep a more compact design, with less components and with lower costs. Maybe they survive due low duty cicle. But with an equipment you must keep working during all day long for a long time, I am not sure whether it will be robust and reliable enough in terms of its time life.
For these conditions you need to use some interface device that can work with larger currents as we will see in next steps.
UDN2981 vs TLC59213
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