Room Management System – Adding a power supply

Now, everybody who has been following the tutorial up to here might have noticed, that I had a couple of typing mistakes and a bug coming in with copy and paste from my working sample. Again, my apologies. The complete code in the last post is complete bug free and I also updated the original posts. However, if you still have a problem getting it to work, please feel free to leave a message and I try to help sorting it out.

Before I proceed a couple of warnings:

Do never attempt to connect a unregulated or AC power supply or anything above 12V to the Arduino board.

Do never attempt to connect a unregulated or AC power supply or anything above 5 V direct to a Atmega chip, the coils of the used relays in this examples, or any other electronic part of the described circuits.

Failing on the above will destroy your Arduino board and any of the used components.

Since we came that far, we would like to try if it works. The first thing we need is a power supply.

If we keep the Arduino board, we can plug any stabilised DC voltage between 7.5 and 12 Volt in. Even with all relays activated I measured never over 1.5 A of current draw, I still suggest a 2A or above rated power supply unit.

The next consideration is the total current draw on the Arduino board itself. With all this LED's and 16 relays, we are above the limits. It is possible to split the supply in to the Arduino board off and run it through a couple of L7805 voltage regulators (1 for 8 relays). That limits the input voltage to 7.5 Volts. Anything above leeds to extensive heat problems on the voltage regulators even if they are mounted on a heatsink.

I personally opted for taking the Atmega chip of and run it together with the rest of the circuit of a PCB and use a 2 A rated, stabilised 5V DC power supply which solves all the rating problems.

The third option would be a voltage regulator circuit with an additional output if the supply for some reason has to be 7.5 Volts or the use of higher rated Voltage regulators if you are bound to use a 12 Volt supply.

In the 2 examples above I used 7805 voltage regulators, 100 uF capacitors in the supply circuit and 10 uF capacitors in the 5 V output circuit. The optional 330 ohm resistor and the LED is just nice to have as indicator that the single circuits are working.

Happy testing