This question is a follow-up to my previous question about controlling a ceiling fan with a Raspberry Pi. I have decided to use an Arduino Nano instead of a Raspberry Pi.

After some closer investigation, I have realized that my fan controller uses triacs for both the lamp and the motor. I created a schematic that uses the same basic system as the original controller. My questions are is this triac configuration correct and will my power supply supply the 9-20 volts that the Arduino Nano needs?


Edit 1: After some searching I have lowered C1 from 1000uF to 100uF as it is just a smoothing capacitor.

Edit 2: I have updated the transformer to have two taps. Here is the fully-updated schematic:


  • \$\begingroup\$ Not part of your question, but if you use a full-wave bridge, don't connect the transformer center tap. Or, use only 2 diodes with the center-tap. Can't tell which is best without knowing the transformer voltage. \$\endgroup\$
    – Mattman944
    Commented Dec 8, 2020 at 15:29
  • \$\begingroup\$ @Mattman944 I am planning for the transformer to convert 120V AC mains to 40V AC. I have disconnected the center-tap in edit 2. \$\endgroup\$
    – ImTheSquid
    Commented Dec 8, 2020 at 16:13
  • \$\begingroup\$ @ImTheSquid: 40 VAC from the transformer is much too much - you should aim for 15 - 18 volts at the input to the 7812. \$\endgroup\$ Commented Dec 8, 2020 at 16:36
  • \$\begingroup\$ @PeterBennett Looking at this data sheet 25 to 27 volts in will result in a steady 1A output which is what I want, and anything less than that could give unstable current (correct me if I am reading the sheet wrong). If I did my math correctly after the bridge I should get about 26V DC. \$\endgroup\$
    – ImTheSquid
    Commented Dec 8, 2020 at 16:57
  • \$\begingroup\$ The regulator will produce the desired output voltage for any input above 14.8 volts (second "output voltage" line). The higher the input voltage, the higher the power dissipation in the regulator, and the larger the heatsink you will require, so you want to keep the voltage across the regulator as low as practical. \$\endgroup\$ Commented Dec 8, 2020 at 17:33


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