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How to Build a DIY Fully Automated Light Controlled Fan Regulator

By on July 6, 2015
fan controlled regulator circuit










The Life of an electronics repair engineer is not always about repairing something that is broken. Or about something that needs to be replaced to fix a device. Sometimes it is also about fixing a problem by designing something that still even doesn’t exist. This article is an example of such an enterprise. This project can also be used as a great example how to design something before even building it.

This little project shows in some detail how you can design and also simulate your circuit on your pc before you grab your solder iron. This article explains how to build a DIY “Fully automated Light controlled Fan regulator”.

It all began about 4 years ago when my brother asked me to help him in making a Fully automated Fan for his Toilet. He already had placed the 240V AC Fan in the Ceiling and an electrical power socket next to it on the wall. So that was handy to place my Fan controller in later on. My brother had previously placed a Manual controlled switch in the Fan power cord but wanted to eliminate the need to do it by hand everytime you left the toilet. And even often forgot to switch off the Fan after a while.

So I checked the internet and couldn’t find any suitable working circuit that also was cheap and easy to Build. So I decided to design one myself. I saw some circuits on the internet that used a NE555 ic but they all didn’t work! But I adapted the idea of a NE555 in my circuit because it is easily useable as a fantastic time delayed switch. And they almost cost close to nothing.

I used an older dated version of Tina (v8) which I used to develop and simulate this project. For this circuit probably every Trial version will work.

Because my brothers little Toilet room is rather dark, everyone always uses the Light switch when he visits it. So it only was logical to use an LDR as detector to know if and when the Toilet was occupied or not. And I found an empty Power adapter that I choose to build my Fan controller circuit in to. The open position that used to be for the Voltage Selector was ideal to place the LDR behind. (Of course with a little transparent protection window of some plexiglas in front of it afterwards. To prevent that someone could be able to get in contact with the dangerous 230 V AC if he would try to touch the LDR. And I made sure that it also was not possible to touch any of the other parts in the Adapter). Because it all has to fit in the Adapter case we can’t use a transformer, so we use a special X2 ~250V 0.47uF Capacitor with a 9Volt zener and some diodes and a few extra capacitors.

The two wires (Brown and Green) coming out of the Power adapter are the wires for the already placed FAN. And the 230 VAC Plug in the re-used Power adapter for this project, plugs easily into the Electrical Power Socket on the wall right under the Ceiling were the Fan is placed.

And when the Power adapter was placed, the LDR would look in the direction of the Light Bulb in the Toilet room. Light Bulb on means that the Toilet was occupied and the LDR value would show a Low Resistance value. Only when one would leave the Toilet the Fan should start to turn. There are commercially circuits but they all use one of the Switch wires of the Toilet Light Switch.

My circuit would not need this extra signal wire because it would work Fully Optical. Sort of wireless in a way and therefor simpler and better! No need to reroute the existing wires in your Toilet.

The photo below shows the final product with the LDR looking out of an old Power adapter.

fan controlled regulator

Before I show the final working Circuit I will show all made project photos of the Ready Working Adapter. Keep in mind that the bottom pcb really looks a bit chaotic but that is only because I made my circuit on the original rearranged Power Adapter pcb. And I made another little pcb on top of that, so that it still fitted in the original Power Adapter housing.

Also don’t let the way my project looks in any way make you disapprove of how I built it because it already worked for over 3 years or more now without any problem whatsoever!!

So I am really proud on this result! And I hope that it will convince the reader to try to develop something from scratch also with the help of Programs like Tina. There also is a Tina v.9 Free version ,obtainable on the Internet as a Texas Instruments (TI) version.

fan controlled regulator2

Above: Don’t let Looks deceive you. This could be a commercially designed Project of which this was the Prototype ! (That already works for about 3 years now without any trouble at all!)

fan controlled regulator3

Above: Showing more clearly the special x2 250V Capacitor that replaces using a transformer.

fan controlled regulator4

Above: LDR with NE555 chip in socket and with TRIAC on Alu Cooler. Safety Fuse on other side.

fan controlled regulator5

fan controlled regulator6

Above photo shows the blue potentiometer that adjusts the LDR sensibility.

fan controlled regulator7

Above: View on top mounted PCB that holds the Transistors and the TimeDelay Variable Pot.

The Green Capacitor is a special x2 250VAC Safety Capacitor used to deliver the current for this “Automated Light Controlled Fan Controller”. Do not use anything less to prevent Fire or Short Currents. The max. provided current can easily be calculated out of Xc = 1/(2 x Pi x Freq in Hz x C).

fan controlled regulator8

And Finally here comes the Circuit that is Easily Build and working Great!

schematic for fan controlled regulator

Note: Click on the above schematic to view in larger size.

Here is the list of the components:


Hope you all liked it !








Albert van Bemmelen, The Netherlands.

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  1. Peter O

    July 6, 2015 at 12:18 pm

    Great build obviously but I can't grasp exactly what is switching what.
    How is the "fan run time" controlled/adjusted?
    I have never heard of a safety capacitor which seems a crucial element in this design?
    Similarly I have to guess what an LDR is or go google it.
    Not everyone has the knowledge to assimilate the finer points.

    • Albert

      July 6, 2015 at 3:06 pm

      Hi Peter, It is a Toilet (or Bathroom if you like) Optical controlled FAN switch. When you visit the Toilet and switch On your toilet light Bulb it sees you are there thanks to the LDR (Light Depending Resistor). That is the optical part. And only if you leave the Toilet and switch Off the Light it will turn on a FAN to clear the air. For a Selectable preset Time. And then it Switches Off the Fan automatically. Until the next visitor used the Toilet and leaves again.
      The safety Capacitor is a special X2 version that handles the Line Voltages easily without breaking up dangerously and handles temperatures from 85 degrees Celsius and higher. See this Link for more info:
      Whatever you do NEVER touch the Line Voltage or any component in circuits like my Automated Optical Fan Controller! Only a normal Transformer (No Variac either) would make a safe to touch envirement.
      Hope this explains your questions?

  2. Mark

    July 6, 2015 at 1:02 pm

    Hey Albert,
    Thanks for all the detail & schematics. It's great when you are able to come up with a solution to a problem as you said, rather than just fixing existing items (although that is heaps of fun too)
    Congratulations on your project.

    • Albert

      July 6, 2015 at 3:17 pm

      Hi Mark,

      Thanks for your always positive reply!
      And Big Thanks to Jestine who made something like enlarging of the schematic possible, I didn't know he could do that.

  3. Yogesh Panchal

    July 6, 2015 at 2:43 pm

    Congratulations! for your successful project.
    Another solution for your need is to connect the FAN directly to the Toilet Light switch Single switch for light and FAN !!.

    • Albert

      July 6, 2015 at 6:48 pm

      Hi Yogesh, you describe the old not automated situation. When you could easily forget to switch off the Fan or light bulb. With my circuit the activated time is selectable and the Fan automatically is turned On AFTER you leave the Toilet. And after the preset activate time is reached the Fan also Stops automatically. So you can enjoy doing a Poopoo or a little Pee-pee without being distracted by the Noise of the turning Fan.

  4. Dave.

    July 6, 2015 at 2:58 pm

    Hi Albert, great idea using an LDR. But like Peter not sure if you arranged your fan to run for a certain period after triggered. I see you use the 555 as a timer so there must be some delay. Excellent idea and its good to see innovation.

    • Albert

      July 6, 2015 at 7:19 pm

      Hi Dave, If you look at the schematic you see P2 (4.7M), R2 (47K) and C3 (2200uF). The Potentiometer P2 sets the wanted Monovibrator activate pulse time of the NE555. When the NE555 is activated by T2 and a pulse on pin 2 on TRIG Sets the NE555, Capacitor C3 will get charged until C3, and pin 6 TRES of NE555 reaches about 5.98 Volt. Until that point is reached the Output pin 3 of the NE555 activates the Fan by continuesly triggering the Triac on its gate. But at level 5.98 V reached on C3 the Monovibrator Pulse stops and the Fan will end its activity automatically until a new Set event on pin 2 of NE555 occurs. R2 (47K) protects the circuit from large discharge currents from C3 when P2 is in a low Resistor setting.
      If you want to see it working you have to build it or Simulate it on programs like Proteus or Tina. But the first program I never had used myself before.

  5. Humberto

    July 6, 2015 at 8:16 pm

    Hi Albert, you are 100% right. Not always an electronics repair engineer has to mend broken devices. Design is part of our profession.

    • Albert

      July 7, 2015 at 3:20 pm

      Yes Humberto, I agree and was very glad to be able to help my brother with this great working device.

  6. Robert Calk

    July 7, 2015 at 1:00 am

    Thanks for the article, Albert. A LDR Trip5 timer circuit is not a new thing. It's been around for a long time.
    I don't like transformer-less power supplies that are connected to mains voltage - it's too dangerous.

    • Albert

      July 7, 2015 at 4:26 pm

      Hi Robert,

      Of course there must be thousends of different NE555 circuits. But at the time I made this circuit and Simulated it I could not find ONE single circuit that worked Optical. And even the commercial ones used one of the Switch wires and weren't Optical at all. In fact the capacitor (C5 4.7uF) significantly minimizes this presented circuit and is probably a very, very old Electronics Trick to enable the Triggering the way I needed it here. It is used as a kind of memory cell and makes this circuit very reliable at the same time. And I know you are kind of a 555 Wizard from what I've read on some older Posts. And if you build these kind of small devices without using a transformer there is no real danger if you keep everything in a closed sturdy housing and use the right precausions like fuses and the right safety parts, nothing can happen. I also used 0.2 mm wire for some of the low voltage (9 Volt) circuit connections. So even if something other then the fuse would burn out, it would also be a kind of safe circuit breaker. And most new houses like my brother's have all TWO safety Earth leakage circuit breakers.
      (One for the higher Power washing machine group, and a second for the normal groups. With their different Earth current values).
      But that said it is just as safe as your ‘unsafe’ pc power supply for laptop or desktop that even if it is boxed in a plastic housing, isn’t made for outdoor use!
      (When it gets wet it is lethal too!). And the Funny thing about those PWM Controlled Power Supplies is, that if something gets defect the Primary fuse is often still just fine!

      • Albert

        July 7, 2015 at 6:48 pm

        One thing I like to add concerning the users Safety is the fact that the X2 Special Safety Capacitor still could be charged after the adapter is just pulled out of the Wall Outlet. Which doesn't concern the controller circuit while it operates, and only uses some extra power while it functions. And I am refurring to an extra discharge Resistor of about 1M Ohm one could add over this Capacitor to prevent this from happening. I added the 1 Mohm to the prototype version shown but after translating my Tina circuit into an English version it somehow disappeared from my final circuit unattendedly.
        Mea Culpa!

      • Robert Calk

        July 9, 2015 at 3:40 am

        The main problem is when some curious children start messing with things. As long as a child can't get into the box, it would be safer, but transformers aren't that expensive. You can make your own transformers also. I like to make things as safe as possible, especially if a child could get ahold of the device.
        You are right that even with SMPS's there is no guarantee you won't get hurt, but the isolation makes it a safer device.

        • Albert

          July 9, 2015 at 5:48 pm

          Hi Robert, I understand your concerns. But as you say the "Optical Fan Controller" is isolated too. It is boxed into the sturdy adapter case. And placed just under the ceiling were no one can touch it.
          And even every transformer has two power pins that must not be touched at their Primary side at any circumstance. And when a child would take my Adapter out of the Wall Outlet to play with it there in fact would not be any real danger left!
          Just two days ago I opened up my Sony Cassette Dolby Tapedeck just to exchange the old rubber snares and grabbed unattendedly the Primary side of the Transformer side. It gave me a Hell of a shock but I let go at the same time. And I still remember when I as a Child out of curiosity put the 12 Volt motor wires into the 220 Volt Wall Outlet/socket. (it was still 220 Volt AC at that time). The Motor worked very fast for a very short moment and I survived. And there is no way to be sure that a child isn't going to do the same by poking around in things by using a metal screwdriver. Transformer or not.

          • Robert Calk

            July 9, 2015 at 7:45 pm

            I agree - there are no guarantees. We have to be as careful as possible. It sounds like you are in pretty good shape.
            I downloaded the datasheet of the X2 capacitor but haven't studied it yet. Thanks for the article and info.

            • Albert

              July 9, 2015 at 11:09 pm

              You're Welcome Robert. (About my 'Pretty good shape' : In Januari 2014 they defibrillated my Hart with normally Dangerous High Voltages in our Local Hospital. So it all is a matter of opinion).

              Safety above All. And mostly above the 42 Volt levels. Because if I'm correct that is the level at which Low Risk Voltages start to become Higher Dangerous Voltages. It means for an Electronics Engineer knowing how to build it the correct right way. NEVER without Fuses or saving on the right material or the right components. Good Isolation is a part of that. Not only to guarantee good working circuits but also preventing secondary hazards like Fire or RF emissions etc.

              Next excerpt from the Wikipedia about Safety and Voltages explains it very precise I guess:

              [Extra-low voltage (supply system) AC < 50 Vrms DC low risk]
              The numerical definition of 'high voltage' depends on context. Two factors considered in classifying a voltage as "high voltage" are the possibility of causing a spark in air, and the danger of electric shock by contact or proximity. The definitions may refer to the voltage between two conductors of a system, or between any conductor and ground.
              Voltages greater than 50 V applied across dry unbroken human skin can cause heart fibrillation if they produce electric currents in body tissues that happen to pass through the chest area.[citation needed] The voltage at which there is the danger of electrocution depends on the electrical conductivity of dry human skin. Living human tissue can be protected from damage by the insulating characteristics of dry skin up to around 50 volts. If the same skin becomes wet, if there are wounds, or if the voltage is applied to electrodes that penetrate the skin, then even voltage sources below 40 V can be lethal.

              But since we even can burn ourselves from a cup of burning hot tea, it doesn't mean we now stop drinking to be safe.

  7. Gerald

    July 8, 2015 at 3:49 pm

    Hi Albert,

    Good project, thanks for sharing. I was not aware of the "Tina" simulation software thanks for the tip. I will have a closer look at it. I have been using an old version of Multisim for simulation and SPlan when I need to just draw a circuit diagram. As you correctly said, Electronic Repairers need to do some circuit design time to time. It is fun and also good for understanding how circuits work


  8. Albert

    July 8, 2015 at 7:21 pm

    Hi Gerald, I know Multisim and have used it like earlier versions I bought of UltiSim and UltiBoard before they were renamed to MultiSim or how it is called to day. UltiBoard had extremely bad bugs that most users made working with it more complicated, like not knowing what symbol to use etc. from its database. Because the books that accompanied those earlier versions didn't help much either. And there are more programs today that help Electronic Engineers like Edwin (also from the creators of Tina if I am correct), Proteus etc. And the possibilities keep getting better. Because developing circuits writing in High Level Languages like VHDL or Verilog is becoming very interesting. Because it is FAST (200 MHz or higher working circuits we can now program in a Flash with the right programmers at home!) and the FPGA or CPLD chips get cheaper each day. There are different programmers for different IC's. That's why I bought one Xilinx programmer (their main software is Free), One Atmel programmer (their software has a 2 year free licence), and One Altera programmer (Not Free Licensed). And from all Programs the Atmel software is the easiest useable. The Programmers although all different, all use USB and a special JTAG interface to program and test/verify the ICSP/ISP connected Targetboard or FPGA/CPLD chips.
    And it is not the VHDL part that is difficult to work with or program in, it is the Programming Envirement that makes it hard to work with.
    You also can create your circuit in standard Logic symbols instead of plain VHDL or Verilog text. But a circuit with over 5 pages could be much easier modified in VHDL text as it would be in the 5 pages of circuit symbols. I made the effort to start with buying the hardware. Only running the software takes much more learning.

    • Albert

      July 11, 2015 at 5:43 pm

      Above I wrote that Edwin was also an Electronics Designer Tool from the makers of Tina. But I need to correct that. It is called Edison that is a simpler graphical version from the same makers that made Tina (DesignSoft). Although Edwin also is an existing Cad designer tool for Engineers, it is a completely different program.
      And I like to add that the more enhanced (more expensive) version of Tina also supports Developing in VHDL !

  9. Parasuraman S

    February 8, 2022 at 8:51 pm

    Happened to see it only today! Vow what an amazing and innovative creation! Hat's off!


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