Motion sensor to detect sneaking toddler

Once the kids are asleep at night, you can finally relax. Aahh. Maybe you want to stress down with a violent splatter movie with the volume at 11? In this situation you definitely do not want the kids to sneak around in the house behind you and watch the movie in secrecy. In that case you will have a lot of explanation to do. (Dad? What happened to the man's brain?). Or maybe you and your spouse are in your bedroom making new kids..? You definitely do not want the existing kids to interrupt such a beautiful moment. And difficult questions could possibly be asked.

The trick is to use a motion sensor outside the toddlers bedroom and a portable doorbell with visual and audible alarm. All possible crisis is henceforth avoided.

I bought one of these Nexa doorbells, and a...

... Nexa IR detector.

The problem with the doorbell is that is also chimes when someone are walking around in the house during daytime. It also chimes to loud for the intended purpose. Therefore, I added a volume control, that also serves the purpose as a on/off switch.

The doorbell is a simple design built around a 433MHz receiver

A 100k audio pot for the junk box does the job. I also tried with some resistors to limit the 100k pot with mixed success. It does not matter much for this purpose.

I drilled a hole in the front panel, and ...

Voila. A doorbell with a nice blue LED and fully adjustable volume with a Moog style knob. I glued some eyes to the doorbell to make it seem a bit more friendly.

Stopping and starting a pendulum clock with an Arduino.

The purpose of this simple build is to stop the pendulum clock from ringing every hour during the night. At about 10 in the evening the pendulum stops, and it starts again at 10 in the morning. The electronics is simply a micro servo driven directly from an Arduino Leonardo.

The idea was inspired by this video http://youtu.be/FZ_Zd7TeMg0. This design is using a stepper motor rather than a servo, and is admittedly a better design. Nevertheless, my prototype works, and it does the job. Before attempting to build a similar device, you should read the discussion on hackaday.com regarding whether starting and stopping the clock every day is harmful for the mechanism or not. Your mileage may vary.

It is worth noting that this is a build I did a couple of years ago, and the Arduino Leonardo used in the project is now used in  a completely different project. In other words, the above video is all that remains of the small project. However, I might build a new one in the future, since it was very helpful in keeping the house quiet during nighttime.

Bathroom ventilation using an Arduino

Introduction

 
High humidity levels in your bathroom can lead to a fertile breeding ground for microbes like bacteria, mold and mildew. This can trigger allergic or other respiratory problem. Additionally, humidity can also significantly reduce the lifespan of the materials used in the bathroom. In my house I have a air handling unit with rotor exchanger (Flexit SL4 R) which sucks air from the bathroom (among other rooms) and blows fresh air into the house.

Flexit SL4 R air handling unit (image from Flexit.com)

However, in order to make this unit efficiently eliminate excess moisture from the bathroom when e.g., taking a shower, I need to adjust the fan speed to its maximum before going into the shower. Since there is some manual labor involved in pushing the button, it is often forgotten, and hence, the bathroom is not proper ventilated.

The obvious solution to this problem would be to control the air handling unit with a humidity sensor placed in the bathroom. There are two problems with this approach: 

1. Setting the thresholds for increasing and lowering the fan speed is very difficult since the relative humidity can vary a lot during the year. I.e., when it is very moist, the fan might stay on continuously without being able to reduce the humidity in the bathroom.
2. The optimal place for the sensor would be in the roof, which is very visible.

A temperature-based approach

So I thought, what is the root cause of humidity in the bathroom?: Well, it is hot water. Hence, I did a test by measuring the temperature of the hot water going through the pipes into the bathroom while taking a shower. At the same time, I also measured the humidity in the bathroom.

Humidity (in %)  in the bathroom and water pipe temperature (in C) while taking a shower (the shower lasted from minute 5-15 in the figure)
 

Not surprisingly, there is a correlation between the temperature of the water into the bathroom and the humidity in the bathroom. The next step is to construct a device that measures the temperature and communicates with the Flexit air handling unit. This will let the Flexit unit increase the fan speed whenever a hot shower is taking place.

Temperature sensor on the hot water pipe

The Arduino-build

Since I wanted a solution with no visible cables or boxes, I decides to go wireless. Luckily, my local DIY-shop (Clas Ohlson), has a wireless 433Mhz temperature sensor (36-1797) which costs close to nothing.

ESIC Temperature sensor from Clas Ohlson

In addition I bought a 433Mhz receiver from Deal Extreme. It is a peculiar unit since it has a lot of pins I do not understand whats for and as typical for Deal Extreme is does not ship with any sort of documentation. Nevertheless, all I needed was VCC, GND and DATA. The latter connection does not come with a soldered pin and I really do not know why. (Typical Deal Extreme confusion). However, it is straightforward to see that the receiver and the data-pin works by connecting it to a scope.

Based on this guide (which is again based on this guide) it was easy to receive sensible information from the temperature sensor via 433Mhz on the Arduino

I decided to use a Arduino Nano (ehrmm... clone) on this build. The Nano from Deal Extreme does not come with a bootloader (so it can hardly be called an Arduino at all). I managed to bootload the Nano from an Arduino Mega using this guide from sysexit. Thank you for that.

433Mhz Flexit Fan control using an Arduino Nano

Back to my build. Once sorting out the protocol for the temperature sensor it is actually a super simple build. The Flexit air handling unit sets the fan speed to the maximum value when Pin 14 and 16 on J5 are connected. The purpose of this is to let e.g., a kitchen cooker hood or a C02 sensor control the fan in a simple way.

I used an 5V Omron relay to connect these two pins. An opto-isolator would have been more suitable since there is no current going, but I did not have any opto-isolator laying around the day I decided to build this circuit. You know how it is. A digital pin on the Arduino drives the relay via a 2N2222 transistor.


In addition I added a LED and a test button. The circuit is so simple that you can probably figure it out from the above picture.

The verdict

So how does the system work in practical life?

Flexit SL4 R, with wireless connection. Notice the iPhone 5V charger powering the Arduino

The system has been running flawlessly for two weeks now. The fan speed increases whenever the shower is used and stays on for about 20 minutes. I now have far less humidity in the bathroom. The nice thing about the system is that there are no visible wires since the transmitter is installed inside a water distribution cabinet (as seen above) and the receiver is installed in the same cabinet as the ventilation system. The receiver is powered by a iPhone 5V USB charger so I do not have to think about battery changes.

Future work

1. There is of course the possibility to measure humidity in the bathroom by using an additional wireless ESIC sensor. This requires only a couple of additional code lines on the Arduino. I might use one in the future, but for now I am satisfied by my water-pipe-temperature-based moisture exhaust system. 
2. I have my 3D-printer placed in a small room that has exhaust ventilation via the same Flexit device. In order to reduce the amount of fumes and nano-particles in the room, I always manually set the Flexit to the maximum when the printer is running. This is a very important matter according to a recent article. It would have been nice if the fan could do this automatically whenever the printer is running. I envision a future project here, using a 433Mhz transmitter connected to the Melzi board on the printer. To be continued...