Inspired by two post which you can find here and here, I bought a couple of IKEA Molgans for €4.95 each. The Molgan comes in a nice enclosure, a housing for 3 AAA batteries and a PIR motion sensor. Unmodified the sensor will be active when it gets dark and switch on four legs if it detects motion.
I will modify the Molgan so that I can use it in my Home Automation installation as Multi Sensor sensing motion, temperature and humidity.
The first step is to open the sensor by removing the plastic dome. It is kind of glued so you need a knife or screw driver for that. After having it opened it looks like that.
First remove the photo diode which is located at the lower side on the picture above. If you leave the photo diode the whole thing will only work in dark.
Then loose the screws and unsolder power supply contacts in order to remove the board. The contacts need to soldered back again later.
Once the board is loose turn it around and you will get access to 3V coming from the onboard regulator and the PIR contact which goes high if motion is detected.
3V can be accessed from the upper left pin of the BISS0001 which is the control chip of the motion sensor. I soldered the red cable to it which will serve provide power to my Arduino. The “motion” pin is the second from from the upper left to which I have soldered the yellow cable.
Before you can put the board back again you need to remove the resistor R12 to R16 in the upper side of the board.
Instead of a Arduino ProMini which I use in most of my MySensor module, I used a Sensebender which costs 14$. Although significantly more expensive than a Arduino ProMini, the Sensebender is an Arduino compatible board which has already a temp, humidity sensor integrated as well as the crypto chi ATSHA204 which I am using on all my sensors. The Sensebender has been created by the MySensor community. Further, it has the advantage that is small and compact and easily fits into the enclosure.
Next the radio NRF2401 which you can buy at Aliexpress for around 1$ is soldered to the Sensebender. How the radio has to be connected is documented at MySensor. The motion pin is soldered to pin 3, power and ground to the respective pins.
Finally I decided to measure battery voltage using a voltage divider. I used a 4.7MOhm and a 10MOhm resistor. From the measurement point to ground a 100nf capacitor is soldered (a good article can be found here). The measure point is soldered to pin A1.
Before staffing everything back into the enclosure the Arduino sketch needs to be uploaded. The sketch can be accessed in my Bitbucket repository.
This is the final multi sensor before mounting the plastic dome back.