After the first idea was born a project name and prototype was created:
The project name “How was your day, darling?” or shortly “hwydd” refers to the interaction of the device. After you come home you take it in your hand and the device tells you how its day has been. A neat little reactive device.
As you can see the whole project fits into half a ping-pong ball.
To give you a impression how it works a little video:
If you take the device in your hand the warmth of your body triggers the device. You cannot see it in the video since it is too dark, but the flashing in the beginning signalize that it detected a human interaction (the device is getting warmer over a certain period of time.
In the beginning it is playing back the night (which is obviously quite boring – I will change it later). After the sun goes up and we had a very nice morning – as you can see. The afternoon was quite bad weather – therefore it gets darker – until it gets dark again since night falls
The light is recorded by using a SFH 3310 phototransistor. To react to human interaction a stock thermistor (the small black thingy on the bottom in the first photo). For measuring and storing the results I used an ATTINY45
The schematics is very simple:
The photo transistor and thermistor form voltage dividers and are connected to the analog input of the ATTINY45. The LEDs are simply connected to digital and PWM outputs of the ATTINY. Add a battery and a programming header and you are done.
Translate this into a physical device and you get this (OK, next time I will use a little bit less messy wires):
As you can see I had to swap the photo diode to a stock one – I simply got the SFH 3310 too late. Next version will have everything.
The bottom line:
- The LED is far too dark. 3V ain’t enough for the white LED.
- Recording 24 hours is far too much. The twelve hours of night are just boring!
- The human warmth detection is OK, but needs some optimizing.
- The project was far more complicated than I thought. Especially reducing the power consumption got some serious attention. But in the end it runs for weeks from a single coin cell.