Smart din module
Of course there are lots and lots of smart gateways available at the moment, so what makes this one special? Especially the compact form factor and installation location. It’s not yet another device which always stays in sight, this one is placed in the meter cupboard (out of sight!). It uses on of the latest and cheap Wi-Fi module from Espressif, the ESP8266-12. Beside, it’s possible to directly control two mains loads from the module. And it’s possible to trigger on the doorbell press.
Some example cases
– Control devices from the smartphone and tablet from all over the world
– Making the home smart via the cloud provider: “folding the blinds automatically when it starts to rain within 15 minutes”
– Log data to the cloud provider to give more insight
– Build your own recipes on ifttt.com
The first design steps
In the first phase the powerboard on the bottom of the housing will be developed. The powerboard consists of a mains switching power supply, two relays and some connectors. Only through hole components are used on this pcb, no smd components. It’s always hard to check the maximum 3D space around available for components, therefore I always print the concept and check it in the real housing. Luckily there is some space available for the through hole components underneath the pcb.
It’s important to use a fuse after the mains entry in case of failure. I used a pcb trace fuse. Furthermore, it’s important to make sure there is enough space between the low voltage traces and the “live” traces. Therefore I drawed a cutout (milling) trace in the middle of the board, just to ensure sufficient isolation clearance.The width of the transformer is almost equal to the inner width of the dinrail enclosure! There is room for maximal 2 relays. It´s difficult to place all components and still be able to ensure sufficient clearance between de low voltage and live parts/traces. Overall it’s a close fit.
The electronic transformer has a very low stand-by power, around 0,3W if secondary circuit is in sleep mode! To further prevent energy loss, it’s usually a good idea to prevent voltage regulators and other power conversion circuits as much as possible. The electronic transformer has a secondary output voltage of 5V, this is also the operating voltage of the relays, so almost no power loss here 🙂
This makes it not only a smart device, but also energy efficient 🙂
The end result of the prototype:
No bugs on this pcb found luckily 🙂
The second design step
Lets start with the “smart” board. All chips and modules operate at 3.3V supplied by one 5 > 3.3V regulator, in my opinion and experience its always much easier to work with regulators instead of switching power supplies when using wireless communication modules. On the board there is an ESP8266-12. The board has 3 leds to provide feedback. Beside these indicators there is also a button present, the button can be used to activate SoftAP mode to connect the Wi-Fi network.
As you can see on the picture one is assembled with the Espressif module. As you probably also noticed, there are some bugs fixes already 🙂 I forget some lines to connect…. aarrghhh…. Furthermore there is a small cutout below the white colored connector, to allow the flat cable to reach the power supply board.
In the meantime I succeeded in creating a simple config page to easily connect the module to a home network, see the picture:
Update 01-09-2015: still working on software, basic functions are operational, but a lot of improvements/bugfixes has to be done.