2AA Sensor Board + RPI Gateway + RGBW Dimmer



  • Hi everyone,

    I was close to buy a Fibaro complete set until I discovered MySensors Project. This project is really cool, I'd like to thanks everyone involved in it. I'm more an hardware guy, so I wanted to do a little sensor board that I can spin for 10 units or something like that to cover the needs of my apartment.

    I decided to design a little sensorboard that fit on the back of a 2AA holder ( 58*33mm) that can fit all the sensors I would need. The idea is that once you have the PCB, you solder just what you need on it. But it can work with every sensors populated also.

    After days of reading and comparing sensors / supplies solutions, these are the specifications I choose:

    • Works on two AA batteries in series. Use an MCP16252 to generate 3.3V that is enabled by default but can be switched off (and so bypassed) by the MCU if the batteries voltage is enough.
    • Battery voltage monitored by the MCU
    • Arduino compatible atmega328p design. External 512k spi flash for future OTA
    • RFM69HCW design. It seems this is better for range and overall reliability ?
    • PIR sensor: Custom design with the E931.96
    • Light sensor: TSL2591
    • Temp/Humidity sensor: Can use SI7020, HTU21D, and SHT2x range from sensirion
    • Pressure sensor: BMP280
    • IMU: MPU6050, MPU9255
    • Two RGBW 5050 LEDs
    • Extension connectors that can be used to stack extension board on top of the PCB.

    I estimated it could achieve 1 to 3 years of battery life. I try to implement every hardware energy saving possibilities (hardware interrupts, ...).

    Have you any advice or comments on this ? I have zero experience with MySensors and these sensors, so that could help. Here is a preview of the PCB : (routing still in progress). If anyone would like to see the schematics, I just need to clean it to release. This will be open source hardware if anyone is interested.

    mysens1.jpg

    Myna



  • Overview of the schematics (no values yet) : sch01.png


  • Hardware Contributor

    Hi.
    great work! It looks good ;) I think you could add authentication chip.
    I have made a similar board, ultra low power with lot of sensors. I am using mosfet to disable what I want radio or sensors. I don't use wdt, I made a hw wdt with a supervisor chip. But you are on the right way with your booster ;)
    I will update my files asap if it can help you..
    I didn't know E931.96. it seems exotic chip .Did you try it, do you know its power consumption in operation? I say this because I made a small low power pir breakout (I'll post files asap) but I am very curious with this chip, is it another sort of BISS0001...
    Good luck for your routing :)


  • Mod

    @Myna said:

    Use an MCP16252 to generate 3.3V that is enabled by default but can be switched off (and so bypassed) by the MCU if the batteries voltage is enough.

    I like the idea, but how is the MCU powered when it switches off the batteries?
    Seems to me that +3V3 will not receive any juice then.



  • The PIR sensor if probably the part that gives me the more difficulties and I'm still unsure. I started by looking at what Fibaro uses:

    https://community.smartthings.com/uploads/default/original/2X/5/5d538a18103afa8dc33f1cd9827991b24cb2d62b.jpg

    It's an Excelitas PYD1698. It looks like a great chip, low power, everything included... But it seems nearly impossible to source in low quantities. I was not able to find a datasheet. Maybe it's worth sending Excelitas an e mail, but by experience, I don't have that much hope.

    Then I found the exotic chip E93196. It has everything in it, is low power, digital communication, and gives you a programmable interrup, for good price. Datasheet says 8µA : http://www.hsinbao.com.tw/administratorHB/caproduct_data/pdfs/E93196_12_wm IG.pdf

    I'm balanced between simplicity and low power choices. Standby currents for about every sensors I choose seemed "good enough" compared to the global consumption. I first tough of multiple power rails, I could go as low as 2.5V, but then I can't use the white, green and blue LEDs. Also, the performances of the radio seemed not really knowed at these levels. So I want for simplicity : one 3.3V rail, with a regulator that the MCU can bypass during sleep periods if the batteries are > 1.8V.

    The RFM chip offers AES Security, in this case, is the authentication chip still usefull ?

    Thanks ! I'm checking your work, very inspiring !



  • @Yveaux said:

    @Myna said:

    Use an MCP16252 to generate 3.3V that is enabled by default but can be switched off (and so bypassed) by the MCU if the batteries voltage is enough.

    I like the idea, but how is the MCU powered when it switches off the batteries?
    Seems to me that +3V3 will not receive any juice then.

    Hi, the MCP16252 is special : when disabled, it connects the output to the input with an internal P mosfet. The MCP16251 is the same regulator with output disconnect when disabled.


  • Mod

    @Myna said:

    when disabled, it connects the output to the input with an internal P mosfet

    Ah, already thought it would be something like that, but didn't look up the datasheet.
    Nice feature though :+1:



  • I made a crude sheet to estimate the price and batt life impact of each part.

    Clearly, the MPU is the worst part. But I don't expect to use this sensor often. But even with these numbers, the full board would last 7 years in sleep mode.

    tab1.png


  • Hardware Contributor

    cool.
    just for curiosity, did you calculated all res tied to gnd, like dividers, sort of low power killers? Is it your bus current data?



  • @scalz said:

    cool.
    just for curiosity, did you calculated all res tied to gnd, like dividers, sort of low power killers? Is it your bus current data?

    Not yet. I'll use the biggest possible values to loose as few as possible power in theses...

    I'm thinking of wiring the supply of the flash memory chip on the CS. So, the chip will only be powered when selected on the spi bus. Easy mod, because the CS is already there (not the same with I2C...)



  • Hi !

    Some news:

    I've finished the drawing of V1.0. The main change is the following: Pressure sensor and IMU removed. The idea of this board is to be the universal sensor, and make it multiple time. I couldn't really find an use for these sensors. If I need them, it will be on one board, and so a little extension board is OK. Also, it save a bit of space for cleaner routing.

    So it will be Movement/Light/Temp/Humidity/RGBW LEDs/ (Extensions)

    The board size is 35*60mm, the idea is to solder this model of battery holder under it: 42767313.jpg

    I've started to order some of the components. I didn't ordered PCBs since 2013, is Seeed/Itead still the way to go for cheap good PCBs ?

    The board:

    mynaV1.jpg

    Silkscreen is in yellow. Is it OK to use the logo of MySensors as I did ? I prefer to be sure...

    Myna


  • Hardware Contributor

    @Myna Very nice board ! As to your question about PCB manufacturing. Seeed/Itead is certainly an option. I have been suprised (in the positive way) by the quality of the boards made by DirtyPCB. It takes a lot of time to get them shipped to Europe, but production quality is good. 14 USD for 10+/-1 boards of 50x50mm is certainly very good value. Your board will probably fall in the 100x100mm category as it exceeds 50mm on one side, but then you could probably panelise it. For 3 PCB samples, and shorter lead time (and any combination of size) I have used OSHPark, but at higher cost.
    Did you make this board in EAGLE or in KiCAD ?



  • Thanks Gert ! It's Eagle 7.3.0 light. Maybe not the best but the one I know... (I have the idea of switching to Altium)



  • IMG_20151120_180219.jpg



  • Hi ! A new board today :

    I don't have any gateway or controller at the moment, and I plan to use Jeedom on a Raspberry Pi 2. So I've routed a little serial gateway for RPI. The board use the native serial port of the RPI (tough it should be more stable than going trough an usb/serial chip ? ). Also, I added a 3.3V LDO so that the gateway don't use the RPI 3.3V and a RGBW for monitoring / debug purposes.

    mynagateV1.jpg

    The idea is to fit this and the raspberry in a normal enclosure. It should just need a hole for the SMA connector :

    rpigate.jpg

    Any advice for RPI cases ?

    Myna


  • Mod

    The 3.3V output on the Raspberry Pi is rated for 50mA maximum current, which is plenty for the standard nrf24l01+ (specification says <15mA), but if you are using a radio with a power amp you might need more so the ldo could be a good idea.
    I am using this case because it has a hole for the gpio ports.


  • Hardware Contributor

    @Myna Again a very nice board ! Since you made it in Eagle, you could just drop your .brd file on OSHPark and they will make it for you. I also dropped my latest 7.3.0 Eagle files there without a problem. Make sure you download the design rule file and check the board with it.
    I made a DRU file which covers all limitations for OSHPark and DirtyPCB so that I can be sure that both can handle my designs.
    Gert_Sanders.dru
    Just rename it to whatever as long as it keeps the .dru extension and place it in the DRU directory of Eagle. I have used this DRU for two designs made by both PCB makers without a problem.
    As for cases, I think most have a cutout for the camera ribbon, so you could enlarge that!
    Here is the case I use:
    IMG_7301.jpg
    I got my case from here: https://www.antratek.com/raspberry-pi-model-b-enclosure-clear



  • Thanks guys ! I think it will be itead studio as it seems they have the cheaper price for 5*10cm. I've checked the board with Seeed DRU.

    The last board : an RGBW and DC PWM dimmer. I'm really into lighting design, so that's very important for me.

    **Specs: **

    • 5 to 24V input. Work with 5, 12 or 24V led strip or power LEDs.
    • should handle 3-4A per output with no problem. AO4496 Mosfets. (depend of PWM frequency)
    • measure of the LEDs supply voltage ( resistor bridge to ADC)
    • measure of the LEDs supply current (sense resistor, INA138 to ADC)
    • DATA and GND header to drive intelligent LED strips (WS2812 , etc)
    • Power and LEDs / LED Strip connection trough 3.5mm screw headers
    • OTA hardware (spi flash), RGBW 5050 monitor LED, expansion ports as usual

    mynaLEDV1.jpg

    Now let's final check the board and make the order !



  • It is interesting, what is the status ? ,
    Have you have tested the 2AA Sensor Board + RPI Gateway and it works well.


  • Hardware Contributor

    Cool! Have you considered the MYSX connector?


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