About duration in case of battery presence


#1

Hi all
thanks for BLUZ, it really seems what i’m looking for…
I have a big … big … curiosity. One of my project needs a battery power to implement some features whit a MCU. I’m thinking about ATTiny with ble module, but BLUZ seems perfect.
The situation could be this:
the BLUZ MUST be always connected to its Gateway, and receive commands from it. It receives more or less 50 commands per day (not more probably) , and it must manage a relay 5v after each command. Consider that i have not a “space” problem , i can use cell bat or rechargeable AA battery (or lithium battery … what you want). The Gateway is linked with a wall power , so there is not issue for it. The area is more or less 70ft with 10/20 bluz in each area.
Can i have an idea about the duration of a recharge in this situation?
thanks
Mirko


#2

@infor_mare, the gateway can only handle 8 bluz being connected to it so the 10/20 bluz per area will be an issue though I defer that to @eric.

As for power, you say each bluz must manage a 5v relay. If you expect the battery to power the relay then this will be your main power draw, not the bluz. Are you expecting to use a “latching” relay which only needs power when it changes states? Without this, when the relay is “on” or powered, the battery will deplete quickly since the current draw could be large (20ma/h+ depending on the relay).

You may want to consider powering the bluz with a CR2032 button battery (or rechargeable) and the relays with a separate battery pack. :smile:


#3

yes , this was my idea. Consider that i only need an impulse by the relay.
In that situation, the BLUZ duration?? And if i use 2000mA pack for the bluz too? (not the cr2032)

Thanks
Mirko


#4

@infor_mare, I can’t speak to the power requirements of a sleeping bluz but it is very low in sleep mode. Since you are pulsing the relays, power consumption will be low so you are probably looking in the order of 15+ days but this is totally off the top of my head. More data on the relays and hardware design are needed. Ultimately, you may need to get a bluz and characterize your configuration to get actual numbers.

One thing to remember is the bluz runs at 3.3v so you will need an opto-isolator or MOSFET interface to drive it (neither of which will draw any significant power when unenergized).


#5

Mileage will vary, and all this is highly dependent on your specific configuration and code. A highly tuned bluz board should be well under 100uA in your case, awaking only to transmit at connection intervals (which will be tunable) to maintain the connection. If you set your connection intervals way down, on the order of seconds, then the time spent transmitting is very minimal. I am also ignoring any power needed to drive any external devices.

So, rough back of the envelope calculations, you would get something like 2+ years of usage from each board with a 2,000mAH battery. Please understand this is just a ballpark number, you could get even more (or a lot less) depending on specific configurations and code.

As for the number, yes, each gateway will support up to 8. This can be extended by adding more gateways or looking into a different gateway solution (raspberry pi with a bluetooth LE dongle, for example). The latter of these is something I am contemplating more and more, though it will probably get pushed well into next year (unless someone in the community wants to take this as a nice side project :smile:)


#6

@eric, so between my really pessimistic 15+ days and your 2+ years it’s fair to say that with careful power management on the peripherals, the battery life will be at LEAST 1yr. NICE! :smile:


#7

It seems a dream … 1 or 2 Years should be perfect.
In this case i need to undestand better the sleep mode…
In sleep mode , can a Bluz receive a command in the BLE side? My issue is that these features are “real time features”, for example open a door, or switch on a lamp. If the Bluz , that manage the door (for ex) is in sleep mode, how many seconds i need to close the command and open the door?
thanks for your time


#8

That is the magic of BLE!

Outside of normal problems with responsiveness (internet connection, interference, cloud response time, etc.), the biggest variable will be the connection interval. BLE will sleep and wake up each connection interval to do a quick check with the gateway and see if data is available. It’s always a tradeoff, to get super responsive you want this to be as low as possible, or your application may have to wait longer to get data through. But the higher you set it, the more battery capacity you will consume since you are waking up more.

In BLE, you can set this value anywhere from 7.5mSec up to 4 seconds. It is actually controlled by the Central device (the gateway for bluz), not the peripheral, so you would have to set it in your gateway. So playing with that value is key to make your app responsive yet power efficient.

But outside of that, yes, you will get that kind of battery life with real time responsiveness.


#9

Now it is clear … thanks for your support.
Please send me my order asap … :smiley:

thanks
Mirko


#10

So much to learn and so little time!