Sensebender Micro

filipq

Got it from http://cpc.farnell.com/1/1/57932-evatron-pp42m-case-sensor-ivory-71x71x27mm.html.
Not the cheapest, but definitely worth the money as it is very good quality. There are other colours available (white and black) https://www.jprelec.co.uk/store.asp/c=552/Gas-Sensor-Case

scalz

@tbowmo: I have some of these too, it's nice box. i got these from tme. cheaper :)
http://www.tme.eu/fr/details/box-sens-white/boitiers-dappar-dalarme-et-de-capt/supertronic/

ahmedadelhosni

Hello @tbowmo

Doesn't the atmega328 has only 2 pins which are D2 and D3 from external interrupts ?
I am wondering why do we waste the usage of D2 since the IRQ pin is not used in the library ?

Anticimex

@ahmedadelhosni because it is not in use by the library <yet>. Would be a shame if the library some day gets updated with support for a radio that can enter low power sleep and still wake when needed.

tbowmo

@ahmedadelhosni

What @Anticimex said.. And at the time when I created the sensebender, I didn't know that the interrupt wasn't used (I was relatively new to the project) so I thought that we had to have it connected..

hek

It is used by the RF69, right @tbowmo? (when using adapter plate...)

ahmedadelhosni

@Anticimex @tbowmo This a valid point which I thought of but I needed two interrupt pins. As far as I knew from fast searching is that external interrupts which react to CHANGE in pin state are only valid for pins 2 and 3. Correct ?
Maybe there is another solution which I missed.

tbowmo

@hek

Yes, that's right, RFM69 is using interrupts.. (and rfm69 is possible on the sensebender using for example this pcb)

Anticimex

And with a scalpel and a soldering iron you should be able to use both interrupts by disconnecting the one reserved for nrf24. Of course that would disable the use for rfm69 om that board.

ahmedadelhosni

@Anticimex Yeah I could just connect my device to the atmega pin directly as I can see/find any pin header to route the interrupt pin 2. They are all used.

Thanks guys.

TheoL

I just received two sensebenders. I'm really impressed by the great engineering behind the board. I can't wait to heat up my soldering iron. I love them!

user2334

I just received two Sensebenders, but have problems getting the device to consume little power. I get totally different values as displayed above.

With the following sketch, I get about 5,6mA in active state and 1,6mA in sleep mode with nRF24 attached. I have compared different nRF24-chips and this one consumed the least power.

Without the nRF24, I get 4mA and 0,025mA (=25µA) during sleep mode.

#include <LowPower.h>
#include "RF24.h"

RF24 radio(9, 10);

void setup() {
}

void loop() {
    delay(8000);
    LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
}

mfalkvidd

@user2334 I don't think the LowPower library shuts off the radio. Use MySensor's sleep function instead.

ximinez

A general question regarding these types of boards that are generally designed to be used on battery power. Is there a reason to not power the ATSH204A and Si7021 from AVR pins? The pins can source far more than what these devices can sink (even when using the heating on the Si7021), and it would allow squeezing a tiny bit more out of the battery life by selectively powering down the devices.
Eg., if I'm not using the ATSHA204A at all, I can save 150nA continuous current. The power saving from disabling the Si7021 is less at about 60nA, so that might just be eaten up by having to wait up to 80ms before a full conversion.

I'm aware that we're talking about saving a tiny ~200nA here, but over the span of two years that adds up to about 350mAh.

So what I'm wondering is simply, is there a technical reason saying that this really isn't a Good Idea (tm)? Should I avoid doing so if I design my own similar device?

LastSamurai

@ximinez said:

A general question regarding these types of boards that are generally designed to be used on battery power. Is there a reason to not power the ATSH204A and Si7021 from AVR pins? The pins can source far more than what these devices can sink (even when using the heating on the Si7021), and it would allow squeezing a tiny bit more out of the battery life by selectively powering down the devices.
Eg., if I'm not using the ATSHA204A at all, I can save 150nA continuous current. The power saving from disabling the Si7021 is less at about 60nA, so that might just be eaten up by having to wait up to 80ms before a full conversion.

I'm aware that we're talking about saving a tiny ~200nA here, but over the span of two years that adds up to about 350mAh.

So what I'm wondering is simply, is there a technical reason saying that this really isn't a Good Idea (tm)? Should I avoid doing so if I design my own similar device?

I second that question. I was just thinking about a similar idea.

tbowmo

@ximinez @LastSamurai

That is indeed a good question. The straight answer is that I didn't think about that when I designed the board.

In theory you could also power the radio from a digital pin on the avr, and power that down completely.

BTW. If you turn on the heating element in the si7021 at full power, I think the power drain exceeds what the avr can deliver on a digital pin. But one could just avoid that.

Anticimex

I have been thinking about this as well. But I discarded parts of the idea because I needed the IO for other stuff (MYSX in my case). Instead I designed a switched rail where one could attach sensor power sinks. It's not io powered but it is io controlled.
Though I did not attach the si or atsha to this switch function as I decided to make it an optional feature but wanted to make sure authentication and temp/hum would always be available.

ximinez

That is indeed a good question. The straight answer is that I didn't think about that when I designed the board.

Oh, I thought it was a design decision :)

In theory you could also power the radio from a digital pin on the avr, and power that down completely.

I've been wondering about the radio in particular. Does the radio keep any state locally, and will it have to be reinitialized upon powerup?

BTW. If you turn on the heating element in the si7021 at full power, I think the power drain exceeds what the avr can deliver on a digital pin. But one could just avoid that.

The heating element eats a measly 3.1mA according to the datasheet, so even that would be well within the limits for a single in on a 328p.

Now, I don't have Eagle installed on this laptop, and my bandwidth is limited right now. Is there a picture of the PCB traces available? Wondering if atleast some of this can be hacked on by cutting traces.

tbowmo

@ximinez

Nope, there are only the eagle design files.. (Or gerbers, you could use a gerber viewer)

I have 4 sensors operating for almost a year on two AA batteries, they all report around 73% battery left. So in my opinion, it's not that necessary to do extra optimization on the power drain..

ximinez

@tbowmo
While 73% after one year is good, it doesn't mean that it can't get better. The ATSHA204a and Si7021 draw about 350mAh from the battery over two years from idling alone. The NRF24L01+ draws around 1500mAh.
Remember, you will never get close to emptying out the battery before the voltage drops below working voltage. Using alkaline batteries, you'll get around 2000mAh before the batteries reach 2v (which, if you're using battery voltage as a pure percentage, is 66%), at which point the voltage curve drops sharply - and your sensors die. The radio and sensors have drawn more than 900mAh from your battery during the year you have run the device (and that's just idling) - close to half your battery life.

Assuming your battery percentage is correct, and you started at 100% one year ago, I'm betting your sensors will die sometime during this summer. While you may think that extra optimization isn't worth it, I do. The nanoAmp draws may not seem like much, but drawn out on a timescale like this, it is a major power draw.

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