Here is the schematics (freshly made for you :))

And here the part list:

• Arduino pro mini (3.3v with BOD disabled) or Sensebender Micro
• Ultrasonic sensor: ME007-ULS (available here)
• NRF24L01+ (I use the PA - LNA version for long range communication)
• NPN Transistor: BC548 (the B version if prefered)
• Base resistor: 1k
• 3.3V Step-up Voltage regulator: NCP1402 (available here)
• Logic Level Converter (available here): it says 3.3/5 but actually it's any to any voltage.
• Waterproof case (available here)

And finally here is my code (not cleaned, sorry).
0_1496348693347_DistanceSensebenderMicro.ino
And the Eagle SCH
0_1496348714531_Low power Distance Sensor.sch

And now, I realize that it may have been wise to upload that to openhardware.io :)

Regards,

QQ.

I'm following-up on this thread Sensor for pellet burner.
On my side, I have started to monitor my pellet burner about 1-year ago.
I'm measuring global power consumption of the boiler as well as departure and return temperature of the heating circuit.
Even though, I do that since one year only, I've been thinking about how to monitor pellet consumption for at least 5 years (yeah, failure is an option :) ).
What I have tested:

• IR sensor on the fan of the pellet convoying motor: it failed because it was too far
• Magnetic sensor on this same fan: same failure for the same reason
• Vibration sensor: the heater vibrates ...all the time :)

Now, I'm about to test something quite simple: mains presence at the convoying motor. This one is quite easy (I will show you how) to design and relates quite easily to the pellet consumption: 1 second equals x grams of pellet.

How do I know the time mains are activating the motor ? Well, a zero-crossing detector.

Beware, main resistance values are key: they depend on mains value, optocoupler characteristics and ..their power. Using the displayed value (56k) will keep the power under 1/4W. The optocoupler is a LTV-814 (cheap and efficient !).

Here is a quick schema of such a detector. I will keep you posted with the results.

Hope my experience will help others.

QQ.

Oh, for whom is interested, here is a (very very bad) schema of the setup :)

The finale update !
After numerous tests (using used batteries, adapted software and a lot of patience), it appears that the step up booster was not working under a certain voltage (around 2.7v).
Futhermore, the sleep time before distance measure was very variable.

I have questionned myself a lot and finally, my doubts went to the capacity of the Arduino to feed the dc-dc converter with enough current.
To fix this issue, I have used a BC548B transistor with a base resistor of 1K to drive the step-up converter. And, miracle, it works !
My finale test was with a set of used batteries delivering 2 V !

Now, I have a sensor that tests distance, temp/hum and battery level every 15 minutes. The average power consumption is 55 µA (25 µA during sleep time and 15 mA for 1 second during measures).

QQ.

I've found it...Yep, several months later, I've found it.
Actually, there were some ghost connections. I have cleaned the different soldering flows using an Exacto. Furthermore, I have re-done the connection (to the NRF and the batteries) using a pump...
And...tadah ! now the sleep current consumption is around 25µA.

;)

You are right, @NeverDie. Actually, my power supply is coming from a french power meter, that means a lot of noise - as I'm DC from a 50Khz AC :). So, I did two things. Adding a 330 pF capacitor at the entry point of my board and a 47µF right next to the NRF24.
Finally, I've upgrade my design to add a tantalium capacitor right next to the smd pads.
Global view:

Zooming the back with the polarized capacity (old fashion):

Front view:

New design:

Cheers,

QQ

Well, I've adapted the NewPing library in order to handle different clocks (using inline definition of millis(), micros(), ...) and....it works perfectly !
Now I have a low power, low clock ultrasonic sensor that will last for years on a set of 2 AA batteries.
If I'm not too busy, I might packed it up and publish it :)

QQ.

A quick update on this topic.
I have pimped it up using a ME-007 ULS sensor. This one is waterproof, more acurate and can measure longer distances (up to 8 meters).
After some issues related to delay between measures, it works like a charm.

With please. Here is a global schema of the pellet burner:

I have circled the part displaying the beginning of the pellet conveyor and the motor.

I will publish my voltage curve once I get enough history.

And yes, I do shut down the sensor (and the booster, and the logic level adapter) between measures ;)

Qq.

Well, @mfalkvidd, I think you got it ! Your piece of hardware sounds pretty good to fix my issue. In the meantime, I've looked after the exact electrical tolerance of the digital inputs and found the information you are referring to. I thought about using the pullup resistors of the digital inputs but it works only for high/low inputs..not outputs..!
So, basically, I think the logic converter is what I need. I will keep you postee.

@chrille, thanks for your project. Unfortunately, I'm very drastic on battery lifetime and that's why I'm using Sensebender. My setup allows up to 2 years of battery lifetime (measuring distance and temp/hum). And Sensebender works with low voltage (with no voltage regulator).

QQ

@Nca78, actually, I did not want to touch the existing cables to avoid any claim from the maintenance guy ;) And as I could not access one single wire, I had to find another way. Interesting enough, using the existing connecting screws was easier.

@zboblamont: the picture is quite not clear but the motor is very well protected to avoid any mechanical injury. And, probably as a consequence, there is not detectable magnetic field coming out of it.

@bjacobse: I have considered this as well (as well as some kind of a gauge based on pressure or anything else in the tank). But, unfortunatly, as this is a 7 tons / 11 m3 pellet tank, it is filled by a truck blowing pellets into it....making the life of the ultrasonic sensor really not long :)
Furthermore, ultrasonic sensor would be good to measure a level with a very large error margin. With my sensor, I will be close to a 1-gram quantum...measuring the current consumption very accurately.
For the story of it, I already have a way to measure pellet consumption in a rough approximation: but weighting the ashes :) :)

QQ.

@mfalkvidd absolutely. I have 6 various nodes (temp, power, ..) with period of update from 20 to 90 seconds..

And here the latest battery graph displaying two things:

• The first phase with not that optimal battery consumption (until Jan, 14th)
• The second one with everything optimized (after Jan, 14th).

QQ.

@zboblamont : it's not exposed under the tank and totally shrouded on the boiler side

@gohan: right, by I really don't want to touch the wires. And neutral and phase are inside a single cable with not enough space to put a clamp..;)

@mfalkvidd guess what…the capacity strikes again. I’ve soldered a 47uF right on the nrf24l01+ pins and…it works.
Would someone explain me the logic there ? The traces between the pins and the capacity were like 10mm long max.
Oh well.

Qq.

@bjacobse , I do understand your concern ! That was my challenge for the past months. But the combination of digital output to trigger on/off the sensor, low update frequency (15 minutes) and a low power ultrasonic sensor makes it possible (ser posts above).

Qq.

It is a popular request (just make a search on the forum to be sure..): Domoticz full integration !
Let's go further python/lua scripts with dummy sensors.

Regards,

QQ.

After a 4 years work, here are some samples of my pellet consumption.

Now, guess when I usually stop the boiler ..:)

Cheers,

QQ.

I have found a pretty good mix in terms of distance / price / power consumption / hard conditions support. Here it is:
link text