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.

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.

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.

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.

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.

Great, @peerv !
That's a very good idea.
Do you have reasonable power consumption ?

@chbla, I'm quite puzzled.
As it works on the breadboard, of course, I would chase for bad soldering. For instance, the mosfet gate controled by pin 7.

Any picture of the arduino pro mini ?

@chbla, you are right. As mentionned on the schema, it should be connected to GNDT (the triggered GND). And now I do understand your point.

@chbla well, yes. As the level adapter AND the booster are triggered only when needed (during the measure time), I don't see where it closes the loop.
By maybe I misunderstand something. Where do you loose some current ? The trigger pin from the HC-SR04 ?

QQ.

Yep ! And that's why it's fun !
But my zc detector will work too. My first tests are OK

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..;)

From my experience, the transistor (or mosfet) is key to allow enough current to the DC-DC booster. Otherwise, it will not provide the appropriate voltage because max current getting out of a digital pin from Arduino is around 40 mA.

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.

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'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.