[neilh20]

So just to add some more characterization measurements.

I’m using a Mayfly Sn 20395, and attempting to characterize what range the readings from the Mayfly ADC Vbat are linear when it is only powered from Vbat.  I’ve put a resistor network on the extV to the LiIon batter, to halve the voltage to keep it within the Vcc range for the ADS1115. Initially I used 100K//100K – and verified the output is linear.

I’ve connected an external  powersupply to the Vbat, an external Meter (Materman 37XR) and then making measurements

Power supply to Mayfly JP1 Vbat (instead of LiIon)
Adjust power supply voltage to desired V measured on Meter.

My conclusion is that the Mayfly Vbat becomes nonlinear under 4.0V.

TimeStamp	Meter	extVbat	adcVbat
12:28:00	4.225	4.208	4.291
12:30:00	4.103	4.090	4.139
12:32:00	4.106	4.092	4.139
12:34:00	4.00	3.989	3.957
12:36:00	3.90	3.889	3.760
12:38:00	3.80	3.793	3.563
(break)
13:22:00	3.79	3.794	3.578
13:24:00	3.70	3.691	3.517

 

Attachments:

1. 

   TU_RC_test04a_2020-10-15calibrV.jpg
   

1. TU_RC_test04a_2020-10-15calibrV.xlsx

[neilh20]

Hi Matt, power is a challenge. I always think of those battery watches with a tiny battery in them. How do they do it.

My take is this. a) what is the minimum energy its going to collect across the really low solar months  eg winter months  b) What is the longest I want the system to run for with no solar power – that is usually a storm of some sort.

Then the stored power can be budgeted into two sections – one for the time period that it needs to be working/sampling to run with no solar energy input, 2) when there is “excess” energy that can be used to transmit the readings to the cloud.  An assumption in this is of course that the readings will be stored (on uSD), and when there is available energy can be reliably delivered to the cloud . (https://github.com/EnviroDIY/ModularSensors/issues/194)

The current Mayfly charging circuit assumes a relatively low impedance on the solar side, and for all practical purposes its easy to over specify the solar panel to 5-10W (for Mayfly) so it is likely to delivery the 0.5A at 4.5V when ever there is solar power there.   For a 4Ahr battery, it would be charged in 8hrs  ~ a summers day but in winter?

On the consumption side  – I’ve put a spread sheet together in mA-secs or mA-minutes to estimate usage. So using mA/minutes a 4Ahr battery has 4,000mA*60minutes – 240,000mAmin.

For 24hrs if sampling is every 15minutes and takes 0.5min of running current – say 38mA and the other 14.5min are at a sleep current of 2mA. Then every 15min it consumes 38*0.5+2*14.5 or 17+29 or 46mAminutes – and in a day – 96 sampling periods ~ would take 4,416mAminutes. So for 4Ahr this would likely last over 54days without any solar power.  However with the battery power “budgeted”, if the 4Ahr can be divided into 2Ahr for communications and 2Ahrs for guaranteed core taking readings then using 4,414mA it would have 27days.

I’ve created a Battery Management System to be able to partly implement this in a “simple” way. Yet to be entirely proven.  The basic premise is that at critical points in the program a call to the BMS asks is there enough power for the operation to be performed? One of these points, after wake up is to check if there is enough power to transmit readings. If the answer is NO, it just does logging, if Yes it does LoggingAnd Transmisson. (Uses the current Class entry points)

So far I haven’t considered the power cost of transmitting the readings to the internet, as its expensive in power, but this would only happen when there is enough power. So a separate budget power exercise needs to be performed for the cost of transmitting, but it can be gated so it only does it when there is sufficient power (for a winter that might happen  after the sun has risen enough to be charging the battery).

In practice the LiIon voltage is partly dependent on ambient temperature (cold in winter), and Mayfly mega1284  Vref tied to Vcc at 3.3V, and combined with charging/Solar input. So Vbat does not reflect LiIon battery at all times. So for NO solar the Vbat ADC results are accurate from 4.2V to about 3.6V, when it becomes non-linear due to power cct LDO dropouts. For ~~good~~ solar the Vbat ADC reflects how well the battery is being charged and is likely above 4.2V ~ mostly not a problem.  So hopefully the Vbat absolute voltage could have a number 3.8V? (…. 3.9V) that is  crudely interpreted as a  50% (or 75% ) “fuel gauge”  for a reasonably large LiIon battery. The problem may be when there is weak solar, and when the Vbat absolute readings are taken may indicate a solar charging voltage, that doesn’t reflect the power stored in the battery. The Modem takes power at different time than when the Vbat ADC reads the LiIon voltage ~ so there could be nonlinear Vbat readings just at the most needed time when the LiIon is run down. That is with a weak solar charging current the Vbat is the solar charge voltage, not the LiIon battery voltage.   I’ve been investigating a separate battery monitor on the external ADC, and potentially also the  Xbee LTE’s has a voltage converter that can measure the Vcc (which should be ~ 3.3V).

https://batteryuniversity.com/learn/article/discharge_characteristics_li

For being able to do shorter time period testing I’ve been using a 500mA hr battery for testing the BMS transition thresholds, and I’ve built in an option for different types of batteries 2Ahr ..4Ahr with different thresholds.

Well hope its not too much detail, but I’d be interested if this going in the direction you think might answer your questions. 🙂

[neilh20]

I should note, that for real world solar panels, the power supplied by the panel is  dependent on the solar photons received. For a  slow change in power delivery some circuits have some strange behaviour.  I’ve had a Mayfly with an LTE  module, and a 2Ahr battery, and at sunset it started resetting. It continued resetting for about 30minutes until the sun’s power was completely gone. I had let it run and this repeated every night for a week.  I changed out for a 4Ahr battery and the resetting stopped. The 2Ahr battery was being fully charged every day, and when the sun was down it ran OK overnight – just in the twilight zone it had a problem. Was OK with sunrise.

I was monitoring the LiIon battery voltage with both the Vbat ADC and also externalV with 100K-100K divider. The Vbat ADC was showing a funny dip in voltage before it reset – but I never investigated further – just made sure I used the 4Ahr battery.   I am doing some characterization work how to measure a battery that is below 3.7V – but still ongoing.

[neilh20]

I’ve been using the INA219 and contributed sensors\TINA219
I’ve used it for measuring a working Mayfly on the lab bench. For  field monitoring, I would think you need a coloumb counter ~ eg LTC2941 ~ I have an adafruit version but haven’t tried it.

On the lab bench I have the INA219 on a separate Mayfly with console and put in in series with the target systems LiIon battery.
https://github.com/neilh10/ModularSensors/wiki/Test-equipment-cable-monitor-LiIon

For measuring a working Mayfly current I disconnect all other sources of power, and even have a special version of the FTDI cable to plug into the FTDI debug (instead of USB data/power) with the Ftdi Tx cut (as its held high and leaks current)
https://github.com/neilh10/ModularSensors/wiki/Test-Equipment-FTDI-cable

Using this arrangement, sampling every 2secs to get an idea of the instantaneous current
https://github.com/neilh10/ModularSensors/tree/release1/tools/current_logging

There has been past discussion on Mayfly sleep current. IMHO I’ve got to be in reasonable shape, but perhaps not meeting what a calculated minimum suggests it could be. https://github.com/EnviroDIY/EnviroDIY_Mayfly_Logger/issues/21

I figured for reliability of systems in the field a software based Battery Management System was more viable than trying to tweak down the sleep current. The target is reliable data collection, and reliable delivery for low cost LiIon/4Ahr battery and solar panel/5W.  Note the Mayfly Vbat monitor becomes non-linear at about 3.6V

The figures I got for Mayfly sleep was 2~4ma.  I have some notes that when I started taking measurements it was about 5mA. I did some tweaks got it down. Here are the measurements I made in my log with a Digi Xbee WiFi.
<h3>2018Dec12 sleep Current readings</h3>
with INA219 monitoring from another Mayfly
1st time through from RESET
02:13:24.972 mA: 3.80, V: 0.908
02:13:26.971 mA: 1.90, V: 0.936
02:13:28.972 mA: 2.10, V: 4.048
02:13:30.973 mA: 7.70, V: 4.044
02:13:32.972 mA: 4.00, V: 4.048
02:13:34.999 mA: 3.60, V: 4.048
02:13:36.999 mA: 38.20, V: 4.020 <sensors starting

02:13:38.999 mA: 38.20, V: 4.024
02:13:40.999 mA: 38.20, V: 4.020
02:13:42.999 mA: 38.20, V: 4.020
02:13:44.999 mA: 38.20, V: 4.020
02:13:46.999 mA: 105.30, V: 3.972 <1st time Xbee including setup
02:13:48.999 mA: 90.00, V: 3.972
02:13:50.999 mA: 107.20, V: 3.968
02:13:52.999 mA: 106.80, V: 3.968
02:13:54.999 mA: 107.20, V: 3.968
02:13:56.999 mA: 106.70, V: 3.968
02:13:58.999 mA: 53.80, V: 4.000
02:14:00.976 mA: 107.50, V: 3.964
02:14:02.977 mA: 121.90, V: 3.964
02:14:04.976 mA: 106.80, V: 3.960
02:14:06.977 mA: 106.80, V: 3.964
02:14:08.977 mA: 106.40, V: 3.964
02:14:10.976 mA: 121.10, V: 3.960
02:14:12.977 mA: 106.60, V: 3.956
02:14:14.978 mA: 107.40, V: 3.956
02:14:16.979 mA: 3.60, V: 4.028    <off sleep
02:14:18.978 mA: 3.60, V: 4.032
02:14:20.979 mA: 3.60, V: 4.032
02:14:22.980 mA: 3.60, V: 4.036
02:14:24.978 mA: 3.60, V: 4.03

[neilh20]

Hi Anthony, I would also be available for testing/helping integrate LoRa networking and I have some gateways. Wow great news to hear there is an implementation done.

For my local SSU I volunteer as Industry Advisor, and for last years Engineering Capstone project a student used an Adafruit LoRa module on a raspberry pi pretty effectively.
https://www.adafruit.com/product/4074 “LoRa Radio Bonnet with OLED – RFM95W @ 915MHz – RadioFruit”
I’ve also purchased but not tried the $13 Xbee
https://www.robotshop.com/en/lora-long-range-transceiver-bee-915-mhz-north-america.html

I got the low cost LoRa Indoor Gateway for testing “The Things Indoor LoRaWAN WiFi Gateway – 8 Channel LoRa 900 MHz”
https://www.adafruit.com/product/4345 $85

We also initially got some other gateways that where very complicated, but the one that is a low cost outdoor
Dragino OLG02 Outdoor Dual Channels LoRa IoT Gateway 915 MHz (NA)
RB-Drt-23 Ordered: 1 USD $84.00

One item to note, is that not all gateways are active on the ThingsNetwork (like mine).

The outdoor “Dragino OLG02” only implements in hardware two LoRa channels out of the 8 specified. This can easily be managed in the sending side as to which channels can be hopped. When I registered the Dragino OLG02 on TTN I specified there where only two channels available.

[neilh20]

Hello I’ve just had a request to quote for a number of water monitoring devices, each one includes a Mayfly. I’ve put on the response quote subject to availability of the Stroud Water Research Center’s Mayfly.

Is it useful to be able to indicate potential demand?. Its a pretty typical thing for selling that there is a demand forecast.
Some amazon listings indicate how many are in stock, that would be useful to now.
When I request amazon if I can put 20 units in my shopping basket it says there is only a limit of 10 allowed.

Just checking what the thoughts are for scaling availability?

[neilh20]

Hi James, thanks for the agupubs reference – very nice to see the LiDar work.
I had talked to a LiDar guy some years ago and they had said they didn’t think it would work for streams, but that ref is showing it very nicely.

I’ve used 20mA depth sensors with Onset loggers, and had a couple of UL6a https://www.utopsensors.com/pressure-measurement/level-transmitter/liquid-level-sensor.html
It depends on what accuracy you want and over what temperature range. As the pressure sensor is the most critical cost component, a low cost resistive element, usually has an uncompensated temperature range. If you are pretty confident in little water temperature range for the stream depth when you need the most accurate readings then they are very useable.
If, as I’ve blogged and mentioned above, you need accuracy at low stream levels when the water temperature may have a large (10C?) diurnal swing then too much error can creep in.
For ground water situations, the temperature may hardly vary and there can be a large range in water levels.

For a stream loading looking at peak flows seems like range of interest are at the upper end, and the rating curve probably has the most error in it. 🙂 Just a guess.

One way to try it would be to use RS485 wingboard that can take a switched +12V generator, and screw terminals, with an appropriate high accuracy and stable temperature 50ohm resistor 0.05%, (0.020A * 50ohms = 1V) feeding via plug-in lead into the ADS1115 ports on the Mayfly you can get a reliable accurate conversion (0.1%)of the 4-20mA to a digital reading.
The 4-20mA is valuable, as only two wires, and if the loop breaks ~0mA ~ its an error condition. If the line short circuits, then its typically over 20mA and again error condition.

I did give up on Utop when I got one of their sensors with a combined temperature sensors in it, and the temperature calibration was way off. I queried about it, and didn’t get a very satisfactory answer.

[neilh20]

Interesting idea for a secondary board, perhaps linked into the USB. I have heard it done before via the JTAG, but I don’t believe this is available for Mayfly.
Possibly the biggest question on issues like this is power budget. If there was a reliable power budget for a linux SBC (beaglebone.org) it would be relatively easy.

One area to track this new feature request could be
https://github.com/EnviroDIY/ModularSensors/issues/220

Just a thought, another potential would be to look at the value of a next generation board, with that capability built into the chip. Since that ticket @220, where I’ve identified a method on issues/220 on how it could then be upgraded, I’ve been keeping a lookout for methods. I personally like the SAMD51 of which there is a lot of software support, and has the port capability for managing halfduplex comms which is the core of SDI-12.

[neilh20]

Hey happy to contribute where I can.
My wife and I started a trip in Hamilton with some friends in 1990. Spent 2 months traveling round NZ as part of a round the world trip. 🙂

I have a fork of ModularSensors and focus on a small subset of sensors, scaleability through ability to build releases, download a defined binary of the code, and test specific configurations
https://github.com/neilh10/ModularSensors/wiki
As and when there is a request, if its useful, I’m happy to migrate from my fork back into core software. Personally I’m following the traditional path of a multistream development, git supports so well, and where its a good place to stabilize releases.

I’ve got a release of new features with reliable delivery to MMW that is working well with Xbee LTE.

IHMO, I’ve always found there is work in defining a sensor configuration, testing it and then managing the stability of it through defined releases.
Be happy to chat more.

[neilh20]

Hi James, great to hear someone else interested. I just got a “relative EC” working nicely and gave them out to be deployed last week.

The “relative EC” is to be able to measure stream disconnect. For the <<dry>> hot climate we have in California, looking to monitor when the stream goes dry.

There is no reason why it can’t calibrated. Need to pay attention to a few specific components, and of course determine what accuracy you want, and can get.

I’m in process of putting a package together as Open Source Hardware.
I’ve developed a board and MS sensor software that interfaces on the Mayfly Analog port using the internal ADC, (tested), for the “relative EC”.

It optionally, (not tested), can be built to be plugged into Seeed connector with the more accurate ADS1115.

So the unit spec iw to be standalone, with 40′ of cable, and bootnet access(walk up remove microSD) and looks like this
https://github.com/neilh10/ms_hardware/blob/master/ec_analog/Ec%20Asm%20with%20sensor%20cable%20(Large).jpg
and the internals running with an standalone 3.6Vbattery
https://github.com/neilh10/ms_hardware/blob/master/ec_analog/Ex%20Asm%20Top%20(Large).jpg

What is the Turbidity and Depth sensor you are looking to use ?
How are you looking to access the data?
How comfortable are you reading circuits and building a PCB from a BOM?

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