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neilh20

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Viewing 10 posts - 341 through 350 (of 371 total)
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  • in reply to: RS485/Modbus RTU Transducers #1845
    neilh20
    Participant

      I received my dual relay board,
      * AtomicMarket.com: 5V Two 2 Channel Relay Module With optocoupler
      * SunFounder: 2 Channel DC 5V Relay Module with Optocoupler Low Level Trigger Expansion Board
      and the code to drive the relays is pretty simple and is here:
      https://bitbucket.org/neilh20/anuttx/commits/daf3e4199ec66c158a3ef20e0da64ec0bcb9f7db

      The purpose is to be able to switch +12V to a Nanolevel capacitance depth gauge and read it over RS485. I’ve been running some tests with the Nanolevel querying it over RS485, and the results have been pretty stable as temperature has varied. However in the solar powered, minimal power useage, the Nanolevel needs to be off most of the time, power switched to it when its going to be used, a pause to allow it to stabilize, and then read it over RS485.

      neilh20
      Participant

        Hi Marion,
        I don’t have any experience, and it would be great if you share what you find here.

        This is a topic the EPA is sponsoring – with a target of unattended for 3 months –
        http://www.act-us.info/nutrients-challenge/

        And they have a short list
        http://www.act-us.info/nutrients-challenge/Participants.php
        regards

        in reply to: RS485/Modbus RTU Transducers #1827
        neilh20
        Participant

          Well my first post on this is to talk about the powering – not as sexy as the protocol, but a base requirement.
          Since this is wired, each transducer is going to require power.
          Getting powering right is ALWAYS a challenge for a circuit, especially solar powered, low power useage circuits. Its vital to understand the impedance of the power issues.
          Wall power supplies are constant impedance and relatively low impedance sources – they can supply say 1 to 2Amps no problem.
          Solar panels are variable impedance and relatively high impedance power sources – when its dark there is no power, when the sun is shining it has some power. Batteries and capacitors manage the impedance profile change between a solar panel and the dynamic power used.
          In an experiment with a low cost Utopia ULB-I depth gauge – which requires 8-36VDC I recently hit some of the power issues.
          It is an example of transducer, and the specification is missing one critical parameter, power used, and inrush current when power is applied.
          For a standard wall connected power supply this isn’t a problem.
          However I want to take samples every 15minutes and I want it to be off most of the time – so I need an electronic switch in there.
          I started by experimenting with a simple boost circuit, and its tripped me up.
          The core experiment was taking a “SUNKEE LM2577 DC-DC” I found on amazon – a 5V to 12V boost max@2.5A board (inputrange 4-34,output4-35V), and tying the input to USB +5V switch circuit on the Olimex-H407 board, and the output to the transducer power supply. The Olimex-H407 5V switcher device MP1482DS seemed to be pretty hefty at somewhere around 2A.
          I soldered wires to the SUNKEE LM2577 to the H407 USB +5V, and soldered wires to an RJ11 male, and RJ11 female lead to the transducers power/data.
          I put a volt meter on the output of the SUNKEE LM2577 adjusted the output to +12V, and left the meter monitoring its voltaage
          The power supply supplying H407 was slightly above the minimium of +7V, initially taking about 40mA

          Then plugged the transducers RJ11s together.

          It failed to work!.
          As I poked around with a scope I was seeing some of the issues with power supply impedance.
          On plugging in the +12V dropped to +7V, and then USB +5V dropped to +3V.

          I repeated, and monitored the wall supply which kept constant voltage but jumped from 40mA to about 160mA, however it fleeting showed +250mA.
          Looking at the switching waveforms on the MP1482DS it wasn’t coping for some reason, so the output was dropping to +3V, which was probably causing the output SUNKEE to droop to +7V – but taking a lot of current in the process.It seems like the MP1482/inductor should have been able to supply at least 1A, but it wasn’t.
          I modified the powering, connecting the SUNKEE directly to +5V wall supply, with a current meter.
          Hey presto it worked. Watching the +5V wall powersupply, it showed +650mA pulse on plugging in.
          While I don’t believe the powersupply’s has a reliable max pulse indication, I did guess that the +5V circuit source is a lower impedance- and so as this was a quick and dirty experiment. It took me less time to do it, than write it up here.
          So back to the drawing board.
          Generally, in the past for this type of boost powering, what I do is turn on the boost, allow it to power up and fill its output capacitor sufficiently, and then have an electronic switch that switches the steady boosted power directly into the transducer.
          If I have an inrush current problem – generally a seat of the pants estimation – I can boost the output capacitor until I solve the problem.
          So in this case, I’ve gone back to amazon to order “SunFounder 2 Channel DC 5V Relay Module” – something that I hope I can make work with 3.3V H407 outputs, and switch the +12Vs.

          For circuit designs I can use lower cost boosters and +12V MOSFET switcher.

          in reply to: Modbus/12V to cellular #1817
          neilh20
          Participant

            Great. If you want cct comments I’d be happy to participate. I’ve used LM2623 +5V/1A, and also can do +12V

            in reply to: Purchasing Accessory Boards #1782
            neilh20
            Participant

              Hi ChanCafun, nice pics of your system.
              Which Level Troll are you using? Have you had any deployed for any period of time. I’m currently working with Level Troll 500.
              I’m also looking at the RS485. The real issue is the power management, and generating a switched +12V that is typically required in a RS485 level-troll or Keller Nano-level, oh, and of course doing it off a Li-Ion or its more enviro friendly cousin LiFePO4 battery.
              regards.

              in reply to: Simatic iot2020; useful for low-cost monitoring? #1781
              neilh20
              Participant

                Thanks for posting. What comes across is its IP20 – ;
                A rating of “IP20” (pronounced “IP two zero,” not “IP twenty”), denotes protection from solid objects approximately 12mm in size, such as adult fingers; however, it also denotes no protection at all against liquids.

                The other issue is that its an Intel Intel Quark® x1000, 512 MB RAM, 1 Ethernet interface – historically Intel is an electric power hog, but that is all dependent on your location.

                I take its target market to requiring power available (Intel Quark), an Industrial setting with the DIN rail.
                For hot outdoor application, I would think you would want local solar/battery powering and IP62 (or higher eg IP65)- which would be protection from ants/insects and heavy rain failing
                https://en.wikipedia.org/wiki/IP_Code

                in reply to: Cellular telemetry for remote locations #1727
                neilh20
                Participant

                  Wow – congratulations on deploying. Always a watershed moment to get it in to the real outdoors.
                  When its easy, it would be fascinating to see the basic parts list, outdoor configuration, power configuration especially with the GPRSbee, and target sensor data collection
                  Many thanks for sharing.

                  in reply to: Modbus/12V to cellular #1701
                  neilh20
                  Participant

                    Well I’ve done some design thinking on this. I’ve focused on just generating the +12V. The issue with the Mayfly circuit is that the switched pwr comes from the 3.3V which also powers the processor – and a power hog on the 3.3V_Sw is going to cause a processor power glitch – yes I’ve had them in the past and they are nasty to debug 🙂
                    So I want to generate +12V, and possibly the easy way to do it is with
                    SUNKEE LM2577 DC-DC Adjustable Step-up Power Converter – available on Amazon.com (amazing)
                    The design needed for the boost circuit is to be able to switch it on when needed.
                    The +5V boost NCP1402 does have an enable on it but it is permanently enabled. It is tied to the 3_3VSw – which is powered by the LDO SPX3819 which is rated for 0.5A.
                    So not very power efficient, drop input voltage (LiPo 4.2V or +5V) to 3.3V and then boost to +5V – but workable
                    The NCP1402 is rated for 130mA, so that is not likely to cause a glitch on the 3.3V
                    Ideally I would
                    cut trace to C13/L1 and tie power line to C7/D3
                    Then the NCP1402 U3-En SJ5-3 cut & strapped to Port-D22/(3.3_SW) OR another Port

                    So I wonder it the layout for the Mayfly is easily available to see how the traces are done.

                    I’ve ordered the $6 SUNKEE LM2577 DC-DC Adjustable Step-up Power Converter and a Mayfly to try it out.

                    The other option I considered was to use +12V -start with a SLC battery, and then drop the voltage to +5V for Mayfly.
                    All the switching is done at 12V/SLA low impedance, with an interesting
                    $15 CWE Arduino Dual Channel Smart FET Driver Board with Current Sensing 8-28VDC
                    and a switch converter 12Vto +5V for mayfly.
                    Theoretically it would have been then possible to add +5V/1A cellular phone later – but this would get expensive for power modules and take more design now.

                    One of the reasons I considered +12V is I am using an Olimex-STM32-H407 – which takes +12V, for prototyping modbusm.
                    Personally I think the STM32F4 family is going to provide a lot of versatility for the future –
                    http://www.stm32duino.com/ for a lot of small boards now and

                    Arduino STAR Otto features STM32, multimedia, WiFi

                    The key is a rugged mechanical environmental enclosure, solar power, power switching managed by the SMT32F4xx, and low power sleep capability, and using its unique USB Host capability for pluggable USB modems. This can then communicate with the Mayfly over the XbeePro modules. So that’s the longer term plan.

                    in reply to: Precise analog voltage measurement using Arduino #1579
                    neilh20
                    Participant

                      Hey Goodluck
                      Sounds like you have got the measurement traceability going. The local water company here installed a German ultrasonic meter, on the recommendation of Siemens. So far it seems to be slightly under-reading the water flow compared to the impeller meter I have, but haven’t done any detailed measurements on it. I’m waiting to see if there will be any visibility of the readings to customers (me).
                      I’m using 12V and 4-20mA on a project. Its a using the commercial Onset U30-C3G with analog interface and reporting in over cellular. It has a WiFi option.
                      The 4-20mA interface has been very good, accurate and stable signal across the 12bit ADC.
                      I first tested it with some resistors to see how stable it is.

                      Our issue was accuracy – we wanted to measure changes of 1/100′ or 0.01′. That limited the dynamic range to 10′ depth of water.
                      So technically the dynamic range is about 10bit- 2**10=1024. Then you need to take into account digital quantization – the accuracy of the ADC and potential slight drifts that can occur. Temperature drift also needed to be accounted for, and potentially there can be a 20C change in temperature across a day/24hr cycle.
                      I enclose a graph taken from a snapshot of two sensors tied together over 24hrs of pre-deployment testing in a stable 3.6′ water column. Typically I tested in 0.5′ of water, but wanted to test them at different depth. I believe the noise is coming from the sensors – both sensors are the same type of depth gage, but different responses.
                      The graph demonstrates the value in doing some acceptance testing in known conditions – in this case level water (except for slight evaporation).
                      You may want to consider how you can generate a 1/16 gallon flow/leak and then monitor the meters over a couple of weeks.

                      Attachments:
                      in reply to: Precise analog voltage measurement using Arduino #1575
                      neilh20
                      Participant

                        Hi Jeff, I think you’ve taken on a difficult challenge with estimating what is exactly ‘0’ at 4mA, and you would want to look at what is a theoritical low flow and can your ADC even detect that.
                        Just wondering what the history is with having a 4-20mA flow detector in this location.
                        Just to compare it against something I’ve done, for monitoring and leak detection I’ve used a water meter with a gallon clicker – Jerman.com DLJSJ75C.
                        So every time a gallon passes it closes/releases a relay. Then I have an Arduino SAM3X that measures the clicks. I could publish the code on that if you are interested.
                        It sends the results to thingspeak – I can then read the data from thingspeak and create a graph. I attach a graph – the blue is the water used on the house water meter, and the black line is the garden water meter.
                        For leak detection – this is guaranteed to show every gallon and the way I do it is to count over 15minutes.
                        The actual reed relay closes/opens on 0.1G passing and stays open for the next 0.9G – so technically it would be possible to detect a continuous leak down to 0.1G over some period.

                        The basic issue with looking for leaks at 4ma/ is that the trace ability of the measurements is challenging.
                        On the 4-20mA side its how accurate is the 4mA to indicate low flow, and how you integrate it, and on your Uno side how accurate is the Vref and how much accuracy can you get from the ADC digitization.
                        I personally stay away from anything that hasn’t got at least 12bits on the ADC and a good ADC ref. The Mayfly has a good analog monitoring – see its specs. Then you need to understand your analog flow meters and come up with a definition of what is the leak flow rate that you want to catch.

                        So the 4-20mA is useful for communicating over wires over a long distance, and for interfacing to specific types of monitoring equipment.

                        Sorry to not be more helpful on 4-20mA, but hope the reasoning is visible.

                      Viewing 10 posts - 341 through 350 (of 371 total)