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  • Mark posted an update in the group Sensor Developers 2 years, 4 months ago

    Does anyone have any experience with these 24v 4-20ma depth sensors from China?
    https://www.amazon.com/4-20mA-Submersible-Transmitter-Pressure-Transducer/dp/B07F5BF248
    I have a few and they seem well constructed. We are working on integrating them with the Mayfly.
    This requires A) a 24 volt voltage source. (We are trying https://www.amazon.com/QEBIDUL-Converter-Step-down-Regulator-Stabilizer/dp/B07BTHSK8H/ref=sr_1_5?keywords=5-30+volt+dc+to+dc+converter&qid=1564408261&s=industrial&sr=1-5) and B) some input components to measure the current and protect against over voltages. Any recommendations would be appreciated.

    • Hi Mark
      Thanks for sharing – just wondering what your power supply source is. Are you solar powered, running of the LiIon battery or another source.
      Technically the spec says “Power Supply:12~36VDC” – that is nominally 24V, but actually a range. That would fit with the https://github.com/EnviroDIY/SensorModbusMaster/tree/master/hardware/Modbus-Mayfly_WingShield
      If you really need the 24V then there is a step up regulator U3V50F24

      The RS485 SOM specified in the Modbus-Mayfly_WingShield does have some protection on it – but the PCB traces are weak for the protect diodes return path to a ground. It would be simple to add a straight wire to beef up that and use the RS485 SOM .

      Have you found the manual specifying the Qidian QD-130 sensors registers to see if they are compatible one of the Maylfy RS485 sensors.

      • Thanks for the great information. I will look into these items and get back.

      • We are planning to be solar powered using a 2500 mAh 3.7V battery and Voltaic Systems 2W/6V solar panel

        • It sounds like the RS485 Wing Shield would work for you, probably standard voltage option but you should check it works. It does require assembly and soldering.
          I was wondering if you have the sensor manual including data protocol and what RS485 registers,

          • No manual. Just a data sheet I can’t read

            • Hello Mark – oops I’m thinking in another dual world – my brain fart.
              The sensor is 4-20mA (i’m using that type of sensor in non-mayfly Onset U30 loggers and trying to move to Mayfly/RS485).
              The 4-20mA with excitation 12-36V is much simpler, but it is not supported directly by Mayfly.
              The excitation voltage can be done with the switched voltage booster portion of the RS485 board, and a current measurement device calibrated for the 20mA. Let me think about it and post back here
              How many are you looking for?,
              How willing/experienced are you to a) solder build boards and
              b) compile a software Mayfly build
              c) how are you looking to log the readings 1) SD card 2) WiFi to [data.envirodiy.org or..] 3) Celllar or …

            • We are expecting to do a little soldering and working on the Mayfly sketch. The data will be sent via Wifi to our own server and to EnvironDIY

    • So to restart the thread – it can be done with RS485 wing board to generate a switched excitation voltage (from the LiIon). The voltage probably needs to be 14V+ so could be U3V50F24 to generate 24V.
      To measure the 4-20mA accurately use Adafruit INA219 with a 10ohm resistor.
      https://www.adafruit.com/product/904
      The Mayfly has the INA219 drivers, I submitted them, but they are a version of the Adafruit drivers.
      It probably makes sense to create a version of the INA219 driver as a 4-20mA sensor with switched excitation. The resistor could be an option to the driver, and for 10ohms a 20mA FullScaleReading, would be 0.2V. The INA219 measures voltage to 0.32Vs, and this would be calibrated to produce a mA measurement.
      I would recommend a 10ohm YR1B10RCC -$0.62 (accurate 0.1% with a low temperature drift 50ppm/C) https://www.digikey.com/product-detail/en/te-connectivity-passive-product/YR1B10RCC/A105944CT-ND/3477513