So it can be done, I’ve now able to read a Seneye USB device using my own server and Python code. You can read about the first couple of steps here and here. The process was difficult due to a number of quirks and barriers:

• the Seneye code uses a C++ STRUCT for data mapping, implying byte-alignment for different data types and bit padding
• the SUD holds local data readings until it is able to reconnect to the cloud, and will fill up to capacity if it is not connected to the cloud
• values are decimal-shifted for display
• if any errors occur the device seems to enter a timeout-locked state (perhaps by missing the BYESUD message?) and has to be unplugged

Firstly the official Seneye C++ code as compiled on my machine and reading the reference mug of water:

Then the output from the Seneye code, without their lovely ASCII logo art:

  Device: LSDF0982LSDFOSDLJKS9E89S0D9SDMF v.2.0.16  Type:  Home
  Temperature (C)   │ 20.375                      Is Kelvin           │                   ┌────┘ └────┐
  pH                │ 7.94                        Kelvin              │                   │ ┌─┐   ┌─┐ │
  NH3 (ppm)         │ 0.02                        PAR                 │                   │ └─┘   └─┘ │
  In Water          │ True                        LUX                 │                   │           │
  Slide NOT fitted  │ False                       PUR                 │                   │   ┌───┐   │
  Slide Expired     │ False                                           │                   │   │   │   │
  Press R for reading, 1-5 to change LED, Q to quit

Taking this and observing that the pH value was 7.94, which is 031a in hex, I  scanned through the printed hex dump (and I really must write a small routine to dump binary, hex, and offset in bytes-per-line).  The latest output from my code with debugging turned on can be seen below.

('device       >>>', )
('configuration>>>', )
('interface    >>>', )
('endpoint in  >>>', )
('endpoint out >>>', )
('HELO ret code>>>', 8)
('HELO hex     >>>', (<type 'array.array'>, 64, '88:01:01:01:30:4e:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00'))
('READ ret code>>>', 7)
('sensor hex   >>>', (<type 'array.array'>, 64, '00:01:57:59:59:59:05:00:00:00:1a:03:10:00:1a:4f:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00'))
('sensor bits len>', 512)
('sensor bits  >>>', '00000000000000010101011101011001010110010101100100000101000000000000000000000000000110100000001100010000000000000001101001001111000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000')
('BYE ret code >>>', 6)
{'InWater': True,
 'NH3': 0,
 'SlideExpired': False,
 'SlideNotFitted': False,
 'Temp': 20,
 'pH': 7}

This means that the pH starts at position 80, runs for two bytes, and is little endian (so x031a is the equivalent of 794 in decimal, and packed into two bytes as it is a short means it looks like ‘1a.03’. The 7.94 comes about because certain of the values returned are divided by 1000, certain ones by 100. It helps to read and understand the Seneye C++ code.

There is obviously some extra commands that are sent by the Seneye Connect software, plus I believe some cryptographic hashes in operation to ensure devices update, only upload from authorised accounts, and other things to keep the Seneye ecosystem together.

Conclusion

This means that it is unlikely that home DIYers will be able to replicate the full Seneye Connect experience. A LattePanda running Windows 10 and the Seneye Connect software or Seneye SWS probably still give the best experience, along with SMS text alerts and the Seneye dashboard. However, for those who are willing to tinker with code this project provides a reasonable solution.

In my previous post I discussed how to discover information about the Seneye device, here I will describe some simple code to read values from it and push these to a MQTT broker. I have this running on a small Raspberry Pi Zero W, on which I also have the Motion software and a small streaming web cam.

Having got lots of good information from the Linux commands you start by finding if the device is attached:

    dev = usb.core.find(idVendor=9463, idProduct=8708)

Next, ensure that the operating system does not have control of the device:

    interface = 0
    if dev.is_kernel_driver_active(interface) is True:
        kernel_driver_active = True
        dev.detach_kernel_driver(interface)

Then set the first configuration and claim the interface – and it needs to be done in that order, apparently!

dev.set_configuration()
usb.util.claim_interface(dev, interface)
cfg = dev.get_active_configuration()
intf = cfg[(0,0)]

Alternate settings may be ignored as most devices do not have them, so we move straight to the endpoint and search for the first in/out.

epIn = usb.util.find_descriptor(interface, custom_match= lambda e: usb.util.endpoint_direction(e.bEndpointAddress) == usb.util.ENDPOINT_IN)
epOut = usb.util.find_descriptor(interface, custom_match = lambda e: usb.util.endpoint_direction(e.bEndpointAddress) == usb.util.ENDPOINT_OUT)

Then send the READING message to the device, read the response, and read again with longer timeout so that the measurements can be read and returned.

    msg="READING"
    rc=dev.write(epOut,msg)
    ret=dev.read(epIn,epIn.wMaxPacketSize,1000)
    ret=dev.read(epIn,epIn.wMaxPacketSize,10000)

Once done the fun of picking the bit flags and integers out of the results starts and I have provided just six of them, as they were the ones I could confirm from the Seneye C++ program. At the end you need to send a closing message called “BYESUD”, I guess to tell the device to go into sleep mode or whatever.

    msg="BYESUD"
    rc=dev.write(epOut,msg)

Finished code

All this code is available in my GitHub repository and I’d encourage you to read the code, try it on one of your systems, and if you want to improve it fork the repo and submit pull requests to me. I’m not looking to make it complex with control functions and displays, just something simple and lightweight.

I recently purchased the excellent Seneye aquarium monitor. It is a small device with that sits in a fish tank and monitors various parameters.

I’d been looking for a simple device like this for some time – not too complex, not too expensive. It may not sense some parameters needed in a marine tank however it does do the basics such as temperature, in/out of water, ammonia and pH. As I mentioned before, water chemistry is difficult and you shouldn’t knock those who have tried. Other devices are more complex, expensive, or actually never successfully made it to market. In essence it reads the colour change of a litmus strip by comparing it to a sealed reference, as well as temperature and water refraction.

The challenge came about because although they have a cloud solution that transmits readings every 30 minutes, the device itself has to connect to a Windows PC and thence to the cloud. I’d looked at running a low-powered Windows SBC or even purchasing Seneye’s always-on connection device, but the easiest seemed to be to read the USB device.

USB devices

USB devices are a wonder to behold. They do a lot of work internally and the USB protocol spec runs for many pages. I looked for libraries to help me read the device and found a couple which work in Python, my language of choice. USB also delineates a special form of device known as the ‘HID’, or Human Interface Device. These are things such as USB mice, track-pads and keyboards. They have a simpler interface and only use a couple of the modes of transfer: control, and interrupt.

Walking the USB tree

As USB devices have a hierarchical protocol we need to find out some things about it.

1. Device
2. Configuration
3. Interface
4. Alternate setting
5. Endpoint

We start by looking at the device itself using Linux commands and the udevadm command. The udevadm command may not be installed on your system and should be installed using your distro’s package manager.

Firstly, using lsusb we get to see where our device is sitting on the bus – and note that this changes every time we plug it in.

lsusb
Bus 002 Device 089: ID 24f7:2204

… so our device is on the bus number 2, and is at device number 89. Now, using udevadm we can test this and get the device characteristics:

udevadm info -a -p $(udevadm info -q path -n /dev/bus/usb/002/089)
looking at device '/devices/pci0000:00/0000:00:14.0/usb2/2-1':
    KERNEL=="2-1"
    SUBSYSTEM=="usb"
    DRIVER=="usb"
    ATTR{authorized}=="1"
    ATTR{avoid_reset_quirk}=="0"
    ATTR{bConfigurationValue}=="1"
    ATTR{bDeviceClass}=="00"
    ATTR{bDeviceProtocol}=="02"
    ATTR{bDeviceSubClass}=="00"
    ATTR{bMaxPacketSize0}=="64"
    ATTR{bMaxPower}=="250mA"
    ATTR{bNumConfigurations}=="1"
    ATTR{bNumInterfaces}==" 1"
    ATTR{bcdDevice}=="0125"
    ATTR{bmAttributes}=="80"
    ATTR{busnum}=="2"
    ATTR{configuration}==""
    ATTR{devnum}=="89"
    ATTR{devpath}=="1"
    ATTR{idProduct}=="2204"
    ATTR{idVendor}=="24f7"
    ATTR{ltm_capable}=="no"
    ATTR{manufacturer}=="Seneye ltd"
    ATTR{maxchild}=="0"
    ATTR{product}=="Seneye SUD v 2.0.16"
    ATTR{quirks}=="0x0"
    ATTR{removable}=="removable"
    ATTR{serial}=="F500214755881923AEAEA4260100D020"
    ATTR{speed}=="12"
    ATTR{urbnum}=="32"
    ATTR{version}==" 2.00"

From this we can see that the device has one configuration and one interface. It also contains the device’s serial number. Other notable things are the maximum packet size, and the power requirements. That number of interfaces response is a little odd?

On the trail for my aquarium monitor I came across the excellent Seneye range of aquarium sensors. They seem to provide all that I need:

• Acidity (pH) reading
• Temperature
• Light
• Ammonia (NH₃)

… and are USB connected and powered. So far so good. They seem to use a replaceable litmus test strip which is read by what appears to be a colour-detecting LDR, so I understand the need to replace them periodically to maintain calibration and readings. What is a little frustrating is that the software only runs on Windows.

Now, I think Windows is a capable OS and useful in a variety of contexts, but one of those isn’t the area of small and embedded devices. These have very limited memory models and typically require ultra-low power levels when sleeping – something I’m certain that Windows doesn’t really understand. To run Windows locally I could actually buy a LattePanda board with Windows 10 IOT, but at around £100 the sticker shock has set in and I am thinking of taking another route.

Off-the Shelf Devices

I think I have two options at this point: Continue with the Seneye and try to get their SUD Driver working on a Linux box, or roll my own:

Seneye and SUD driver

Temperature and light are fairly easy to get with sensors like the DS18B20 and light-detecting diodes (LDRs). So, the extra which the Seneye solution give are the pH reading (which isn’t easy to calibrate nor leave in a solution too long) and the ammonia. I appreciate that these are difficult things for the reasons below.

Roll my own

What I’d ideally like is a single-board computer that is tiny, runs off a battery forever, reads from the sensors outlined above, and can communicate to a local WiFi access point. The rest I can do myself including piping MQTT messages to a remote server, setting up a firewall and whatnot. I think all of this could conceivably almost fit onto a ESP8266 device, but the voltage handling for the pH probe would most likely not go too well, and I don’t know about the inputs for the temperature probe. Measuring the chemicals is way more difficult, until they are solved in a way which means that fouling of the sensor or leaching of the indicator dyes does not occur, I think I will let others do the pathfinding.

So it is likely that something more capable like at least a WiPy or RasPi Zero W would work, or even larger like a full-blown Odroid C2 or RaspPi 3. But why stop there? Why not just go full LattePanda and £100 if you need those, since they really don’t run well on batteries.

Chemistry – measuring soup

What I really need is a neat, innovative way to read water chemistry. My son who is a chemistry student at university tells me that lab equipment to measure individual molecules is terribly expensive, and that mostly they are used in a pure environment where only one type of molecule is present in a solution. What I need is a way to look in a non-invasive way at ‘soup’, and tell how much of one chemical it contains.

Not easy.

This is likely the reason many of these devices either use rare earth metals and fancy rotating face-plates to discourage fouling. They still need replacing every so often because they are in the aquarium water, and the dyes and inks are leaching away. The Seneye does this with a covered, reference litmus strip while another is exposed to the aquarium water and provides the measurements.

Spectroscopy

My son spoke of IR-spectroscopy which is used in organic chemistry, and UV-spectroscopy which is used elsewhere. IR-spectroscopy is likely what devices like the Mindstream are using, comparing reference ranges with that coming back from their IR LDRs and using clever materials and rotation to avoid excessive fouling. It is likely that measuring such a chaotic solution would mean that multiple wave lengths would be returned, however if you just wanted very coarse-grained information like ‘no ammonia/ammonia’ it may be possible.

My guess is that these real-world issues have hampered a single device that tells you what is in your aquarium water for some time, and that until some clever thinking is applied or new material science used, we will have to continue either replacing our litmus strips periodically or buying expensive reference disks.