[Farming-Hamilton-IA]

I am interested in seeing if anyone has been able to successfully read OPI cables with an Arduino or other microcontroller. I found an old thread about it, and it looks like folks have been able to get the temperature and relative humidity.

Reading Opi moisture cables with 1wire (one wire)

If you use a resistance sensor, and calibrate it for the density of the grain, you can get far better moisture readings than the sensors in OPI cables. I just read a PhD thesis done a couple of years ago on using small capacitive sensors to measure moisture. They had success, though they never...

www.thecombineforum.com

The main question I have here is how can you get the addresses of the different sensors, and how do you know which level in the cable they are?

Thank you for your ideas. The subscriptions on these cables are just getting very high.

 

[Guy1000]

It is pretty straight forward. The most common sensors used are ds18b20 sensors that use onewire protocol to communicate. Each sensor is connected along a bus and are powered using parasitic power(it robs power off the data line). You can use the arduino onewire library to read them. To get their positions we utilize the two bytes of user programable memory in the sensors(originally intended for temperature alarms) one is the cable is and the other is the sensor position. From their you basically make a sketch that runs through the onewire search algorithm and read the temperature then the bin and sensor numbers and sort them into an array.

Humidity is a little more complicated as you use a DS28EA00 sensor that has 2 io pins on it, and a SHT35 I2C humidity sensor. The DS28EA00 bit bangs out the I2C signal to the humidity sensor and reads it that way. I have still got to make a library for the humidity but all I use is a modified software I2C library.

 

[Farming-Hamilton-IA]

As I have been exploring the sensors used in the OPI cables, it looks like they are using an SHT15 for temp and RH, and this is going into an IC with a code (EA00949a2+) that I can not find anywhere.

• Looking at the datasheet for the SHT15 sensors, it seems to output I2C.
• When looking at the board, the SHT15 is connected to the Mystery IC and then goes onto the 1-wire up to the reader.

Is the Mystery IC the one that "bit bangs" the Temp and RH reading to the 1-wire?

Also, when you mention libraries are you building on the work done by Matt Reimer in this repository?

Read shtxx (relative humidity) attached to ds28ea00 · mattdreimer/[email protected]

Added a function to read relativy humidity from shtxx. See data sheet (https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/Humidity_Sensors/Sensirion_Humidity_Sensors_SHT...

github.com

Thank you for your thoughts.

 

[Guy1000]

Okay. So you have the old style cables. That mystery IC is a DD28EA00. The library’s that I am working on are not Matt Reiner’s but they are for the new style cables that utilize the SHT35 sensors because the sht15 has been discontinued. Is that a 2 wire cable? If so I would bet that that other circuitry is for the parasitic power for the SHT15.

 

[Farming-Hamilton-IA]

Yes, sir, it is a 2-wire with a ground wire and the power/data wire, which is the white one. I got this cable off eBay to take apart, so I am not surprised it is an older version. I am assuming the SHT15 and SHT35 are read and managed in the same way?

Thank you for helping me identify the IC as well that should help. Have you published any work you have done to build a library for the SHT35 version yet? You have made more progress on this than I have so far. Are you using an Arduino in your project?

 

[Guy1000]

The SHT15 doesn’t use I2C but sensirions own protocol and a formula different from the sht35 so they are not compatible. There was actually an update on the commercial readers when they switched the sensors out. I have yet to publish anything at this point as I need to make my code a little better. For my projects I am using a AVR128DB28 with the DxCore add on so I can use the arduino IDE and libraries to program it. It seems to have significantly more functionality and features when compared to other arduinos and is geared specifically for analog signal processing, so it makes it a great microcontroller for driving onewire signals. But nearly any microcontroller will work with the onewire library.

 

[Farming-Hamilton-IA]

What are the core differences you have had to make in your code to read the SHT35? Also, how has OPI labeled the old version differently than the new?

I need to get a new one, and I want to ensure I get the right one.

Looking at the datasheet on the AVR128DB28, I can see why you chose that. It does have a lot more analog capabilities.

 

[torriem]

Why are analog capabilities necessary? With 1-wire everything is digital, even the temperature and humidity values you are reading.

 

[Guy1000]

I am trying to use some of the analog features to improve the reliability of extended onewire networks mainly the comparators(these aren't actually unique to the DB series), and I am using the internal OPAMPS and some of the filtering circuitry(Which might not stay on this path, doesn't seem to be terribly effective). When you start to get large networks there are a lot of weird analog components of the onewire waveform that can begin to manifest(ringing, reflections, EMI). I am trying to use these analog functions of the microcontroller to filter those out. They aren't necessary, but I have seen improvements compared to the basic onewire library when you have poor electrical connections or non-ideal networks, but my main goal is to help with EMI. Plus with the cross-peripheral event system, I can use the hardware peripherals to achieve incredible performance with certain functions that can outperform nearly any other arduino.

 

[Farming-Hamilton-IA]

I am trying to use some of the analog features to improve the reliability of extended onewire networks mainly the comparators(these aren't actually unique to the DB series), and I am using the internal OPAMPS and some of the filtering circuitry(Which might not stay on this path, doesn't seem to be terribly effective). When you start to get large networks there are a lot of weird analog components of the onewire waveform that can begin to manifest(ringing, reflections, EMI). I am trying to use these analog functions of the microcontroller to filter those out. They aren't necessary, but I have seen improvements compared to the basic onewire library when you have poor electrical connections or non-ideal networks, but my main goal is to help with EMI. Plus with the cross-peripheral event system, I can use the hardware peripherals to achieve incredible performance with certain functions that can outperform nearly any other arduino.

What kinds of changes did you make to the 1-wire to bit bang the I2C signal off the SHT35 to something you can read?

 

[Guy1000]

What kinds of changes did you make to the 1-wire to bit bang the I2C signal off the SHT35 to something you can read?

I basically found an example of a software I2C code. Then I replaced all the digitalwrites with the wire commands to write to the DS28EA00’s IO. Then I just looked in the SHT35 data sheet and found the commands I had to send and when to read and punched it in and it all worked. If I get a chance I will post it on my GitHub soon and I will share the link.