Craftbeerpi3 sensor for measuring ph values. Using the ADS115 A/D via I2C connection

1. Ensure you have activated the I2C connection in the Raspi Configurations:

2. Load the PHMeasureADS1115 addin from the CraftbeerPi3 addin section.

   Just if you need a workaround:

   Key in in the command box of Raspi

   git clone https://github.com/JamFfm/PHMeasureADS1115.git -b master --single-branch /home/pi/craftbeerpi3/modules/plugins/PHMeasureADS1115

3. Reboot at least CBPi3

The pH has got an influence on the beer taste. Please inform yourself in the literature. Usually the mash will be between 4.5pH and 5.8pH.

The target pH for the mash usually should be between 5.3pH and 5.7pH

Therefore it is important to know the pH of the mash.

German link to ph in Beer

• https://www.maischemalzundmehr.de/index.php?inhaltmitte=exp_maischph

• Works much more stable/precise like the MCP3008 IC Module.
• I2C connection is very easy to handle.
• The driver is build in. No need to install software modules.
• This is the supposed ADS on the CBPi Extentionboard 3 (just solder ADS, Levelshifter and connect probe board with screwterminals)

at ebay

• https://www.ebay.de/i/322935814230?ul_noapp=true

but there are same in Aliexpress. Search for this: "Liquid PH Value Erkennung Detect Modul +BNC Electrode Probe for Arduino"

The probe board is an analog sensor. RaspberryPi can read only digital sensors. Therefore you need an analog/digital converter like the ADS1115 (16Bit)

To connect the ADS1115 to the Raspberry Pi use the following connections:

• ADS GND to RASPI GND
• ADS VDD to RASPI 5v
• ADS SCL to RASPI SCL (daisychain possible), put a level shifter 5v/3.3v inbetween because the Raspi pins can only stand 3.3v
• ADS SCA to RASPI SCA (daisychain possible), put a level shifter 5v/3.3v inbetween
• Address have a look at the specs of ADS1115 for changing adress, put a level shifter 5v/3.3v inbetween
• Alert have a look at the specs of ADS1115 for Alert events, put a level shifter 5v/3.3v inbetween
• A0 to Po of the PhMeasure Board.

Please have a look here:

http://www.netzmafia.de/skripten/hardware/RasPi/Projekt-ADS1115/index.html

• BNC plug: Where you put the probe. It seems to work with any probe with a calibration difference.

• Pin To: Should be the temperature but I can't make it works.

• Pin Do: High/Low 3.3v adjustable limit.

• Pin G/GND: Probe ground. It may be useful when the ground is not the same as your Raspi. In fact I use the ground of the Raspi. In some circumstances the ground voltage of the liquid to measure can be different.

• Pin G/GND: Power ground (ex. Raspi).

• Pin V+/VCC: Input power 5V DC (direct from Raspi).

• Blue potentiometer close to BNC: pH offset.

• Blue potentiometer close to pins: limit adjustment.

• Black component with 103 printed (not the one between potentiometers): thermistor for temperature compensation.

The ADS 1115 has got 16Bit precision.

16 Bit = 32767 possible values between 0V and Gain maxV and 32767 possible values between -Gain maxV and 0V. We assume there is a voltage measure at shortcut and second at measuring pH 4.01 buffer. See below at end of this text for more explinations.

With gain 1 (+-4.096V)

voltage = measure * 4.096 / 32768 ; //classic digital to voltage conversion

PH_step = (voltage@PH7 - [email protected]) / (PH7 - PH4.01) = (2.5-3.05) / (7-4.01) = (-.55/2.99) = -0.1839....

PH_probe = PH7 - ((voltage@PH7 - voltage@probe) / PH_step)

phvalue = 7 + ((2.5 - voltage) / 0.1839 )

There is a very small script to determine the Factor and the formula:

• Put a voltmeter to measure the voltage between GND and Po to measure voltage.
• You need the measured voltage while producing a shortcut between inner pole and outer area of the BNC of the probeboard.
• You need the measured voltage when measuring the buffer pH 4.01
• in the commandbox keyin the following:

cd /home/pi/craftbeerpi3/modules/plugins/PHMeasureADS1115

python calibration.py or as Gui based script doing exactly the same: python GuiCalibration.py

• Follow instructions

• Follow Usage

Use this sensor as any other sensor in Craftbeerpi 3. The Digit and Voltage values can help to calibrate. They are not needed for pH measurement. The main calibaration is already described above and more precise at he end of this file.

Keep in mind that it takes several minutes to get the right pH value.

When using in the rotating mash no stable values are shown but in a probe of mash (ex. a glass) it is stable. My measured Values matched with a other pH measurement tools.

Please do changes of the formula in the code of the file init.py. It is situated in the folder

/home/pi/craftbeerpi3/modules/plugins/PHMeasureADS1115/

According the parameters of the probe it can be situated in max 80°C liquid but not for longtime. I never tryed that until now.

Text as You want. Mybe like "pH Sensor".

Name of the pH Sensor Modul: PHSensorADS1x15

this is the I2C address of the ADS module. Default ist 0x48. If there are two or more modules with the same address you can choose a different address. This means you have to solder connections in a different way. Have a look in the ADS1x15-datasheed. This parameter is rarely used. So in most cases entering 0x48 will do it.

this is the channel you want to read. There are up to 4 channels called A0-A3. You have to connect the sensor to one of the channels.

this is the amplifier of the ADS module. These are the selectable ranges:

For example: Choose a gain of 1 for reading voltages from 0 to 4.09V (ok it is -4.096V to +4.096V bit negative values are scipped for now :-)). Gain 1 will be the right parameter for the pH probe.

Or pick a different gain to change the range of voltages that are read:

• 2/3 = +/-6.144V we use 0 for this range
• 1 = +/-4.096V
• 2 = +/-2.048V
• 4 = +/-1.024V
• 8 = +/-0.512V
• 16 = +/-0.256V

See table 3 in the ADS1015/ADS1115 datasheet for more info on gain.

If you have no idea enter 1

• Digit:
  This shows the value of the MCP 3008 and runs from 0-1024. This is the basic of all measurement.

• Voltage: This shows the calculated value of the Voltage measurement. It depends on the Gain selected.

  Example: Gain 1 = +/-4.096V

  Voltage = ((4.096V * Digit) / 32767) - offset

  This means 32767 digit is equal to 4.096V.

  Why only 32767? Because there are another 32767 values of the negative numbers. But we only deal with the positive number range.

  Check it by this: Put a voltmeter to measure the voltage between GND and Po. PH ist calculated by voltage so it should be checked with voltmeter.

• pH Value: This shows the calculated value of the pH measurment.

  phvalue = 7 + ((2.532V - measured_voltage) / 0.1839 )

  As discribed above (calibration) the 0.1839 has to be adopted in the code. You may need a different factor. So this one is always individual

  Example I used (7 + ((2.548V - measured_voltage) / 0.17826))

  Maybe the 2.532V (or 2.548V) has to be adopted to the voltage value you measure with the short circuit between the the small BNC hole and the external part of BNC. The voltage of short circuit is the aquivelent to pH 7.

You can easily change the addon for different analog sensors.

There are only some lines to change.

I use the ADS115 in a CraftBeerPi Extensionboard 3 in combination with a livel shifter

• You have to find out the right parameter to show the right voltage values and the right pH values
• When using in the rotating mash no stable values are shown
• Wrong spelling
• no temperature calibration, buffer ist calibrated to 25°C, so probes should also habe 25°C
• I bought 3 probes. Only one shows stable values. One is useless and one shows fairly credible values.

Report issues either in this Git section or at Facebook at the Craftbeerpi group

I got all my knowledge from these links:

• http://www.netzmafia.de/skripten/hardware/RasPi/Projekt-ADS1115/index.html

  Used this for the libs and classes

• https://forum.arduino.cc/index.php?topic=336012.0

  last post first page, for understanding probe in general

• https://www.botshop.co.za/how-to-use-a-ph-probe-and-sensor/

  additional info

• https://raspberrypi.stackexchange.com/questions/96653/calibrate-ph-4502c-ph-meter

The offset is the shifting of all pH values to a specific voltage range. If a pH 7 output a voltage of 2.2v and pH 8 a voltage of 2.1v, then a shift of +0.3v move the pH 7 to 2.5v and the pH 8 to 2.4v.

The offset can be done on the board or via software but it's probably easyer on the board because it's probe independant and there are less programming to do.

Connect GND (both) of the probeboard to Raspi GND and and probeboard Vcc to Raspi 5v. Please use a levelshifter to avoid damage at the GPIO which only support 3.3v.

Remove the probe (disconnect BNC) and do a short circuit between the the small BNC hole and the external part of BNC. Use a wire to do that.

Put a voltmeter to measure the voltage between probeboard GND and probeboard Po. Adjust the pot (close BNC) until the output is nearest to 2.5v.

Now the pH 7 have an exact value of 2.5v (or what you measure) because the probe will output 0 millivolt.

In my case I could only lower voltage to 2.548V.

Now you need one or more buffer solutions depending the range and precision you want. Ideally you should know the range of the measure you want to do with your system.

I use upcoming beer between pH 5 and pH 7. Therefore I choose the buffer 4.01 (and 6.86 to verify). If you usually measure pH between 8 and 10 choose buffer 9.18 (eventually 6.86 to verify).

Connect the (clean) probe and put it in the buffer then let it stabilize for a minute. You know it's stable when it goes up and down (e.x. 3.04 then 3.05 then 3.03 then 3.04). Take note of the voltmeter value. At this Example it comes out at 3.05V at 4.01 pH buffer.

The PH_step calculation is quite simple. You take the difference between the two known voltage, in my example 2.5v@pH7 and [email protected] which is -0.55v.

It's the voltage range equivalent of the pH range from 7 to 4.01, which is 2.99 pH units. A small division of the voltage by pH units gives you a volts per pH number (0,1839... in my case).

The PH_probe is calculated by taking the known pH 7 voltage (2.5v) where we add some PH_step to match the probe voltage. This means that a pH of 8 have a voltage value of 2.5v (pH 7) + 0.1839 (1 unit/step); pH 9 then is 2.5v + 0.1839 + 0.1839 = 2.87v.

To determine the Unit per Step (=PH_step in formula) is important to know.

The ADS 1115 has 16Bit precision.

16 Bit = 32767 possible values between 0V and Gain max V and 32767 possible values between -Gain max V and 0v

With gain 1 (+-4.096V)

voltage = measure * 4.096 / 32768 ; //classic digital to voltage conversion

PH_step = (voltage@PH7 - [email protected]) / (PH7 - PH4.01) = (2.5-3.05) / (7-4.01) = (-.55/2.99) = -0.1839....

PH_probe = PH7 - ((voltage@PH7 - voltage@probe) / PH_step)

phvalue = 7 + ((2.5 - voltage) / 0.1839 )