The Vernier Breadboard Cables (Breadboard Cable (Analog) (BB-BTA) and Breadboard Cable (Digital) (BB-BTD)) provide an easy way to connect your sensor to a Vernier interface. Once your sensor is connected to an interface, you can use Logger Pro to calibrate the sensor and collect and analyze data. (Note: Graphical Analysis and Graphical Analysis Pro doe not allow for manual setup of sensors and thus cannot collect data from a homemade sensor.)
Use the Vernier Breadboard Cable to connect to a Vernier Interface
The Vernier Breadboard Cable connects to a standard electronics prototyping board and provides the following lines:
A Vernier interface, such as a LabQuest 2 or LabQuest Mini, can read sensor output signals on two different ranges: 0-5 V or +/- 10 V. The output of your sensor dictates the lines to which you should connect your sensor. The following are a few of the common cases for homemade sensors:
|Sensor Output Signal||How to Connect to Breadboard Cable|
|Analog Voltage: 0-5 V||Connect the sensor output to SIG1 and your sensor’s ground terminal to GND of an Analog Breadboard Cable.|
|Analog Voltage: +/-10 V||Connect the sensor output to SIG2 and your sensor’s ground terminal to GND of an Analog Breadboard Cable.|
|Analog Voltage: milli-volt range||Very small voltages, such as those from a Wheatstone bridge, are most easily read into a Vernier interface via the Instrumentation Amplifier (INA-BTA), rather than a Breadboard Cable. The Instrumentation Amplifier monitors voltages from 20 mV to 1 V (DC or AC). It has several switch settings to allow you to select the best gain and includes auto-ID functionality for each of the six ranges. The Strain Gage Measurement Project from Engineering Projects with NI LabVIEW and Vernier (EPV, discontinued) is an excellent example of using the Instrumentation Amplifier to input a very small voltage signal into Logger Pro.|
|Variable resistance||If your sensor uses a variable resistor, such as a thermistor or photoresistor, a voltage divider is a convenient way to convert the change in resistance into a change in voltage.
A voltage divider places a known resistance (R1) and a variable resistor (RT) in series across a known voltage (Vin). The signal output voltage (Vout) can be measured across the variable resistor. The value of the upper resistor, R1, will determine the range (or swing) of the sensor’s output voltage, Vout. R1 should be larger than the variable resistor’s minimum resistance, but smaller than the variable resistor’s maximum resistance.Any power source can be used for Vin, but the 5V line from the breadboard cable is convenient and will produce Vout measurements between 0 and 5 V. For example, in the Building a Temperature Sensor project in Engineering Projects with NI LabVIEW and Vernier (EPV, discontinued), the thermistor is wired to the Breadboard Cable in this manner:
|Digital Voltage||If your sensor produces a simple “high” voltage or “low” voltage in response to changes in the measurement, you will use the Digital Breadboard Cable. How Logger Pro interprets the input values it reads depends on what you identify the sensor as, e.g. a motion detector, photogate, radiation monitor, or rotary motion sensor. See a detailed pin out diagram for each mode here. This photogate project is a good example of homemade digital sensor.|
Calibrate Your Sensor in Logger Pro
After connecting the sensor and interface, calibrate your sensor.
1. Connect the Breadboard Cable to CH1 or DIG/SONIC1 of your interface and connect your interface to the computer.
2. Start Logger Pro.
3. Choose Set Up Sensors from the Experiment menu. To continue, follow the directions below for the type of sensor your are using.
4. In the CH1 list, select Choose Sensor. From the Voltage list, select Raw Voltage (0-5 V) or Raw Voltage (-/+10 V), depending on which voltage range is most appropriate for your sensor. Note: At this point, sensor output values will be displayed in the digital meter.
5. Create a calculated column to perform the calibration. The calibration equation you enter into the Expression field depends on the nature of your sensor.
A simple linear calibration can be found by measuring the maximum and minimum voltage, Vmax and Vmin respectively, produced by the sensor under the conditions in which it will be typically used. In the Expression field, enter: (“Potential”-Vmin)/(Vmax-Vmin)
4. In the DIG/SONIC1 list, select Choose Sensor. Select the digital device that is most appropriate for your sensor. If you select “Photogate”, you will need to specify which timing mode to use.
Collect and Analyze Data
Now that your homemade sensor is connected to Logger Pro and its output signal is calibrated, you can begin data collection just as you would with any Vernier sensor.