Accurately Measuring Electrical Conductivity

[Ryan] designed a PCB that lets you easily take readings from a commercial electrical conductivity probe over I2C. Conductivity measurements are great for measuring the salinity of a solution, which is useful for applications like hydroponics. While the probes themselves are a bit pricey (on the order of $50 from eBay), they are very accurate and last a long time.

Commercial conductivity probes contain platinum electrodes to prevent corrosion. The electrodes are excited with an AC signal, which prevents polarization of the solution and avoids chemical reactions at the electrodes. The voltage across the two electrodes is measured while the electrodes are being excited, which is proportional to the conductivity of the solution

[Ryan]’s board generates +/-5v and uses a Wien bridge oscillator to generate a sine wave which excites the outermost electrodes. The voltage across the electrodes is amplified and fed into a MCP3221, an inexpensive 12-bit ADC with an I2C interface. [Ryan] also wrote an Arduino library for the MCP3221 so you can easily get your probe up and running.

 

Collin’s Lab is Coming Back

Collin

We would like to share a bit of good news; Collin’s Lab is back on the airwaves of the Internet. If you didn’t know, [Collin Cunningham] previously created excellent short videos, sometimes entertainingly tongue-in-cheek, for Make Magazines on the subjects of electronic components and fundamental electronics. In 2012 he was hired at Adafruit as a Creative Engineer to help with software development and video production.

Going forward Collin’s Lab videos will be a regular feature on Adafruit’s Blog and their YouTube channel. We’re sure there is going to be tons of entertaining learning from Collin with his unique video production skills and presentation delivery.

This first release of Collin’s Lab on Adafruit is a primer review covering fundamental multimeter functionality and measurements. Not much here for the medium to advanced electronics hacker but for the beginner this is an excellent and quick way to learn the basics on using your multimeter.

If you want to checkout Collin’s older video productions you can find them on his Narbotic Instruments site under – “Make Presents” and “Collin’s Lab” or watch them all with this convenient playlist. Just after the break you can also watch his latest edition of Collin’s Lab.

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Modeling an object with internal IMUs

[Joseph Malloch] sent in a really cool video of him modeling a piece of foam twisting and turning in 3D space.

To translate the twists, bends, and turns of his piece of foam, [Joseph] used several inertial measurement units (IMUs) to track the shape of a deformable object. These IMUs consist of a 3-axis accelerometer, 3-axis gyroscope, and a 3-axis magnetometer to track their movement in 3D space. When these IMUs are placed along a deformable object, the data can be downloaded from a computer and the object can be reconstructed in virtual space.

This project comes from the fruitful minds at the Input Devices and Music Interaction Lab at McGill University in Montreal. While we’re not quite sure how modeled deformable objects could be used in a user interface, what use is a newborn baby? If you’ve got an idea of what this could be used for, drop a note in the comments. Maybe the Power Glove needs an update – an IMU-enabled jumpsuit that would put the Kinect to shame.

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Parts: Analog distance sensors (Sharp GP2D12/2Y0A02)

Sharp GP2D12 and 2Y0A02 infrared rangers output a voltage proportionate to the distance of an object from the sensor.  The GPD12 senses objects at a distance of 10-80cm, while the 2Y0A02 has twice the range.

We’ve previously looked at the Sharp GP2Y0D02 digital proximity sensor. It only signals the presence of objects, while the GP2D12 and 2Y0A02 measure distance to them. If you’ve got a GP2YoD02, it might still be possible to tap the analog output. We’ll show you how use these sensors below.

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