This week’s EYE ON NPI (video) will make your sensors soft and luxurious thanks to the Renesas ZSSC3241 Sensor Signal Conditioning IC – which, like a fancy bottle of hair conditioner, will de-tangle any frustrations you have with using resistive sensors that require amplification and filtering.
Many “sensors” that engineers use to measure temperature, pressure, force, light, etc, are actually implemented as resistive sensors. For example, take your common CdS cell also known as an LDR – Light Dependant Resistor. The CdS material has an interesting property that as light shines on it, the resistance decreases.
Another common sensor is the PT100 or PT1000 temperature sensor those are known as RTD – Resistance Temperature Detector – and have a tiny sliver of platinum that has a near-linear increase in resistance as temperature increases. A third example is the classic strain gauge, made of a thin plate of patterned metallic material that very slightly changes resistance as it is deformed.
Many beginners use CdS for their first light-sensing projects because they are pretty easy to get setup: you create a resistive divider with the light sensor and a known resistor value, then measure the voltage with an ADC on a microcontroller – and backsolve to determine the mystery R value. With this you can measure basic light levels, and it works well because the resistance of the sensor changes pretty dramatically from a couple-hundred ohms to many-hundred-thousand ohms. Plus, you aren’t expecting to get precision lux readings, just “pretty dark” to “room lighting” to “very bright”!
That kind of rough estimation works great for beginners or simple light sensing, but will not cut it when you have to use a strain gauge at the supermarket to measure pounds of veggies: you want it to be very precise, at least within 1% or better! And if you’re using a temperature measurement for a scientific process, you may need to get within 1 degree C or better. You can usually improve the quality slightly by having a 1% or 0.1% precision resistor, adding an op-amp gain stage, upgrading your ADC from 8 or 10 bit to 16 or 24 bits – however, you will still need to adjust calibration from sensor-to-sensor as well as account for temperature and/or humidity.
That’s where the Renesas ZSSC3241 Sensor Signal Conditioning IC comes in! It’s designed specifically to make any resistive sensor easy to wire up and interface with SPI, I2C or 1-Wire. You can use Wheatstone half-bridge, full-bridge or divider configuration so it’s good for strain gauges or RTDs. There’s even analog output!
The ZSSC3241 provides measurement value readouts and programming capabilities via an I2C, SPI, or one-wire interface (OWI). Three different operation modes allow optimal development of digital, digital-analog, and analog-output smart sensor modules including wake-up on request, continuous-on/fast-response, and automatic/cyclic sensor measurement operations. Absolute and ratiometric voltage, current-loop, or interrupt analog outputs are supported by the ZSSC3241. The analog output options and digital interface options (for calibration and/or a digital application interface) can be combined.
Some great stuff that is included in this chip includes dual PGA stages with up to 300x and 1.8x gain, mV offset shift correction, 12 to 24 bit adjustable ADC resolution – lower resolutions will be faster, adjustable sensor bias current, adjustable temperature compensation, oversampling and averaging, error fault reporting, NVM storage for calibration details, interrupt output on value change, and configurable cyclic measurements with sleep mode – as well as many other configurations that you can check out in the datasheet. While there are many ADCs that one can use to read resistive bridge, we’ve never seen one with so many knobs for getting the exact right data out without needing a lot of extra massaging….and the pricing is great considering how much more you get than a normal off-the-shelf ADC chip.
If you want to get started fast, we recommend getting the ZSSC3241 Eval Board, particularly since it some with desktop GUI software that can be used to test out the zillions of configuration settings directly with your sensor of choice wired up, without having to go through a ton of re-compilation cycles.
Both the Renesas ZSSC3241 Sensor Signal Conditioning IC and Eval Board are in stock now for immediate shipment from DigiKey. Order today and you’ll get those chip in hand by tomorrow afternoon, so that when you are faced with your next resistive sensor project, you’ll skip the struggle and go straight to soft, silky, sensor success.
