1. Yuchen Chai, Pradeep Shenoy, Philip T. Krein
Signal Conditioning
Yuchen Chai, Pradeep Shenoy, Philip T. Krein

2. What Is Signal Conditioning
Many applications require environment or structural measurements, such as temperature and vibration, from sensors. These sensors, in turn, require signal conditioning before a data acquisition device can effectively and accurately measure the signal. Key signal conditioning technologies provide distinct enhancements to both the performance and accuracy of data acquisition systems.

3. Our Signal Conditioning Preliminary Design with Bread Board
Our Circuit Specifications
1.16 parallel signal inputs
2.Input Voltage magnitude is around 20V with some ripples
3. Output signal should meet Analog to Digital converter requirements which has 0 – 3.3V input range
4.Need low-pass filter

4. Our Signal Conditioning Preliminary Design with Bread Board
Our amplifier choice:
AD8226:  Wide Supply
Range, Rail-to-Rail Output
Instrumentation Amplifier
Flexible gain range from 1 to 1000
(really what we want in our circuit)
Our filter choice: First-Order
low pass filter with LM124/LM224/LM324/
LM2902:Low Power Quad
Operational Amplifiers

5. Our Signal Conditioning Preliminary Design with Bread Board
Bread board layout at the beginning with several bugs

6. Our Signal Conditioning Design
1st step – Amplification
Amplifiers increase voltage level to better match the analog-to-digital converter (ADC) range, thus increasing the measurement resolution and sensitivity.

7. Our Signal Conditioning Design
Test instrumentation amplifier functionality
We did not find AD8226 in ECE workshop, but we choose AD622 Low Cost Instrumentation Amplifier
(seems ok) and decided to test it functionality first

8. Our Signal Conditioning Design
Desired output (Red) from instrumentation amplifier and input (Green) with AD V power supply

9. Our Signal Conditioning Design
Our real output (Red) from instrumentation amplifier and input (Green) with AD V power supply :

10. Our Signal Conditioning Design
Output is distorted, but why?
After changing the DC offset, we found that this is because we set the cutoff voltage(also means the supply voltage to AD622) from 0 V – 10V (with only Pin7 connected). When the mean value of the input voltage is 1V-2V below 10V or 1V-2V above 0V, the output is the clip version of the input.
How to solve it? Really Easy!
Use Pin4 to give AD V to +10V power supply which can give our circuit more range. Some graphs are attached here.

11. Our Signal Conditioning Design
2nd step - Filtering
Test the functionality
We chose LM124 low power quad operational amplifier to act as a buffer and test its functionality, and we found it works correctly in the range of our input.

12. Our Signal Conditioning Design
“First-Order low pass filter” connect to the output from the instrumentation amplifier
we found the output signal from instrumentation amplifier is distorted which was not what we wanted to see
How to solve it? Really easy!
Instead of that complicated design, we choose to use “Passive low pass filter” which is much easier

13. Our Signal Conditioning Design
To make it more flexible with users’ requirements, we used a Trim potentiometer(small Blue box) to give a wide range of output from the low pass filter, and we got the desired result.

14. Our Signal Conditioning Design All Done!
Output from filter (RED) at 725.7mV
Output from instrumentation amplifier (BLACK)
Input (GREEN)
Smoother output voltage (RED) at 1.463V by changing trim potentiometer:

15. Summary
We found the AD662 and LM124 fit our specification and can be used in PCB design for the signal conditioning circuit. I am still searching the parallel trim potentiometer to change the input voltage range simultaneously. Next step is to design the PCB layout through software, order components from manufacturers, and build the PCB.

16. Continuous Study
1. PCB design on Eagle
2. Order the PCB board!

17. Selected Reference
“Operational Amplifiers and Signal Conditioning”, “What is Signal Conditioning? ”, National Instruments, “LM124 Low Power Quad Operational Amplifier”, National Instruments, “AD622 Low Cost Instrumentation Amplifier”, Analog devices, amplifiers/ad622/products/product.html “AD8226: Wide Supply Range, Rail-to-Rail Output Instrumentation Amplifier”, Analog devices, amplifiers/ad8226/products/product.html