On Sat, Mar 28, 2020 at 02:09 PM, K9HZ wrote:
My virus protection lit up when I clicked on that link!!!?
Here is the quick version of that link. My Mac did not see a virus, hopefully it was not in error.?
Basically it was a LM358 op-amp circuit for an inexpensive strain gauge pressure sensor. Amazon said no more were available in your region due to high demand when I clicked on the amazon link in the article.
The offset and temperature specs for that op-amp may need to be evaluated to see if they are adequate. Also, it is common to use one of the analog inputs to measure the voltage considered to be the "center" voltage, where a non split power source for the op-amp is used and/or a "zero" reading voltage so the processor can compensate for the offset of any op-amps and the offset of the A/D converter itself. The development board that I pulled the chopper stabilize op-amp from would shut off all the auto-ranging jets and use that as a reference. Because the chopper stabilized op-amp is very low drift and offset, that may not be necessary.?
Since it looks like we are going with the I2C?barometer sensor for the safety sensor and an analog sensor that produces a large enough voltage to directly feed the A/D of the Nano, for the flow sensor, it looks like any need for op-amps to amplify sensor signals is not needed. If op-amps were needed, the best place may be on a board with the sensor, so the gain and other design parameters could be tailored to the sensor. This could allow for retrofitting the currently selected sensors if supplies get short. A spare analog input would be nice if the I2C sensors ran out of stock and a strain gauge sensor had to be used.?
Tom, wb6b
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