some ideas about accuracy...
i have just gotten my sr04 and played a lithe with it. i intend to use it to measure oil level in a tank. so accuracy is quite important.
after reading on the web there are two main points that seem to influence the accuracy of the sensor and both are not accounted for in the newping library:
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one is temperature. it would be nice to be able to set the temperature that newping uses for the conversion to cm/inces. depending on the temperaure the error can easily be in the range of 10% if temperature is not accounted for.
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the other one is the which echo is received and evaluated. if i do repeated measurements i notice that the results will be relatively near around two or tree that are themselves further apart. this looks like it is consistent with some articles that say this error comes from reading the second or third echo and not the first and should be especialy noticeable in the short range.
so to be able to make more accurate measurements i started reading 10 or 50 pings, iterating over all of them and throwing away all that are equal to the largest and all that are equal to the smallest and then averaging the rest. if there are non available after throwing the smallest and largest away i take the smallest. the conversion to cm is then done in float.
this seems to give very accurate and reproduceable results. doing this repeatedly in a range of 1cm to 1m gives identical results up to at least 1mm.
maybe a 'slow scan' option could add this to the newping library for applications where fast response times are not needed.