Recording of sensor results but only retain the last 3 sets of data

Question

I'm doing a radiation-seeking robot, which will find the source of the radiation autonomously. But in this case, my robot will spin 180 degrees to detect the nearest source of radiation and 1 set of data recorded is considered for every 180 degree turn. However I think it is not possible to store all of the data in the Arduino due to a storage problem.

Therefore is there any function in Arduino that can only record the last 3 sets of data from the sensor? For example, after it has recorded 3 sets of data, the fourth set data could be recorded by overwriting the first set of data. I would be really grateful if anyone could help me with this.

PS if possible I don't want to install an SD card in my Arduino.

Answer 1

It depends how big the data is... if one data set is 100 bytes, you can spend 300 bytes of internal SRAM memory.

What you also can do if the memory usage is too big, is to add external SRAM, like the 32K256 which has 32 kb (kilobyte) SRAM or the 23LC1024 which has 128 kb SRAM.

To loop through the data sets you can easily use a so called 'ring buffer'.

You allocate 3 sets of data (like 3 arrays of a byte array), and an index. the index you increase after every use like:

index = (index + 1) % 3 

External SRAM normally uses SPI to communicate with, and you can read/write it by a single byte, multiple bytes or page (typically 128 to 512 bytes). You cannot directly store variables in it, but you have to manually keep track where you store what ... for 3 data sets this will be relatively easy. You can even calculate (beforehand) the number of data sets that can be stored and cycle through them as needed.