Updating Thingspeak channel field1 with array of data | ThingSpeak API | Forum

The maximum for each field is 255 characters. It is not the recommended use to put more than one data point in each field, but it is possible to put multiple values in. You will need to parse the values when you retrieve the data.
You can also cut your data up into multiple segments and write it across the 8 fields every 15 seconds.

ThingSpeak will treat your entry as a string so you can use any delimiter you like to add multiple values. If they are fixed width, you wont need any delimiter at all. When you update the field, simply append all the values to the end of the GET. For example:
https://api.thingspeak.com/update?api_key=xxxxxxxxxxxxxxxx&field1=0123456abcdefg_or_1,2,3,4,5,a,b,c,d
This command will write
"0123456abcdefg_or_1,2,3,4,5,a,b,c,d"
to field1.
Then you can parse it to separate the values.
If you add &field2= you can addinformation to field 2 in the same write.
https://api.thingspeak.com/update?api_key=xxxxxxxxxxxxxxxx&field1=0123456abcdefg_or_1,2,3,4,5,a,b,c,d&field2=4.345