Hi Js, and thanks for your interest in my project. While it's possible (in theory) to make it work for an Uno board, it's not advisable. The reason for this is that Uno only have one hardware serial line, whereas this project requires two. In theory, you could use the "USB" line (and disconnect the GPS while downloading), but then you will loose all debugging, testing and monitoring capabilities. I don't think I've ever made a project work on first try without any adjustments and testing, so it would make things a lot harder. And you would then need to adjust the code without any means to monitor and test it properly. So I'd say you are better off getting the right board to make this work :)

Having said that, you don't need the Leonardo board though. The code could be adjusted to work with other boards as long as there are two hardware serial lines, like the Mega or others.

Its a little late update on the issue, but I found that the SIM900 chip needed a firmware upgrade to enable the "CONTENT" option for the AT+HTTPPARA command. Without this command the HTTP header will not include "content-type: application/json" which it needs. If it does not, it returns a 400 "bad request". This worked previously, but in May thinger.io changed the API somehow and it stopped working. So I had to update the firmware to make it work again, I have updated this guide with this information too.

However, you have a different chip, so this might not be the issue, but can't hurt to check. An easy way to test this is by using https://requestcatcher.com and not the thinger URL in the code. The HTTP POST request will then be shown in plain text at this site, and what you are looking for is the "content-type" section. If its not there, you have a problem.. maybe look into the firmware issue as mentioned.

Hi Samantha! Glad you found it useful! I try my best :)

I'm not familiar with the sim800 models although I've seen that it is what I should have used as its replacing the older sim900. Are you also posting to thinger.io or just a HTTP post request in general?

The 400 return code just means "bad HTTP request", so the request is rejected. The message basically says that "something is wrong with your request". This can come down to anything really, what you are essentially doing is building the HTTP POST request with all attention commands (AT commands) before sending it with"HTTPACTION=1". So any of the previous AT commands can be wrong in one way or another. The things I struggled with that you can check:

• Wrong/bad URL, e.g. using https and not http, wrong address, syntax error.
• Missing quoation mark around text, small things like this.
• I struggled for a long time with the byte count in "AT+HTTPDATA=<byte count>,<input delay>". This byte count has to be exact for your string which you send, otherwise it won't work. Took me quite som time to figure that one out.
• If using thinger.io, make sure the authorisation key is correct.
• the data fields in the "content" section needs to be in exact order and syntax otherwise you will get problems, e.g. { field1 : field1_value , field2 : field2_value } etc.
• Thinger.io bucket must also be set to "From Write Call" to enable HTTP write requests

If any one of these things are wrong, you might get that return code (or similar).

If none of that works, I think you are better off posting your code and serial output in the forum section, that way it's easier to see the code and what might be wrong.. it always helps to have some context