Hello Sir,
I am a full time working freelancer and I am available on freelancer most of times and I can provide you the required prototype as you want it.
I have very good feedbacks from my previous employers and I have been doing prototyping for many years. Regarding your project,I have experience in SIM900 and several temperature/voltage sensors. I can complete this perfectly.
Please contact me if you are interested. I have attractive milestone planes that assure the satisfaction of both parties. Thank you
Anthony