Testing Message Delivery

A project log for LoFi

LoFi is a very low cost ($5), small, auto-transmitting module. Preassembled and preprogrammed. Simply attach to your appliances or projects!

david-cookDavid Cook 06/26/2014 at 03:040 Comments

Summary: Delivery Tester indicates LoFi works well through walls and across the house

I built a simple test harness in C# .NET that visually displays the success or failure of receiving messages using LoFi on the 433 MHz band. The transmitter is running at 3 volts and is located approximately 75 feet away and down a floor. Each message is 21 bytes in length: 6 byte header, 8 byte message (five analog pins, a digital pin, voltage reference, and internal temperature), and 7 intermingled bytes of Hamming error correction.

As you can see, most of the messages were delivered successfully (green squares). Those that aren't (blank spots) would be covered by retries or could be ignored if they are highly redundant status updates -- such as for water level or temperature monitoring. Hamming code fixed 11 bit errors. Six bit errors were not corrected and caused some of the bad messages.

The bad messages generally occur in bursts, usually due to RF interference such as electrical noise or another 433 MHz device. However, as you'll see in the video, the errors towards the end are caused by operator rough handling. So, the actual delivery percentage is much higher.

Live action video: