As mentioned in my last post about cheap Chinese wireless temperature/humidity sensors, one of the three devices that I ordered was broken. It did show correct values on the local screen but no messages were seen over the radio link.

I decided to open it up to see if there’s anything obviously wrong inside. Here’s how the internals looked like:

The 2 working sensors both had the blue radio module shown on the left and the non-working sensor had the white module shown on the right. Since I had RTL-SDR I decided to see if the broken module sends out any signal at all. I found a very detailed blog post describing the steps for doing it.

Here’s what my signals looked like:

The topmost signal is from the broken radio module as measured ~30cm from the antenna. The next one is the signal from the replacement radio module from the same distance and the last 2 signals are from the two other sensors which were located much further from the antenna.

As we can see the broken signal is rather unstable and can’t hold stable high.
It looks even more interesting when zoomed in:

Here’s how the sensor looks with the replacement radio module:

The fixed sensor works rather well, the signal is clear from ~20m away through 2 concrete floors.