It just goes to show that perseverance sometimes pays off. It turns out that the reason I couldn’t get the Olimex esp8266 to work properly was that my USB/serial converter was faulty. The replacement one arrived today, and now I can program the wifi module using the arduino IDE with no problem. Five seconds after programming it, it had connected to my home network and was sending temperature readings via MQTT to my raspberry pi server. There are plenty of IO pins exposed on the Olimex module, so I can do lots more with it than with the wi07c module I was using before. Watch this space.