I found that I had to manually install the Windows 7 device drivers since they did not automatically install and Windows could not find drivers by itself. The instructions on the FTDI website are not entirely clear, so here are some additional notes.
* Follow Windows 7 Installation Guide from FTDI website
* Download both the D2XX driver and VCP driver (links are given in the installation guide), choosing the drivers appropriate to your computer’s CPU (e.g. a new computer is likely 64 bit, whereas if you are using an older laptop you might need the 32 bit x86 driver)
* The D2XX and VCP drivers confusingly have the same name, so save them into separate empty folders called, say, D2XX and VCP so you can keep track of which is which
* They need to be manually unzipped after downloading
* The first driver that is being installed in the install guide instructions is the D2XX driver
* From Device Manager, right click the device name. The Mayfly will come up under “Other devices” and be called something like “Unknown device” or “FT232R USB UART”. If it is not clear which device is the Mayfly, unplug it and watch to see which device is added when you plug it back in.
* Select *Update driver software*
* Select *Browse my computer …* – browse to and select the D2XX driver folder that you downloaded and is now unzipped (e.g. “CDM v2.12.28 WHQL Certified”)
* After installing there should be a “success” message from the installer but there may also be a separate Windows tray notification saying “failed”. This appears to be normal (the failed message appears to be indicating that a COM driver is not yet installed).
* The second installation is the VCP driver, which is the COM driver.
* Basically, repeat the same steps as the first installation but this time choose the VCP driver
* After installation the mayfly should show up in Device Manager as “USB Serial Port (COMX)”, where X is the COM number assigned to the device.