For some reason, the 32-bit versions of these operating systems don’t prevent the unsigned drivers from being installed, although they do complain.
There are a few workarounds that involve hacking Windows or disabling digital signature checking, but thanks to a tip by user wayneft on the Adafruit support forums, I was able to make the process much more straightforward. The USBTiny drivers are based on libusb-win32. Based on some notes I found on the libusb-win32 wiki, I discovered that the latest libusb drivers contain a proper digital signature…
I used the Windows device manager to upgrade the broken drivers on my Windows 7 64-bit machine. There is still a warning that “Windows can’t verify the publisher of this driver software” but there are no more errors about digital signatures and the new drivers appear to install and work correctly.
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As much as I would like this to work, it doesn’t work here. Still have to jump through hoops to use a non-signed driver.
It still doesn’t work here, windows update says I already have the latest driver and doesn’t offer an update. I downloaded the latest libusb driver but it didn’t work either.
This worked for me on Win7 Home Premium 64bit. The instructions on Jeff’s site isn’t all that clear – but when you download and unpack the zip file from his site, there’s a file called USBtiny.inf. Go to the Device Manager, click on the USBTinyISP device, right-click to update the driver, then manually browse to the inf file you just unpacked and select it. It will complain about the driver being unsigned, but if you choose to install it anyway it shouldn’t give you any more hassle.