Bolt posted a blog on Who invests in hardware startups?. Bolt is a small VC that invests in startups, and their blog describes three VC categories that includes:

• Small hardware only VCs
• Hardware friendly micro VCs
• Hardware friendly traditional VCs

The two small VC firms don't tend to lead rounds so if you pull in a traditional VC, then the smaller VC might then participate. Anyway, the trend for hardware startup is looking good with increasing number of rounds funded and increasing funding year over year.