http://marcbarros.com/how-to-fund-a-hardware-startup

You should consider the following to calculate the right amount of capital.

• Product: After shipping an MVP you need to follow up quickly with version 2 to fix all the bugs and poor customer interactions. You’ll want to calculate what it costs in people and production to make your existing product F*#$ing great.
• Customer Love: A key part to reaching market fit is having customers that can’t stop using your product. Understand what it takes to fully engage your existing customers, including offering amazing customer support.
• Cost to Acquire Customers: One of the hardest parts of making a successful hardware business is profitably reaching new customers. You need enough capital to try a variety of tactics with financial systems to measure which are and aren’t working.
• Limited Distribution: Reaching market fit has nothing to do with building successful retail channels. To be great in-store it requires experienced people and a heavy investment in training. On top of that, it will strain your cash with delayed payment terms and lower margins. Save retail for after you reach market fit.
• Working Capital: Your most important cash consideration is your working capital (the time between collecting cash and paying your supplier). Managing your cash flow is critically important as you try to grow from an interesting product to a profitable business.

When you are ready to look for capital you can consider:

• Cash Flows: You don’t have to raise money. If your business is driving great cash flows you can use that cash to fund the business.
• Debt: Banks will give you about 80 cents for every dollar in receivables and 50 cents for every dollar in inventory. The key is that you have to be profitable. If not, it will be hard to get bank debt.
• Factoring Receivables: If you have strong receivables, but are not yet profitable you can factor your AR. It’s insanely expensive, up to 20% interest, but it can work to move cash flow if you get stuck. This is a last resort option.
• Your Supplier: Continuing to work with your supplier to improve your payment terms is critical to minimizing your cash requirements. You can offer to pay more per unit in exchange for better terms.
• Angels: If you are raising a smaller amount, say $1.5M, then you can approach angels, but asking for more will be an uphill climb.
• Venture Capital: Find a partner with experience investing in hardware and a belief that founders can become great CEO’s. You want the right partner so don’t make this choice lightly. Once you raise institutional capital, the requirements change dramatically.