We considered battery pack options; lithium ion was considered for its weight and energy density but this was discounted due to risks around battery damage and high temperature charging. So, we chose a battery solution which resolved both the safety concerns and the risk of damage to the product.
Next we considered switches and force sensors looking at a wide variety of solutions. Initially we found the desired force sensor contributed around 80% of the cost of the product. So, we set about investigating ways of achieving the same thing without the cost. As we developed the design it became clear that the force sensor didn’t require a high degree of accuracy. It just needed to be enough to recognise a touch.
We began prototyping the sensor using various materials and PCB patterns. The solution we developed was 1/10th of the cost of the original force sensors with a cost of $0.2 vs force sensor cost of $22 – a significant saving indeed.
With the prototype sensor produced the rest of the product was architected into several individual PCBs connected by off shelf flat flex PCBs. We evaluated the options of flexi- and rigid-flex pcbs here. At the initial launch volumes these add cost without bringing much benefit. This can be revisited as sales volumes increase.
The PCB designs were completed, firmware written, prototype bring up completed and tested and samples shipped for testing and feedback.