Here is a great checklist for wearable devices. When we do a design we check all of these things and more. Often we need to use our engineering judgment on the tradeoff between size, cost, testability, and manufacturability of the board.
- What size battery?
- What is the appropriate battery lifetime?
- How often do various parts of it need to be on?
- What is the maximum current draw (also determines battery size)?
- How will the battery be charged: wirelessly, plugged in, or replaceable batteries?
- What is the appropriate type of wireless transmission?
- Is a gateway needed or will it connect directly to the Internet?
- What is the impact on the battery, size and lifetime?
- What type and size of antenna is needed?
- How often does it need to be on?
- What is the appropriate tradeoff between cost and accuracy?
- What accuracy and sensitivity is needed? Is calibration needed?
- How will the sensors be tested and calibrated?
- If there are biological sensors, how will the signals be picked up from the body, contact or non-contact, invasive or non-invasive?
- What is the bend radius?
- Where does the data analysis take place, on the device or elsewhere?
- How smart does the device have to be (smarter generally means more power and larger)?
- What is the protocol for communication, standard or proprietary?
- How will software updates be done, over the air, by plugging in, or not at all?
- Will there be wired communication? During charging?
- How small is the space for electronics?
- How will everything fit?
- Where will the antenna be located (away from metal and not too close to the body)?
- Does it need to be sealed from dust and moisture? To what water depth is it sealed?