Requirements for the choice of force sensor are:
- size
- availability
- electrical connectivity
- need for signal amplifier

Due to the size and shipping restraints, the round FX1901 strain-gage sensor is picked. The plastic housing can be removed to reduce the size of the unit. Force is applied on the center bump. With a diameter of 19,2mm, it is suitable to be mounted into the foot of a crutch.


 The sensor features 4 strain gages in a configuration that is readable for the HX711 signal amplifier.



Microcontroller:

The main requirement characteristics for the choice of microcontroller are:
- size
- wireless connectivity
- low-power sleep modes
- power consumption when in use
- cost

Since the first demonstrator unit of the intelligent crutch is to be built purely as a function demonstrator, the size and cost requirements are secondary. Wireless connectivity is a must, also low power consumption in standby and use should be demonstrated.


The TinyPICO is a ESP32 board which is very small (18mm x 32mm). Compared to most regular ESP32 development boards, the number of breakout-pins has been reduced. This will not affect the project, since only a small number of sensors need to be connected.
The TinyPICO offers a very low power consumption of 20uA when in deep sleep.
This suits the use case very well, since it is possible to leave the device turned on for long periods of time with no use.
The board is prepared to be powered directly from a single-cell lithium battery. This suits the use-case of a crutch very well, as the device must be very mobile.


The TinyPICO Nano is a different variant of the same ESP32 board, which is SMD. The size is therefore reduced to 13mm x 27mm.


It is well suited for the integrated PCB variant of the intelligent crutch. Manual soldering is possible.
The very small width make it theoretically possible to fit the Microcontroller board into the tube of the crutch.