Feather m0 adalogger

We developed a ring-shaped wearable device capable of measuring hand movements and estimating the flexion angle of each finger [28 ]. As shown in Fig. 1A, the device consists of a light-emitting diode (LED) (Osram, SFH4550) and a phototransistor (Honeywell, SD5410) [30 ]. The device was worn on the proximal phalanx of the index finger (Fig. 1B). The microcomputer (Adafruit, Feather M0 Adalogger) and a LiPo battery (3.7 V, 400 mAh) was installed in a white wrist box.Fig. 1

The developed ring device. A The ring device consists of an LED and a phototransistor. B The ring device was worn on the proximal phalanx of the index finger. A microcomputer, an accelerometer, and a battery were installed in a white wrist box

The ring-shaped device measures the distance between the fingertip and the device (d(n)) at 100 Hz. Based on a pre-measured length between the fingertip and PIP joint (L), the flexion angle of the PIP joint $\theta (n)$ can be estimated as $\theta (n)=arccos(d(n)/L)$ , where n is the time-step sampled every 10 ms [28 ]. The cumulative angular change is recorded as finger usage, and the cumulative norm of the wrist accelerometer is simultaneously recorded as upper-limb usage [31 (link), 32 (link)]. Simultaneous measurement with wrist and finger sensors enables separate finger movements from whole upper limb movements.

The biologger has an 8-pin programming and communication port where a “data dump” can occur using a standard two-wire serial protocol. A dedicated module was built for this function using an Arduino microcontroller with an onboard micro-SD card (Figure 3B; Feather M0 Adalogger, Adafruit). In brief, after biologgers were explanted, extracted from their case, and cleaned, a custom 3D-printed clamp with an 8-pin pogo connector was used to break out the biologger programming pins. The biologger was then inserted into the data dump module and data was transferred from the biologger memory module to the micro-SD card. Although we also created a wireless data retrieval utility, having a dedicated system to offload data was simpler. Once the data is retrieved, the biologger is ready to be reused, sparring only the soldered electrode connector which is met with epoxy during encasing.