barbell probe (wip)

x 0.35 · purpose 0.70 · t 2 s · scope 0.40

from 2026-10

ESP32-C3 · ICM-42688-P · BLE · C++

A lift is a repeated movement, but most workout records contain only weight and repetition count. The barbell probe is an ESP32-C3 motion tracker that attaches to a barbell or moving weight stack and turns each repetition into a path, a tempo and a set of measurable phases.

a rep as a trajectory

Barbell bench press, 8 reps. The bar path at 1:1 in the device's frame: the bar descends about 37 cm from its start, reverses and returns, drifting -4 to 26 mm sideways. Beside it, each rep's vertical travel against time, with earlier reps kept faint and each reversal marked.

data

rep	rom (cm)	lower (s)	lift (s)	cycle (s)	counted at (s)	reversal z (mm)	reversal x (mm)
1	37.2	1.08	0.81	2.49	3.21	-375.0	19.2
2	38.0	1.10	0.84	2.52	5.76	-383.1	19.4
3	37.5	1.13	0.87	2.57	8.33	-377.2	17.3
4	36.5	1.12	0.89	2.59	10.93	-367.4	17.5
5	37.1	1.15	0.91	2.63	13.57	-373.5	15.3
6	35.7	1.18	0.95	2.73	16.29	-359.5	18.6
7	34.8	1.20	1.00	2.78	19.09	-352.0	18.5
8	35.5	1.23	1.07	2.92	21.98	-358.4	20.1

a repetition becomes a line with a beginning, reversal and return.

The main object is the movement itself: a thin trace written across an otherwise empty frame. Position advances with time, pauses at the end of the range and returns. Previously completed reps remain as faint references, so the movement reads without a photo of the gym or the device.

an entire set

Cable-row weight stack, 10 reps over 30.7 s. The stack rises above its start on every rep, so its trace runs upward. Range of motion 43.1 cm on average (2.45% variation); each rep's range and lowering and lifting time sit under it.

data

rep	start (s)	rom (cm)	lower (s)	lift (s)	cycle (s)	counted at (s)
1	1.00	43.4	1.24	0.83	2.65	3.23
2	3.65	44.2	1.25	0.84	2.69	5.90
3	6.34	43.8	1.27	0.87	2.75	8.66
4	9.09	44.7	1.29	0.85	2.74	11.41
5	11.83	43.1	1.31	0.90	2.84	14.23
6	14.67	43.9	1.33	0.92	2.88	17.12
7	17.55	42.6	1.34	0.96	2.93	20.05
8	20.48	42.3	1.36	1.00	3.01	23.05
9	23.49	41.8	1.37	1.03	3.04	26.11
10	26.53	41.2	1.41	1.08	3.17	29.25

range, pace and movement phase accumulate across the set.

Alongside the primary trace sit small fields for repetition number, range of motion, direction, and lifting and lowering time. The examples are a bench-press set and a moving cable-row stack; the two traces run in opposite signed directions relative to their starting position.

device to phone

The ESP32-C3 reads its ICM-42688-P at 100 Hz, marks each motion phase on the device and sends the phone a BLE notification every 100 ms: 234 frames and 8 counted reps in the bench-press set, from connect and tare to save. The load is entered in the phone; the sensor measures motion only.

data

set	t (s)	from	to	event
BP-042	0.00	phone	device	ble connect
BP-042	0.12	device	phone	ready
BP-042	0.20	phone	device	set config
BP-042	0.26	phone	device	tare
BP-042	1.00	device	phone	tare ok
BP-042	1.15	phone	device	start set
BP-042	1.20	device	phone	set started
BP-042	3.21	device	phone	rep 1 · 37.2 cm
BP-042	5.76	device	phone	rep 2 · 38.0 cm
BP-042	8.33	device	phone	rep 3 · 37.5 cm
BP-042	10.93	device	phone	rep 4 · 36.5 cm
BP-042	13.57	device	phone	rep 5 · 37.1 cm
BP-042	16.29	device	phone	rep 6 · 35.7 cm
BP-042	19.09	device	phone	rep 7 · 34.8 cm
BP-042	21.98	device	phone	rep 8 · 35.5 cm
BP-042	23.33	device	phone	set ended
BP-042	23.36	phone	device	save set
BP-042	23.43	phone		set saved
WS-016	0.00	phone	device	ble connect
WS-016	0.12	device	phone	ready
WS-016	0.20	phone	device	set config
WS-016	0.26	phone	device	tare
WS-016	0.80	device	phone	tare ok
WS-016	0.95	phone	device	start set
WS-016	1.00	device	phone	set started
WS-016	3.23	device	phone	rep 1 · 43.4 cm
WS-016	5.90	device	phone	rep 2 · 44.2 cm
WS-016	8.66	device	phone	rep 3 · 43.8 cm
WS-016	11.41	device	phone	rep 4 · 44.7 cm
WS-016	14.23	device	phone	rep 5 · 43.1 cm
WS-016	17.12	device	phone	rep 6 · 43.9 cm
WS-016	20.05	device	phone	rep 7 · 42.6 cm
WS-016	23.05	device	phone	rep 8 · 42.3 cm
WS-016	26.11	device	phone	rep 9 · 41.8 cm
WS-016	29.25	device	phone	rep 10 · 41.2 cm
WS-016	30.70	device	phone	set ended
WS-016	30.73	phone	device	save set
WS-016	30.80	phone		set saved

the sensor measures motion; the phone keeps the set.

An IMU provides accelerometer and gyroscope readings, while the phone receives motion and rep events over BLE. The device interprets relative movement; the user enters the load separately, because the sensor never measures the weight being lifted.