Wireless battery voltage monitor for film/video sets. LoRa sensor nodes tap into camera batteries and broadcast readings to a handheld receiver with an e-ink display.
All boards: Heltec WiFi LoRa 32 V3 (ESP32-S3 + SX1262, 915 MHz)
Receiver also has: Waveshare 2.13" e-Paper HAT V4 (250×122, GDEY0213B74)
| Variant | Battery | Connector | Voltage range | Divider |
|---|---|---|---|---|
Onboard (OB) |
4S Li-Ion | D-Tap or AB 4-pin | up to 16.8V | R1=100kΩ, R2=22kΩ |
Block (BL) |
6S Li-Ion | AB 4-pin (inline) | up to 25.2V | R1=180kΩ, R2=27kΩ |
Voltage divider feeds GPIO7. A 100nF ceramic cap between GPIO7 and GND filters ADC noise. Power the MCU through a buck converter (Pololu D24V10F5 — 36V max input, 5V out) tapped off VBAT. Do not feed VBAT directly to the Heltec USB or VIN pin.
📐 Full wiring (both variants, with diagrams): WIRING.md 📌 Pin assignments, button controls & screen layouts: REFERENCE.md 📝 Firmware version history: CHANGELOG.md — current: v0.5.9
LoRa SX1262 (HSPI): CS=8, DIO1=14, RST=12, BUSY=13 | SCK=9, MISO=11, MOSI=10
ADC (sensor nodes): VBAT_PIN = GPIO7 (ADC1_CH6)
E-ink (receiver): CS=5, DC=4, RST=3, BUSY=2 | SCK=6, MOSI=1
| File | Flash to |
|---|---|
sensor_universal_heltec_v3/ |
Recommended node firmware — one board, 4S or 6S, type selectable |
sensor_onboard_heltec_v3/ |
Legacy onboard-only (4S) node |
sensor_block_heltec_v3/ |
Legacy block-only (6S) node |
receiver_wireless_paper_v1_2/ |
The handheld receiver (Heltec Wireless Paper) |
bench_ping_test/ |
Both V3s, to verify the radio link (set ROLE_PINGER per board) |
Universal node (sensor_universal_heltec_v3) replaces the two single-mode
sketches: one universal divider (200k/22k as built — 2×100k + 22k — 6S-safe with headroom) and a runtime battery
type (OB 4S / BL 6S) that sets the thresholds + broadcast type. Pick it on the
config page or long-press PRG to toggle. Identical firmware on every node —
no per-unit edits. It shows a big 7-segment voltage and the type in the corner.
USB test mode: the node sketches have
USB_TEST_MODE(default1) that reads the board's onboard supply (~4V) instead of the divider, so the TX → RX → e-ink chain can be validated over USB-C with nothing wired. Set to0for real monitoring.
Every node has two names:
- Permanent id — auto-derived from the chip's unique MAC at boot. Never
changes, guaranteed unique, and is the WiFi network name + the receiver's
tracking key. The universal sketch uses a type-independent
ND-7F3A(so toggling battery type updates the node in place); the legacy OB/BL sketches useOB-7F3A/BL-7F3A. - User name — the friendly label you assign over WiFi (
Cam A). Defaults to the permanent id until set. Shown on the OLED + handheld and broadcast.
Because the permanent id comes from the silicon, you flash the same firmware to every node — no per-unit edits. With the universal sketch even the battery type is a runtime setting, so one firmware truly covers every node.
T:<type>,I:<permId>,V:<voltage>,S:<status>[,B:<lipo>][,M:<name>]
Example: T:OB,I:OB-7F3A,V:14.73,S:0,B:3.95,M:Cam A
type—OBorBLpermId— permanent unique id (chip-derived), receiver's tracking keyvoltage— float, 2 decimal placesstatus— 0=OK, 1=WARN, 2=CRIT, 3=no source (camera battery removed/dead)lipo— node bridge-LiPo voltage (optional; the node stays alive on it to report S:3)name— optional friendly name (no commas)
Each node hosts a WiFi access point you can join to rename it — no reflashing:
- Power the node and join WiFi
Brickdup-OB-7F3A(passwordbrickdup) — the suffix is unique per board, printed on the OLED at boot - Open http://192.168.4.1
- Type a name, tap Save
The name persists in flash (survives reboot/reflash) and rides along in every packet, so the handheld shows it automatically.
Turning WiFi off (saves ~80mA): no extra hardware needed —
- Tap the node's onboard PRG button any time to toggle WiFi on/off, or
- Hit Turn off WiFi on the config page when you're done naming.
Press PRG again to bring it back. The on/off choice is remembered across
reboots — a node switched off stays off after a power cycle. WIFI_ON_AT_BOOT
is only the first-ever-boot default.
| Unit | Single tap | Long press | Triple tap |
|---|---|---|---|
| Node (PRG) | toggle WiFi | — | power off |
| Receiver (USER) | page nodes | toggle dashboard | power off |
"Power off" is deep sleep (~10–20µA); the screen shows POWERED DOWN (white on black), then press the button again to wake (the unit reboots). The receiver e-ink keeps the POWERED DOWN screen visible while asleep.
Thresholds (defaults, editable per type in the node portal) — Onboard: WARN=13.5V, CRIT=12.8V | Block: WARN=21.0V, CRIT=20.0V
Frequency: 915.0 MHz | Bandwidth: 125 kHz | SF: 9 | CR: 4/5
Sync word: 0xAB | TX power: 17 dBm | Preamble: 8
All nodes must use identical settings. SF9 gives 50–100m range with obstacles. Up to 12 nodes, 10s interval — no collision concern.
Arduino IDE 2.x with the Heltec ESP32 board package (Board Manager URL):
https://resource.heltec.cn/download/package_heltec_esp32_index.json
Board selection differs per sketch (the e-ink library requires the exact board, or it errors with "Wrong build env"):
| Sketch | Tools → Board |
|---|---|
receiver_wireless_paper_v1_2 |
Wireless Paper (search "paper") |
sensor_universal_heltec_v3 |
Heltec WiFi LoRa 32(V3) |
sensor_onboard_heltec_v3 |
Heltec WiFi LoRa 32(V3) |
sensor_block_heltec_v3 |
Heltec WiFi LoRa 32(V3) |
Common settings: USB CDC On Boot → Enabled | Upload Speed → 921600
OTA updates (no USB after the first flash): every unit's web portal has a
/update page. Build a .bin via Sketch → Export Compiled Binary, join the
unit's WiFi, open its /update page (linked from the config page / dashboard),
and upload the matching .bin — it flashes the spare partition, verifies, and
reboots. Upload the OB .bin to onboard nodes, BL to block nodes, receiver to
the receiver (the page shows which it expects).
No partition setting needed: the Heltec WiFi LoRa 32 V3 and Wireless Paper both default to the
default_8MBscheme, which already has two ~3.3MB app slots (OTA-capable). There's no "Partition Scheme" menu for these boards because the partition is fixed — and it's the right one.
GitHub Actions compiles all three sketches on every push and on version
tags — no local toolchain needed to get a .bin:
- Every push: download
brickdup-firmwarefrom the latest Actions run (artifacts:brickdup_onboard.bin,brickdup_block.bin,brickdup_receiver.bin). - Tagged releases: push a
vX.Y.Ztag → the.bins are attached to a GitHub Release.
Grab the matching .bin and push it to a unit via its /update page. To cut a
release: bump FW_VERSION in all three sketches, update CHANGELOG.md, commit,
then git tag v0.5.1 && git push --tags.
Libraries (Library Manager):
RadioLibby Jan Gromeš — all three sketchesHeltec ESP32 Dev-Boardsby Heltec — node OLED (HT_SSD1306Wire.h)heltec-eink-modulesby todd-herbert — receiver e-ink (pulls in Adafruit GFX)
| Part | Source | ~Cost |
|---|---|---|
| Heltec WiFi LoRa 32 V3 (915 MHz) — nodes | Amazon | $22 ea |
| Heltec Wireless Paper (915 MHz) — receiver | Amazon | $22 |
| Pololu D24V10F5 buck converter (per node) | Pololu | — |
| Node LiPo — MakerHawk 1100mAh 1S (JST 1.25) | Amazon B0F9YSFV4T |
4-pack |
| Receiver LiPo — MakerFocus 3000mAh 1S (JST 1.25) | Amazon B08T6GT7DV |
4-pack |
| D-Tap male connectors | B&H (CT-DTAP-M) | — |
| AB 4-pin connectors | Pinknoise Systems / Trew Audio | — |
| 1% metal film resistors — universal: 200k, 27k (legacy: 100k/22k, 180k/27k) | — | — |
| 100nF ceramic caps (104) | — | — |
- Bench ping test (verify radio link before analog wiring)
- Receiver paging (USER button cycles pages when >5 nodes)
- Fuel gauge: SoC % + rough time-to-empty per node (voltage-based)
- Calibration (enter true voltage on the web page; gain factor saved to NVS)
- RSSI signal bars per node on the receiver
- Receiver web dashboard (live node table on your phone; long-press USER)
- OTA firmware update via the web portal on all units (/update page)
- Captive portal — config page auto-pops on WiFi connect
- Universal node — one sketch, runtime 4S/6S battery type (web or long-press)
- Prebuilt firmware via CI (GitHub Actions builds .bin on every push)
- Channel/group selection — separate networks via distinct frequency + sync word per channel, set on the node web page and on the receiver, NVS-stored. Lets multiple brickdup systems coexist (e.g. 1st/2nd unit)
- WiFi client (STA) mode — units optionally join a local network (DHCP or
static IP) instead of hosting their own AP, each reachable at a unique
mDNS host like
brickdup-7f3a.local(chip-serial based). Credentials set via the AP config page, stored in NVS. Reach/OTA any unit from one device on the production WiFi - Trusted WiFi networks — a saved list of known SSIDs the unit auto-joins (STA) when one is in range and WiFi is on, falling back to its own AP otherwise. Set via the config page, stored in NVS
- BLE / companion phone app — receiver exposes node data over Bluetooth LE
(GATT, mirroring the
/dataJSON) for a phone app: live view + push notifications for CRIT/DEAD batteries (alerts even with the handheld in a bag), no WiFi join needed. NimBLE stack; LoRa is a separate radio, BLE time-shares 2.4GHz with WiFi - iOS app — native companion that keeps a persistent live readout of all nodes and fires push/local notifications on CRIT/DEAD/LOST (even when backgrounded or the phone is locked). Connects via BLE (Core Bluetooth background mode) to the receiver; the front-end for the BLE item above
- Bridge LiPo on nodes — small backup cell (buck keeps it charged) so a node stays alive to report a camera battery removed/dead for sure (vs just going silent), survives swaps, and reports its own LiPo level. Replaces the receiver's inferred DEAD with an explicit reported one
- VCLX block-battery mode (NiMH) — the blocks in use are Anton/Bauer VCLX NM2 (600Wh NiMH), tapped at a 14.4V 4-pin XLR. Per the manual spec table, only 28V/48V (+5V USB) are regulated; the 4-pin XLRs are variable 12–17V (pack-following) — so the node does see a real discharge curve. But the chemistry breaks the Li-ion fuel gauge: NiMH holds a flat ~14.4V (1.2V/cell × 12) for most of the discharge, knees at ~13.2V, and the battery hard-cuts its output at 12.0V (output vanishes → bridge LiPo keeps the node alive to report DEAD). Repurpose BL mode → NiMH profile: thresholds ≈ WARN 13.2 / CRIT 12.4, and suppress SoC%/time-to-empty (or fit a rough NiMH curve) — the Li-ion curve reads nonsense on the flat middle. Verify thresholds on a real pack: meter the XLR full (~16.8V) vs drained. Heads-up for the divider bench test: cap input at ~17V for this mode, not 25.2V
- CRIT buzzer alert on receiver
- NVS persistence — receiver remembers nodes across reboots (clear on dashboard)
- Deep sleep on sensor nodes (~10µA between transmissions)
- PCB design (sensor node, two variants or DNP options)