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Fix Heltec V4 Vext polarity (OLED never powered)

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The V4's Vext rail switch is a PMOS: GPIO36 LOW turns the rail ON.
The DTS drove it ACTIVE_HIGH, leaving the OLED (and its I2C pull-ups)
unpowered — the rail floats at ~1.6V and SSD1306 init always fails
with -ETIMEDOUT.

Verified on hardware with a multimeter: GPIO36 high = 1.6V on Vext,
GPIO36 low = 3.3V, display works.

This matches what the working Arduino MeshCore firmware actually does
with the pin, despite its PIN_VEXT_EN_ACTIVE=HIGH define:
RefCountedDigitalPin::begin() initialises the pin to its *inactive*
level (LOW), and the V4 OLED build constructs the display with a NULL
periph_power (variants/heltec_v4/target.cpp) so nothing ever claims
it HIGH. GPIO36 is therefore driven LOW continuously under Arduino —
the exact state this fix reproduces via an ACTIVE_LOW boot-on
regulator.
This commit is contained in:
Étienne Fesser
2026-07-06 19:26:17 +02:00
parent eff498b64c
commit 2a26e830e2
1 changed files with 9 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files
zephcore/boards/esp32/heltec_wifi_lora32_v4/heltec_wifi_lora32_v4_procpu.dts
+9 -6
View File
@@ -8,7 +8,7 @@
* OLED: SSD1306 128x64 on I2C0
* Button: GPIO0
* LED: GPIO35 (PWM via LEDC0)
* Vext: GPIO36 active-HIGH (powers OLED and sensors)
* Vext: GPIO36 active-LOW PMOS rail switch (powers OLED and sensors)
* BatADC: GPIO1 (ADC1 ch0), enable GPIO37 active-LOW
*
* V4.2 (this file) — GC1109 PA, TX_EN on GPIO46.
@@ -20,7 +20,7 @@
* GPIO7 = VFEM_Ctrl LDO power (active-HIGH, always-on)
* GPIO2 = GC1109 CSD (chip enable, active-HIGH)
* GPIO46 = GC1109 CPS (TX mode select, active-HIGH)
* - Vext control is active-HIGH (was active-LOW on V3)
* - Vext rail switch is active-LOW (PMOS; GPIO36 low = rail on)
* - DIO2 used as RF switch alongside external FEM TX control
*
* LoRa SPI2: SCLK=9, MOSI=10, MISO=11, NSS=8
@@ -85,13 +85,16 @@
full-ohms = <(100000 + 390000)>;
};
/* Vext — powers OLED and external peripherals (active-HIGH on GPIO36).
* regulator-fixed + SSD1306 vin-supply: powers rail at boot without relying on
* power-domains (CONFIG_PM_DEVICE is disabled in prj.conf). */
/* Vext rail switch — PMOS, ACTIVE LOW (GPIO36 low = rail ON).
* Powers the OLED (incl. its I2C pull-ups) and the expansion header.
* Verified on hardware: GPIO36 driven high leaves the rail floating
* (~1.6 V) and the OLED unpowered; driven low gives a clean 3.3 V.
* regulator-boot-on + always-on: the rail comes up at regulator init,
* well before the SSD1306 driver init. */
vext_enable: vext-enable {
compatible = "regulator-fixed";
regulator-name = "vext";
enable-gpios = <&gpio1 4 GPIO_ACTIVE_HIGH>; /* GPIO36 = gpio1 pin 4 */
enable-gpios = <&gpio1 4 GPIO_ACTIVE_LOW>; /* GPIO36 = gpio1 pin 4 */
regulator-boot-on;
regulator-always-on;
};