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Fetching component info.

Looking for "strapping pins GPIO12 GPIO5 GPIO15 internal pull-up pull-down and boot configuration recommendations" in esp32-wroom-32_datasheet_en.pdf

Looking for "GPIO12 MTDI should be kept low at power-up" in esp32-wroom-32_datasheet_en.pdf

Looking for "GPIO5 strapping pin default pull-up" in esp32-wroom-32_datasheet_en.pdf

Looking for "GPIO15 MTDO strapping pin default pull-up" in esp32-wroom-32_datasheet_en.pdf

For U1, the datasheet confirms the required logic states at reset for these strapping pins, but it does not give a specific external resistor value. A standard, safe recommendation is 10 kOhm external pulls.

Recommended wiring for U1 strapping pins

Pin on U1Required reset state from datasheetRecommended resistorWiring
GPIO12 / MTDILow at power-up10 kOhm Generic ResistorGPIO12 -> resistor -> GND
GPIO5Default state is pull-up / 110 kOhm Generic ResistorGPIO5 -> resistor -> 3V3
GPIO15 / MTDODefault state is pull-up / 110 kOhm Generic ResistorGPIO15 -> resistor -> 3V3

Datasheet basis

PinDatasheet statement
GPIO12 / MTDIMust be kept low during power-up; MTDI=0 keeps VDD_SDIO at 3.3 V
GPIO5Strapping pin with internal weak pull-up
GPIO15 / MTDOStrapping pin with internal weak pull-up
Why 10 kOhm
  • The datasheet says strap states can be overridden with external pull-up/pull-down resistances.
  • Internal pulls are typically 45 kOhm.
  • 10 kOhm is a common strong-enough external value to dominate the internal weak pull and improve noise immunity.

Exact net intent

New resistor functionConnect between
Pull-down for GPIO12U1 GPIO12 and GND
Pull-up for GPIO5U1 GPIO5 and 3V3
Pull-up for GPIO15U1 GPIO15 and 3V3
If you want, I can next give you the matching fix for U6 as a short wiring checklist too.
CCS811 wiring checklist
Check missing pull resistors
Add resistor designators
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J1 SHIELD__3 - J2 P2
U1 EN - R5 P2
U3 VOUT - U1 VDD
U1 IO34 - J3 1
U1 SENSOR_VP - U5 A1
U1 SENSOR_VN - J3 2
U1
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Cow health-monitoring wearable PCB for a cow-mounted device. Rear strap electronics target 20-25 g and front sensing assembly target about 15 g. Uses an ESP32-based sensor controller, 200 mAh LiPo battery, battery charging circuitry, and interfaces for ammonia, methane, IR temperature, and saliva sensing. Design must tolerate moisture, mucus, debris, vibration, fur contact, and tongue/lick exposure while remaining compact and lightweight for wearable use.

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