An ESP32 board intended for use with TL-136 level sensors
Version 1 was built and is running well.
The sensor officially requires 24V, but in practice it runs well down to about 7V. An op-amp is used to limit the current through the sensor and protect the ADC in case of a short-circuit. The bias current of the op-amp has a small but measureable effect, however the voltage measured by the ADC is still very linear to the current through the sensor.
The board can be used with ESPHome, see esphome.yaml for an example configuration.
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1x TL-136 differential pressure level sensor
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1x ESP32-WROOM-32x, can be any variant with the same footprint
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1x MCP3421 ADC converter
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1x OP07 Operational Amplifier
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1x MCP9700B temperature sensor (optional)
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1x DC-DC module with 780x compatible pins and 3.3V output. Must support 12-18V input
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MLCC capacitors 0603, X5R or X7R, at least 6.3V
- 5x 100nF (C1, C2, C3, C5, C6)
- 1x 1µF (C2)
- 2x 10µF (C4, C9)
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MLCC capacitors 0603, X5R or X7R, at least 25V (better 50V)
- 1x 100nF (C7)
- 1x 1µF (C8)
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1x Polymer capacitor 5.0mm, at least 6.3V, 22µF (C10)
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1x Polymer capacitor 6.3mm, at least 25V (better 50V), 10µF (C11)
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1x Bidirectional TSV diode, SMA, voltage slightly above max. supply voltage (D1, optional)
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1x Pin header 0,1" 1x3 Pins (J3)
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1x BSS84 P-Channel Enhancement MOSFET (Q1)
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8x Resistor 0603, 10kOhm (R1, R3, R4, R9, R10, R11, R12, R15)
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2x Resistor 0603, 47kOhm (R2, R13)
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3x Resistor 0603, 1kOhm (R5, R6, R7)
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1x Resistor 0805, 100Ohm, high precision (R8)
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1x Resistor 0805, 33Ohm (R14)
Optional pin headers are omitted. They are intended for later reuse of spare PCBs.
The enclosure is an RL6115 from Hammond Manufacturing.
- Made more room for DC-DC module, it was a tight fit next to the capacitors
- Rotated TSV diode so that silkscreen is correct for unidirectional diodes
- Changed temperature sensor from MCP9701 to MCP9700B, changed footprint from SC70-5 to SOT23-3
- Some cosmetic fixes
- Marked optional stuff as DNP