Parallax Inc. 28018 Humidity and Temperature Sensor - Equivalent & Substitute Parts

Part Overview

The Parallax Inc. 28018 is a combined humidity and temperature sensor module designed for I2C digital output applications. This component measures relative humidity across the full 0 to 100% RH range with ±3.5% RH accuracy and simultaneous temperature sensing. The device operates from 2.4V to 5.5V supply voltage and features a 5-second response time, making it suitable for environmental monitoring and climate control applications requiring through-hole mounting.

The Parallax 28018 is classified as obsolete. Identifying functionally equivalent substitute components is necessary to support ongoing system maintenance, design updates, and procurement continuity when original inventory becomes unavailable.

Substiute Parts

28018

Parallax Inc.In Stock: 93428018 Datasheet

Current PartRFQ

HIH7120-021-001

Honeywell Sensing and Productivity SolutionsIn Stock: 7872HIH7120-021-001 Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the Parallax 28018 is determined by the following critical parameters:

Primary Compatibility Criteria:

• Sensor functionality: Combined humidity and temperature measurement
• Output interface: I2C digital communication protocol
• Humidity measurement range: Full 0 to 100% RH span
• Supply voltage overlap: Minimum 2.4V to 5.5V operating range
• Mounting configuration: Through-hole package type
• Accuracy specification: ±3.5% RH or better

Secondary Compatibility Considerations:

• Response time: 5 seconds or faster
• Output resolution: 12-bit or higher
• Moisture sensitivity classification: MSL 1 or equivalent

The Honeywell HIH7120-021-001 meets all primary compatibility criteria. This substitute provides I2C output, measures humidity across 0 to 100% RH, operates within the required voltage range, and uses through-hole mounting. The substitute demonstrates improved accuracy (±3% RH versus ±3.5% RH), higher output resolution (14-bit versus 12-bit), and active product status with full environmental compliance documentation.

Parameter Comparison

Engineering Selection Recommendations

Substitute Viability: Honeywell HIH7120-021-001

The Honeywell HIH7120-021-001 is a functionally equivalent substitute for the obsolete Parallax 28018 based on electrical and mechanical parameter alignment. Both components provide I2C-based humidity and temperature measurement across the 0 to 100% RH range with through-hole mounting configurations.

Advantages of the Honeywell substitute:

• Active product status ensures ongoing availability and manufacturer support
• RoHS compliance and REACH unaffected status provide regulatory documentation
• Improved accuracy specification (±3% RH) exceeds the original ±3.5% RH requirement
• Higher output resolution (14-bit) provides enhanced measurement granularity
• Extended lower voltage limit (2.3V) offers broader supply compatibility

Design Consideration: The Honeywell HIH7120-021-001 uses a 4-SIP module package versus the Parallax 28018's 8-DIP module package. This difference requires PCB layout modification and pin configuration verification during integration. Pin-to-pin functional mapping must be established based on I2C protocol requirements and supply voltage connections.

Compliance Status: The Honeywell substitute carries RoHS compliance certification and REACH unaffected status, supporting modern procurement and environmental compliance requirements.

Frequently Asked Questions (FAQ)

Q: Can the Honeywell HIH7120-021-001 directly replace the Parallax 28018 without PCB modifications?

A: No. The Parallax 28018 uses an 8-DIP module package while the Honeywell substitute uses a 4-SIP module package. These are different physical form factors requiring PCB layout changes. Pin assignments must be verified against each manufacturer's datasheet to ensure correct I2C signal routing and power supply connections.

Q: Are the I2C communication protocols identical between these two sensors?

A: Both components use I2C digital output. However, register maps, command structures, and data formatting may differ. Firmware or software modifications may be required to accommodate the Honeywell device's 14-bit output resolution compared to the Parallax 28018's 12-bit resolution.

Q: What is the impact of the 1-second difference in response time (5 seconds versus 6 seconds)?

A: The Honeywell substitute has a 6-second response time versus the Parallax 28018's 5-second response time. This 20% increase is generally acceptable for environmental monitoring applications. Applications requiring sub-5-second response characteristics should evaluate this specification against system requirements.

Q: Does the Honeywell substitute operate across the same voltage range?

A: The voltage ranges overlap substantially. The Parallax 28018 operates from 2.4V to 5.5V, while the Honeywell HIH7120-021-001 operates from 2.3V to 5.5V. The Honeywell device provides an additional 0.1V lower operating margin. Both devices are compatible with standard 3.3V and 5V logic supply systems.

Q: What certifications does the Honeywell substitute carry?

A: The Honeywell HIH7120-021-001 is RoHS compliant and REACH unaffected. The Parallax 28018 specifications do not include these compliance certifications. For applications requiring regulatory compliance documentation, the Honeywell substitute provides superior certification coverage.

Q: Is the improved accuracy of the Honeywell device (±3% RH versus ±3.5% RH) significant?

A: The 0.5% RH accuracy improvement represents approximately a 14% reduction in maximum measurement error. For precision environmental monitoring, HVAC control, or calibration-sensitive applications, this improvement may be operationally significant. For general-purpose humidity sensing, the difference is typically negligible.

Q: How does the 14-bit output resolution of the Honeywell device compare to the 12-bit Parallax output?

A: The Honeywell device provides 4 additional bits of resolution, resulting in 16 times finer measurement granularity. This translates to approximately 0.006% RH per LSB for the Honeywell device versus 0.024% RH per LSB for the Parallax device. Applications requiring high-resolution humidity trending benefit from this improvement.