0x06: 16 ch thermometer, OneWire Interface

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Background

The most frequently measured parameter in industry is temperature. Typical implementation of temperature measurement in large, stirred vessels usually comes down to a handful of Pt-100 platinum temperature transmitters, since each measurement point cost good money and gradients are assumed to be absent. This approach is highly criticisable, if you have basic insight into sampling theory and/or fluid dynamics. You will need cheap, precise sensors to effectively conquer the heterogeneous nature of virtually any unit operation. And plenty of them.

The DS18B20 temperature transmitter from Maxim Integrated has been around for more than a decade. It features several interesting functions that are well-described in the datasheet and on numerous internet fora. Being factory-calibrated, having a unique MAC-address, having built-in CRC generator, and its ability to draw power from the data line are some of the key selling points.

Function

This PCB conveniently allows you to connect up to 16 pcs. DS18B20 temperature transmitters to a OneWire bus adaptor, e.g. the DS9490 USB interface. A linear regulator (78M05) provides auxiliary power if the data bus is not able to drive the transmitters satisfactorily via the so-called parasite power mode. The board is also populated with a four channel analogue-to-digital converter (DS2450) giving you four voltmeter channels (0-5 VDC) that are broken out to the terminal block connector.

The 18 channel jumper block allows the system power to be cut and each dataline from the DS18B20’s as well as the DS2450 to be disconnected from the OneWire bus.

Disclaimer

This design does not comply with the official guidelines from the OneWire community with respect to network topology. Based on my own personal experience, these transmitters are extremely robust and thanks to the built-in CRC in each DS18B20, measurement errors seldom/never occur even in an industrial setting. Comments for improvements to the design are welcome. Please use the form on the Contact page.

License terms
The 0x06 design is published under the Creative Commons Unported 3.0 License.  I do not profit from this design, neither should you. You are welcome to adapt, modify, and redistribute this design as long as the license terms are respected.

Physical size of PCB

100 mm (width) by 50 mm (height). Double-sided.

Rendering and photos

0x06rev1_3d_rendering

DipTrace 3D rendering without connectors

0x06_back

Photo of the PCB backside

0x06_assembled

Photo of the fully assembled PCB

0x06_DUT

Photo of a test setup with DS9490 USB interface and four DS18B20 sensors connected

0x06_DS18B20_wiring

Photo of the DS18B20 wiring/connection to the wafer connector. Red: VDD, white: data, silver: GND

 Bill of materials

1 pcs. 78M05 linear voltage regulator, 5 VDC, 500 mA, TO-252 (SMD)

1 pcs. DS2450 quad A/D converter, SOIC-8 (SMD)

16 pcs. DS18B20 on cable fitted with three-way connector

1 pcs.  4k7, 5 % resistor, form factor 1206 (SMD)

1 pcs. 1k, 5 % resistor, form factor 1206 (SMD)

2 pcs. 100 nF ceramic capacitor, form factor 1206 (SMD)

1 pcs. diode bridge, form factor DBS (SMD)

1 pcs. 220 uF, 16 V electrolytic capacitor, form factor 8.3 mm by 8.3 mm (SMD)

1 pcs. light emitting diode, form factor 1206 (SMD)

18 pcs. two-row pin header

18 pcs. jumper

16 pcs. three-pin wafer connector

4 pcs. three-way terminal block connector

1 pcs. DS9490 OneWire to USB interface or another type of interface, e.g. an MCU

Estimated cost

DS18B20 temperature transmitters can be procured from China via eBay. A transmitter with 3 m cable will not cost more than EUR 5,-. A complete system using all 16 channels and the four ADC channels will be around EUR 90,-. Possibly less, if you buy DS18B20 transmitters with shorter cable (e.g. 50 cm). You could also make the cables yourself. The DS9490 USB adaptor costs no more than EUR 30,- and will allow you to connect to a large (unlimited) number of OneWire devices.

Downloads

DipTrace v. 2.4 PCB design file: 0x06rev1 DipTrace PCB

Gerber files: 0x06rev1 Gerber

DS18B20 OneWire temperature transmitter datasheet: DS18B20

DS2450 OneWire quad A/D converter datasheet: DS2450

DS9490 OneWire to USB interface datasheet: DS9490R

Links

Maxim Integrated’s OneWire website

Maxim Integrated’s OneWireViewer

The OneWire Filesystem website

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