WBA-TH1M

Module Features and Description

The WBA-TH1M Module makes it very easy to use Sensirion's SHT11 Digital Temperature/Humidity Sensor in your microprocessor controlled projects. The two-wire digital serial interface is simplified and sample code is available for several microprocessors.

My design is based upon an optimum circuit from experience with 3 different microcontrollers (Parallax Basic Stamp, Cypress PSoC, and TI MSP430). I wanted to design a module that would be very easy to use and could be extremely versatile without requiring any circuit modifications on the customer's part. My module can be used right next to a processor or at large distances with proper cable (Cat 5 or similar shielded cable). For a more reliable and bulletproof circuit that works directly with any microprocessor and without additional circuitry, I have included:

1) A pullup for the data line and pulldown for the clock line which keep these signals cleaner at longer distances. I have used this module with a 200+ foot stretch of Cat5 cable without any issues. Without these, that distance would be unreliable. The pulldown on the clock line reduces the possibility of sensor lockup due to clock variations. (The SCK pulldown resistor must be removed if the WBA-TH1M module will communicating on an I2C bus)

2) Inline protection resistors for the data line. This protects the processor and WBA-TH1M in case they try to drive the line into opposite states. Not all microprocessors include line protection on their IO pins. The inline resistor in the clock line is for increased stability of the clock signal since you can use such a wide range of clocking frequencies.

3) I used a 1uF cap so that apart from the desired noise reduction, it also reduces VCC ripple effects to the device.

Connections are made via a 4 pin 0.100" header as well as solder pads for wire attachment. There is a label on the back side that denotes the pinout. The module comes with a 4 pin right angle and straight header (unsoldered) to allow user versatility. This allows for top, bottom, and vertical mounting.

The module design allows for use of the Sensirion SF1 filter cap (if the cap's posts are removed) so that the sensor is IP67 rated for water, dust, and other contaminants for harsh conditions.

Modules are manufactured and inspected to IPC-610 specifications in an ESD controlled manufacturing facility. They are tested against a reference module under a 10 degree swing cycle.

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