As with most evaluation kits, I just couldn’t wait to find out what’s inside. In this blog, I’ll take the covers off the hub and sensor cube and look closely at the parts that make up the IDT SDAWIR03 demonstration kit.
The first device to be taken apart is the hub. The plastic case unclips by prying gently at the edges to reveal the internals.
It seems that IDT have designed their own “hat” for the Raspberry Pi that contains the ZWIR4512 module for communication with the cube. This module appears to be powered from the 3.3V line of the GPIO from Pin 1 and Pin 17, decoupled through C1 and C2. It seems C4 would have provided additional decoupling, but the part was not populated. Ground through Pin 39 is looped to the mounting holes on the right side of the board, which is commoned with Pin 34, 30, 20, 14 and 6 along the trace running along the top edge of the board to the ground plane on the left side of the board. The plane also contacts Pin 9 and 25, completing the communing of all ground pins from the hat connector.
Looking from the top, it seems clear that the header pins were hand-soldered to the board, with noticeable flux residue and some inconsistencies in soldering quality. The soldering is fine enough, but the board appears to be poorly manufactured. It is clear that there is a misalignment of the drill holes with the copper and solder resist layer during manufacturing, resulting in a rather strange-looking board. This kind of defect is not something I come across often, but on the antenna, it seems that any further misalignment may well cause a break in the printed antenna as the plated-through vias may break.
The printed antenna appears to have spaces for three matching components (ANT 1 – 3) but only ANT2 is populated with what appears to be an inductor or transformer balun.
The underside of the module carries the part number SENZWR001 REV01 with an FCC warning. There are also pads for mounting activity LEDs and resistors, but these are not populated. Also visible is the other “half” of the printed antenna. Four lines of the module are sent to the underside copper for connection – this appears to involve Pin 8, 10 (UART) and perhaps two GPIO lines (GPIO4/17 from my tracing).
The remainder of the hub is a Raspberry Pi Zero-W, revision 1.1. As someone who has never managed to get their hands on any variant of the Zero, it’s quite a handy small board. It is screwed into the rear of the casing.
The hat sits elevated above the board due to the height of the header connector, which allows for additional separation of the antenna from the board reducing interference potential. This is, however, bringing the board closer to the metallic labelling on the case, which may affect its sensitivity and range.
In case you were wondering, my kit came with a Sandisk Edge 8GB Class 10/UHS-I Class U1 card. This card is Made in China and is Sandisk’s commercial-grade card based on 3D NAND with improved endurance.
Next up is the cube, which sits in a clear plastic case that snaps together. The case is a little difficult to pry apart, with a tendency for the clips to snap back together. Starting from the low edge on the battery-holder side seems to make it easiest. The sensors plug into header receptacles on the board – take care to note the orientation as the board does not make this clear and plugging in the sensors backwards is not likely to end well. The board is then secured into the case with three Torx screws which need to be removed to liberate the board.
The board is marked IDT CONTROLLER BOARD V2.0. It appears the USB power enters through the microUSB connector where it is filtered and smoothed by L7/C12 before being regulated by U1 which appears to be a Texas Instruments TPS6220x high-efficiency SOT23 Step-Down DC-to-DC converter. Another regulator based on the same converter can be seen at U3, which perhaps may be responsible for the two CR2032 coin cell supply in the “stacked” battery holder that has somewhat dirty looking solder joints. A smattering of other support components and test-points are present on the board as well. There are two magnetic reed switches – one on the top and bottom which are used to put the module into reset/always-on modes.
The underside shows yet another regulator, U2, which may be responsible for the radio module’s supply (whereas the other ones may have been for sensor power, although I am not definitive about this). Further filtering of the USB power is provided by C7 and L4. A look at the pin wiring shows two pins on the sensor headers are just paralleled together – this appears to be the I2C SDA/SCL pins.
A close look at this board shows that it uses a different form of the ZWIR4512 module – this type is on a castellated PCB with external antenna connector. In this case, the connector is left disconnected, and instead, a chip antenna is installed at U5.
A look at the HS3001 humidity and temperature sensor board shows the bare minimum of components – just the sensor package with two bypassing capacitors is all that is needed. An optional R1 position is supplied, but its purpose is not known – perhaps for presence detection?
The FS2012-1010-NG flow sensor is rather more substantial. The sensor consists of a PCB with a 28-pin IC with the identification painted over – perhaps this might even be an LPC ARM microcontroller. Next to it is U4 which may be an opamp from Microchip. The sensor has plastic barb fittings on both sides, although flow is intended from P1 to P2 which is clearly marked on the rear. The J1 interface is marked on the silkscreening which includes an analog voltage output. The J2 interface doesn’t appear to be documented.
The IDT SDAWIR03 hub is built around a Raspberry Pi Zero-W with a custom-built “hat” utilising the surface mount ZWIR4512 module on a printed antenna coil. The module uses the UART for communication with the Raspberry Pi. The PCB appears to be poorly manufactured, with registration issues between the drill layer and the copper/silkscreen/solder-resist layer. The connector appears to have been hand soldered, although fairly well. The unit uses a Sandisk Edge 8GB microSD card for storage.
The sensor cube itself has an interesting board which seems to make a lot of use of the Texas Instruments TPS6220x high-efficiency DC-to-DC step-down converter. It also uses a different version of the ZWIR4512 module which has a castellated PCB with integrated antenna connector instead. The PCB utilises a more compact chip antenna instead of a printed antenna. The battery holder appears to be soldered a little roughly, but construction is otherwise compact and neat, with two reed switches serving to change modes or reset the cube.
The two sensors plug into the board, although the orientations are not clearly marked. The HS3001 has a very simple PCB which only features two de-coupling capacitors, whereas the FS2012-1010-NG features a more complex PCB with a 28-pin IC lacking identification and a number of other supporting components. The flow sensor uses barbed fittings to connect to a gas flow moving from P1 to P2. It has an unused analog output and a seemingly unreferenced J2 connector.
While the boards may be good for demonstration purposes, they do not appear to be tailored for easy development or modification.
This blog is part of the IDT SDAWIR Wireless Flow Rate, Humidity and Temperature Sensing Evaluation Kit RoadTest