How to use Flex-PCBs from Evaluation Kits in Prototyping
April 22, 2021 by Johannes Winkelmann
Sensirion’s evaluation kits for SHT and SGP sensors come with sensors on a Flex-PCB, that can be combined with our SensorBridge hardware and ControlCenter evaluation software for component level evaluation, without the need for any programming.
When the goal is to move to a prototyping stage, a number of third party companies like Adafruit, Sparkfun, Mikroelektronika, Pimoroni or Seeedstudio offer convenient breakout boards to connect our parts to development kits quickly and safely. In this article, we will present an alternative way by using an interface PCB to reuse the sensors on Flex-PCB, which can be especially helpful for parts that are not readily available on PCBs.
Precaution
The method presented in this article assumes that the supply and logic voltage levels between the development kit and sensors used matches; before you recreate this setup, please double check that this is the case for your setup as well, as too high supply voltages can damage your sensors irreparably.
Hardware Setup
Required material
For this example, we will be using the following hardware components:
- Arduino MKR 1010
- Sensirion SHTC3 Relative Humidity and Temperature Sensor on Flex-PCB
- Adafruit Touch Screen Breakout Board for 4 pin 1.0mm FPC (https://www.adafruit.com/product/3575)
- Four jumper wires, female to male (e.g. https://smile.amazon.com/EDGELEC-Breadboard-Optional-Assorted-Multicolored/dp/B07GD25V8D/)
The key ingredient here is the “Touch Screen Breakout Board”, which is originally made to interface with a Flex-PCB but which shares the connector format with Sensirion’s sensors on Flex-PCB.
Note: the Arduino MKR1010’s VCC and logic levels are at 3.3V, and the SHTC3’s supply voltage is from 1.7..3.6V; as mentioned above, it is important that those voltages are compatible.
Connection Guide
Step 1: Connect the sensor to the breakout board
To connect the SHTC3 with the breakout board, pick up the sensor on flex with the component facing you, and carefully push it into the connector socket on the touch screen breakout board. The result will look like this:
Step 2: Connect the breakout board to the Arduino
The pinout is as follows:
| Pin on breakout Board | Label on breakout board | Function |
|---|---|---|
| 1 | X- | VCC |
| 2 | Y+ | SCL |
| 3 | X+ | GND |
| 4 | Y- | SDA |
To connect these to your developer kit, connect the pins from the “Function” columns with the corresponding pins on your board. For the Arduino MKR, the following pins are used:
| Function from sensor | Label on breakout board | Label on Arduino |
|---|---|---|
| VCC | X- | VCC |
| SCL | Y- | SCL |
| GND | X+ | GND |
| SDA | Y- | SDA |
Important: make sure the VCC output from your board matches the supported voltage range of the connected sensor.
Software Setup
For the software, we will use the official ‘arduino-sht’ library, the can be found in the library manager of the Arduino IDE. If you don’t have the Arduino IDE yet, you can download it from https://www.arduino.cc/en/main/software. To install the ‘arduino-sht’ Library, select “Tools” > “Manage Libraries”, and select the entry that is named “arduino-sht”; as shown below:
Test
Now that the software is installed, we’re ready to start testing. For this, follow the following steps:
- Connect your Arduino to your development computer
- Select the correct Arduino board under “Tools” > “Board”, in the case of this example the MKR 1010
- Select the serial port your Arduino is connected to
See screenshot below how this could look. Note that the serial port can have a different number and even format, depending on your setup and operating system.
Finally, open one of the RH/T samples from “File” > “Examples” > “arduino-sht” > “sht-autodetect”, then hit the “Upload” button (or choose “Sketch” > “Upload”), to compile and flash the program, and finally “Tools” > “Serial Monitor” to display the output. The serial monitor should now display humidity and temperature data, like this:
