Embedded Developer

A common problem in the IT world is to create a consistent environment in a repeatable manner. This is important in a number of use cases:

• Development
• Testing
• Training

This series of posts will investigate using Ansible to create a consistent test environment, one that can be setup and torn down quickly and easily.

The starting point is setting up the hardware and installing the operating system (OS) which will be covered here. Subsequent posts will use Ansible to configure the system and deploy additional tools.

The Hardware

The test environment will be based around the Raspberry Pi 5 (although any version of the Pi hardware could be used). The system will be built around the following components:

• Raspberry Pi (3, 4 or 5)
• 256 GByte SATA SSD
• SATA to USB adapter
• Cooling fan (for the Raspberry Pi 5)
• Power Supply
• Ethernet cable
• 3D printed mounts to bring everything together

Grabbing a Raspberry Pi 5 and putting all of this together yields something like this:

Raspberry Pi Setup

SATA SSDs have been chosen for the OS and data storage as they are both faster and more reliable than SD cards. From a cost perspective they are not too much more expensive than a quality SD card. It should be noted that recent third party addon boards are becoming available that add one or two NVMe drives to be added to the the Raspberry Pi 5 using the PCIe bus.

Write OS Image

The easiest way to create a bootable Raspberry Pi system is to use the Raspberry Pi Imager. This is a free tool that allows the selection of one of the many operating systems available for the Raspberry Pi and it can then be used to write the operating system to a SD card or HDD/SSD

The process starts by connecting the SATA to USB adapter the the SSD and then connecting the drive to the host computer. This makes the drive appear as an external USB drive.

Now start Raspberry Pi Imager:

Raspberry Pi Imager

Select the device we are going to create the image for, in this case this is the Raspberry Pi 5:

Select Device

The next step is to decide which operating system should be installed on the SSD. There are a large number of options and the selection will depend upon what you want to achieve. In this case we can use a basic system such as Raspberry Pi OS Lite. Firstly, select the Raspberry Pi (64-bit) operating system:

Select Operating System

Now refine this selection and select the Raspberry Pi OS Lite (64-bit):

Select Raspberry Pi Lite

A basic system will be adequate as the device is intended to be run headless and so the desktop environment and applications are not required.

Next step is to select the storage device that the image will be written to. Once this is done we can move on to providing some configuration options for the operating system.

Ready For Configuration

Click the Next button to move on to the next step, editing the configuration.

Edit Settings

Clicking Edit setting starts the editing process. The General options are presented first, here we can set the following:

• Hostname
• User name and password
• WiFi access point details

Customise General Settings

SSH should be enabled in order to run the system headless. This is enabled on the Services tab:

Customise Services

Clicking on Save now gives the option of applying the settings and start writing the image to the SSD:

Apply Settings

The final step is to verify that the SSD can be erased:

Confirm Media Erase

Control now passes back to the main window where the write and verification progress can be monitored:

Writing OS

After a short while the the process will complete and Raspberry Pi Imager wil conform that the image has been written successfully and the drive can now be disconnected from the host computer and connected to the Raspberry Pi 5:

OS Write Successful

Conclusion

The whole process of creating the image is straightforward and only takes a few minutes. At the end of the process the Raspberry Pi is ready to boot.

The next step will be to start the installation and configuration of additional software tools and components. Something for the next post in this series.

Most of the PCBs I make have mounting holes in the final layout to allow the boards to be firmly attached to 3D printed cases or mounts. When I first started using KiCAD I found it difficult to position the arc edge cuts around the mounting holes accurately. This was not too critical but it was a little annoying. The error in positioning the arcs was minor and is difficult to see but it would be good to fix the problem.

This was something I finally worked out in the last design I sent to manufacture and thought it would be something others might want to know about.

Board Layout

Most of my designs usually result in a square or rectangular board. The boards are simple and don’t really need to fis an irregularly shaped case. So most of the time I am trying to place a hole at the corner of say a square and then place an edge cut around the hole, something like this:

PCB with two mounting holes

Placing the mounting holes is a simple case of editing the x and y positions of the mounting hole and ensuring that the holes are lined up correctly. The edge cuts are a little more difficult to position consistently when placing them by hand.

Accurate Edge Cuts

As noted above, the first stage is to place the mounting holes on a rectangular grid and using the x and y positions to place the holes. Next step is to create an arc centred on one of the mounting holes with the appropriate radius. This can be done in using the centre of the mounting holes as the starting point and then sweeping an arc through 90 degrees around the hole:

Arc and Hole

Next up we duplicate the arc, rotate it through 90 degrees and move to one of the opposite mounting holes:

Duplicated arcs

As you can see, the duplicated arc is not centred on the opposite mounting hole. We now use the positioning tools to align the arc with the mounting hole. Start by selecting the arc and then right click to bring up the context menu and select Position Relative To… from the context menu:

Positioning context menu

From the positioning dialog click on the Select Item button:

Select item button

Next, select the reference item, in this case it is the mounting hole:

Select the reference item

The positioning dialog will now reappear with the reference item selected. Ensure that the Offset X and Offset Y are both set to 0 and click OK.

Position dialog box

The arc should now move and be centred on the mounting hole.

Final arc position

Finally, repeat for the remaining 2 mounting holes.

Conclusion

This method allows for the board outline to be defined more accurately then lining up the arcs by eye. It is simple to do and only takes a few minutes to complete. The arcs can then be used as the anchors for the linear edges of the board.

This technique is also useful for positioning other parts on any design.