BalenaFin – A Raspberry Pi Compute Module Carrier Board

The BalenaFin is a professional carrier board for the Raspberry Pi Compute Module. It eliminates the need for developing a custom carrier for the end application and helps accelerates the products development and time-to-market which is very critical for any product’s success.

There are also other carrier board options available but Balena has the best features which would serve most of the requirements well (IMHO).

What are the advantages of using BalenaFin Carrier Board?

Let me share first what I really loved about the BaleanFin V1.1 Board, which makes it power-packed carrier board for raspberry pi compute module (Raspberry Pi Compute Module CM3 Lite & CM3+ Lite).

1. Small Form-Factor

Given the vast feature-set available onboard, the form-factor of the board is really small (91.81 x 91.36 mm). As mentioned above there are other options available in the market when it comes to the carrier board for the Raspberry Pi Compute Module but I did not find any other board any close to what BalenaFin V1.1 has to offers, be it features, flexibility and the cost.

There is one more board, My Pi Industrial Integrator Board which is also good but I am yet to complete my detailed review. My quick review revealed it has fewer features on standard board, bigger in size (125 x 142 mm), more expensive, documentation and support is not as good as of Balena. (NOTE: This review is still work in progress)

2. Availability (till 2024)

Although 7-year is the minimum I recommend when picking up an off-the-shelf board, but 5-year commitment is still good as the development time from the hardware side is drastically reduced with this ready board.

I would suggest, Balena should state how they will handle the situation in case this board is getting obsolete and customer needs to support their existing customers (repair, replacement). Possible options could be:

• They can share the design files which eliminates the risk.
• They can commit if they will be coming up with a compatible board if the V1.1 is going obsolete.
• 12 – 18 months notice to the customers before going EOL, so they can buy some stock and make their own arrangements.

3. Onboard eMMC

SD card corruption issues don’t come into the picture and as it is assembled on the PCB so vibration has no impact. BalenaFin V1.1 Board has option to chose 8GB, 16GB, 32GB or 64GB Industrial eMMC storage while ordering.

4. Wide Power Supply Voltage Input

BalenaFin board supports 6-24V DC input. It provides two input connectors, one is Round-jack DC Pin and other is a 2-Pin terminal.

5. USB on a 4-Pin Header

This is a challenge when using a typical SBC (example Raspberry Pi 3), if you need to connect a sensor or a modem or another USB based card, you don’t have an interface to connect, the only way it provides is via USB-A external connector, which is not recommended way for the production. 4 Pin USB Port on a header is a great option.

6. Onboard Low-Power MCU

When working with an application processor running an OS like Linux, for many interesting applications the real-time capability not available & high power consumption could be an issue. The low-power M4 MCU helps hugely. The IO from this MCU is available on the header, that’s great.

7a. Onboard Connectivity Options (WiFi, BLE, GSM/GPRS)

BalenaFin offers dual-band WiFi module & BLE which makes it ready for most IoT applications. Mini PCIe Socket is available in case GSM/GPRS connectivity is required or to use other mini PCIe based modules. Nano SIM Connector is readily available so no need to create a custom board.

7b. Option for an External Antenna

This is quite an important option when working on industrial applications. With an external antenna, one can get better TX power efficiency & RX sensitivity.

8. IOs for Extension

40 pins Raspberry Pi Hat header & 18-Pin Co-processor header gives the flexibility to the developer to use other HATs or create their own custom add-on boards as per their application requirements.

9. Temperature Range

Operating temperature range for BalenaFin Board is -25 to 70 degree C which is quite good for most of the applications.

10. Ready option for the Enclosure

This greatly help customers as a starting point. If the design could be open-sourced it will be really good.

What could have been improved in BalenaFin Carrier Board?

Some of the features, I think could have been provided (my wishlist):

1. HDMI & Power Supply connectors could have been on the same side as USB & Ethernet.
2. One/two LED indicators could have been brought near USB/LAN connector and exposed via enclosure for indication.
3. Power supply connector ORing diodes could become an issue due to voltage-drop and hence heating. It can lead to heat built-up and associated reliability or performance issues. Power Supply round-jack connector already provides a selection using its 3-pin connection. The connection could be made like if the power supply cable is not connected, it will connect the power from 2-pin terminal else power will come from the jack.
4. For reverse-voltage & over-voltage protection, may be a P-MOSFET based circuit or OV protection ICs could be used which will not have diode voltage drop issue and incase input voltage goes higher than the voltage circuit is capable of, the fuse (+TVS will be there in parallel) will blow.
5. Independent & dedicated hardware WDT would have been a good option to govern Raspberry Pi & low-power MCU software hang conditions. For high reliability application this might need to be implemented using add-on custom circuit.
6. Studs/stand-offs – this is very critical for fastening the module. Vibration can lead to module coming off the SODIMM connector, I have seen this practically happening. With proper stud/standoff in place, the module becomes firm and also becomes more rigid in case bigger heatsink/enclosure needed be attached with little pressure. Without standoff heatsink pressure could push module inside making heat-sink bonding ineffective.  
7. How to replace SIM in the field if one network provider does not have the signals in a particularly remote area? Consider, the customer had no idea of signal issues when sending the device to the field. Opening the enclosure need to be avoided at all times in the field.
8. Like SIM, replacing RTC battery & Fuse is not possible once the enclosure is closed. This is a challenge as in few years RTC battery could drain or some fault can occur, similarly, fuse may blow. Balena could make RTC, Fuses, SIM available on the bottom side of the board(or on a side) and provide an appropriate opening in the enclosure. This could greatly help customers in the field.
9. Local memory for storage (FRAM, EEPROM, SPI Memory). Mainly SPI memory, I would say is important for data logging applications. Storing periodic data (at a faster rate) on eMMC could lead to memory issues/wear-tear. SD card (accessible from outside in the enclosure) option could also be provided by default. It is always a good idea to avoid writing data (mainly in the application where data is logged or stored regularly) on the same storage where the OS resides to avoid corruption issues.

For a company involved in building professional boards for commercial and industrial applications, documentation & support becomes the key factor which drives success. Great documentation helps reduces support load and brings customer delight as they get most of the information they were looking for without even asking :).

Some of the documentation improvements, I see could be done are:

1. Power consumption statistics could be added. Showcasing, from a power consumption point of view what’s possible with BalenaFin board would be great deal for a potential customer.
2. List of example IO board should be easy to find. Some of the tests which are already carried out could be shared. Similarly, documentation on tested options for Mini PCIe cards would be very handy.
3. Heat sink recommendations, some tested examples could have been better + a Metal base of the enclosure for high computing requirements.
4. BalenaFin board schematic, 3D models are not easy to find.
5. How to program and work on internal MCU, ready examples would be much better. There is Github repository available but navigation & the whole structure of the documentation could be improved greatly. Some common use cases could be given in an article form.
6. In the datasheet, documentation of alternate functions of all IOs on the headers should be given so customer need not to go anywhere searching for this information.
7. Hardware roadmap / OS improvement roadmap could be made available on the website.

If you are considering to use BalenaFin board, I hope the information provided above will help you take an informed decision.

There are basically few main parameters which needs to be considered when selecting an embedded board for your product development i.e long term availability, temperature range, support/documentation, flexibility, scalability.

Also, it would be a good idea to learn advantages & some limitations of using Raspberry Pi compute module for your product development.

If you like the article, please share it with others. Any suggestion or comments, let me know here. Read my other articles on embedded system design.

Happy learning to you!