Franzininho tiny

The Franzininho project has already impacted several people in Brazil through soldering activities and programming of a DIY-style board. The first board, Franzininho DIY, based on the ATtiny85, allowed several people to have the first contact with the soldering of an electronic board and in the end, they could program it directly in your computer and create applications. The project had a very nice acceptance by the Brazilian maker community. The open hardware project, following the good practices of open hardware projects, has extensive documentation, enabling people to study, assemble, modify and even sell. With this strength, we have been able to assemble many boards through Brazil, I believe that more than 2000 board have already been assembled since 2017.

Now is the time to go up another step in the development of the Franzininho project. The Franzininho DIY board has the objectives of encouraging people to build their own hardware projects, through component knowledge, assembly and then programming. Now, we are working on the Franzininho tiny, the new board to be part of the Franzininho family. A board aimed at exploring programming and applications with an 8-bit microcontroller.

The ATtiny microcontroller has been chosen that maintains compatibility with Franzininho DIY (ATtiny85-based), but now the board coming assembled and ready to use.

Franzininho tiny is an open source hardware board. The following are the details of the hardware project, which is in the test phase and being developed.

Hardware

As mentioned above, for the Franzininho tiny I chose the microcontroller ATtiny841.

ATtiny841 provides the following features:

• 8K bytes of in-system programmable Flash
• 512 bytes of SRAM data memory
• 512 bytes of EEPROM data memory
• 12 general purpose I/O lines
• 32 general purpose working registers
• One 8-bit timer/counter with two PWM channels
• Two 16-bit timer/counters with two PWM channels
• Internal and external interrupts
• One 10-bit ADC with 5 internal and 12 external channels
• One ultra-low power, programmable watchdog timer with internal oscillator
• Two programmable USARTs with start frame detection
• Slave Two-Wire Interface (TWI)
• Master/slave Serial Peripheral Interface (SPI)
• Calibrated 8MHz oscillator
• Calibrated 32kHz, ultra low power oscillator
• Four software selectable power saving modes.

The ATtiny841 is available in SMD packages and the SOIC for the board has been chosen. The following figure shows the pinout of the microcontrollers with the capabilities of each pin:

With this microcontroller, the Franzininho project now can explore more applications due to the number of I/O pin (compared with ATtiny85) and more serial communication resources.

The choice of this microcontroller was due to the compatibility with the applications made for the Franzininho DIY board and the attiny841 features.

In addition to the applications made with Arduino libraries, it is intended to explore the programming of microcontrollers in C language and assembly with the purpose to teach about architecture.

Schematic

The following figure shows the schematic of the Franzininho tiny board:

Printed Circuit Board - PCB

The Franzininho tiny board was designed with all SMT components. As the purpose of this board is in the study of programming and final applications, I decided to make a form factor compatible with protoboard, which facilitates studies on the bench and also for standard boards. The following figure shows the layout made in Kicad:

The following figures show the 3D model of the board generated in Kicad:

Board

Hardware License

Like Franzininho DIY, the Franzininho tiny board was also published as an open hardware project. For this board was chosen the CERN Open Hardware License, a more appropriate license for hardware projects.

As defined in the how-to guide document, the following files are included in the project repository:

• LICENSE.TXT
• cern_ohl_v_1_2_howto.pdf
• CHANGES.TXT
• COPYRIGHT.TXT
• PRODUCT.TXT

For project replication or derivations, please check the license requirements and best practices.

Software

As bootloader was chosen the micronucleus, a light bootloader, made for the attiny family. The board is compatible with the Arduino IDE, making the appropriate settings. I'm working on a package for IDE integration.

Conclusion

The Franzininho project continues its mission, now with a new board will enable more people to learn about microcontroller programming and put their ideas into practice. This board has no objective to compete with Arduino or compatible Arduino boards already on the market, but to build a collaborative hardware project in Brazil. Through a simple design, we can learn several skills.

The project is still in beta testing and there is a long way to go. All feedback is important for the development of the project, as well as contributions in software, hardware, and documentation.

Feel free to make your own Franzininho tiny board. The board is available in OSH Park and you can view the BOM on Octopart.