TIRF

TIRF is the actual hardware of NetBrows. Since the project has been divided into different parts, TIRF now has its own page.

The module mainly consists of three components:

1. The microcontroller, which enables the other components and the calculator to communicate.

2. A microSD card as a memory extension.

3. The rf module to establish wireless connections between different modules.

The following images show the components:

The controller is an ATmega644 of the AVR microcontroller family manufactured by Atmel with 64kiByte program memory, 4kiByte RAM and 2kiByte EEPROM. Although that may look very small, it can contain quite much code. Of course, you can't program like on a PC with plenty of performance and memory, but with some practice, it works quite well.

The clock source for the controller ist the internal 8MHz RC oscillator, so there is no need for an external crystal. It's not accurate, but because we don't use any interfaces running asynchronously such as RS232, that's not really a problem.

Another important design consideration is the power consumption of the whole module due to the fact, that it stays powered even if the calculator is off. By disabling all peripherals of the controller and interrupting the power supply to the SD card, the module now draws no more than a few microamperes in sleep mode.

The SD card has been directly soldered on the PCB. Of course, it is also possible to attach a second PCB with a mounted slot so the card can be removed or inserted without any trouble. You can use any SD card (Whether standard, mini or micro doesn't matter), but it doesn't make sense to attach a card with several Gigabytes of capacity due to the relatively slow interface with a few kilobytes of data per second.

The last component, the rf module, causes some problems at the moment. It's the TRW-24G manufactured by Wenshing. One problem is how to get them: We were able to order eight modules together with others, but there doesn't seem to be another ordering in the near future due to too little interest. The other problem concerns the range which is at the moment no more than about one meter. Maybe this is caused by the sandwiched construction of the module. Further tests to improve this are planned.

The schematic as well as the firmware are fully open source, feel free to use it for your own projects.