Low Cost Implementation

For cost sensitive applications with high tolerance on accuracy, a solution utilizing the internally calibrated RC Oscillator of the ATtiny28 could be used. The high current drive capabilities of PA2 can sink the LED directly giving a solution with only a few external components as shown in the figure below.

Figure 1. Low Cost RC5 Transmitter

By using an external resonator and a driver circuit for the IR LED, a more flexible solution is achieved. The main advantage is higher driver capabilities and higher frequency stability over voltage range. If however the receiver is self-synchronized, it will adapt to the changing frequency of the transmitter, and a solution using the internal RC Oscillator could be used with good results.