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<img> http://www.sbprojects.com/projects/saa1064/69113491.gif </img>

See, I told you it only uses a few components. The heart of the circuit is of course the SAA1064, which is made by Philips. It is operated in the so called dynamic mode, which means that the two 8-bit outputs of the chip can drive four 7-segment displays in a multiplexed mode.

We need two transistors to alternately switch between displays 1 and 3 or displays 2 and 4. In my case the module is equipped with two SMD type transistors BC817-25, which can be substituted by any transistor with similar properties.

C01 is used to decouple the power lines. And C02 is used in an oscillator which generates the multiplexing frequency. You can measure a triangular shaped waveform of about 2.2V p-p @ 18kHz on pin 2 when the chip is operating in multiplexed mode. This frequency is internally divided by 128 to produce the multiplex frequency of approximately 140Hz.

R01 and R02 are connected to the I²C bus.

By the way, you probably figured out already that the displays are of the Common Anode type.