Added the last few LEDs, got the firmware working on the Tiny2313. Added a socket for a Tiny13 for ADC input. Here's how I get the data to the display. The driver chip (2313) sends clock pulses to a counter on the ADC (Tiny13). The counter is set to do PWM using the latest reading from the ADC. When the counter overflows an interrupt fetches a new ADC reading. The PWM output is set high. As the clock form the driver chip comes in the counter increments. When it matches the ADC reading the PWM output goes low. On the Tiny13 I just have to configure the timer and copy the ADC value in the overflow.

The driver software is a little more complicated, but not much. Part of the main loop toggles the clock line to the Tiny13 counter. When the PWM line goes high I reset, then just count the clocks until it goes low. When that happens I copy the count and arrange to display it. The clock to the Tiny13 counter isn't regular, it can go faster or slower, but it works anyway.

I put a piezo speaker on the clock line to verify that I had it working. Then I put it on the data return line and listened to that. With the PWM you can hear differences in the ADC reading.

Next time I want to build on a custom PCB instead of the project board. Maybe I'll make all the LEDs the same color as well.

7x5 LED Array on flickr.com.