I added the last three LEDs to my 7x5 display awhile back, but didn't actually test them until this morning. One of them wasn't lighting up. Took a close look and I can see what a poor solder job I did. The flying wire wasn't even touching the next on in the row. Have to fix that next time I get the iron out.

I want to try out the bidirection LED thing using this board. I want to read all seven LEDs in the rightmost column and see which one you are touching. For starters I'll just light up the whole row, so you can see a moving bar of lights when you run it. Eventually you could use this to set a value: the center line is no change, each row higher means increase faster, each row lower means decrease faster. Or, from top to bottom: +++ ++ + 0 - -- ---.

To get started I created a new project in Atmel Studio for the Tiny2313 chip. This time around I'm not using the overflow interrupt for timer0, I'm just polling the overflow flag and resetting it. It didn't take long to get a row-strobe test pattern running. I've added sockets for ISP to the board, so I can just build the software and then upload it without disconnecting anything or removing the chip from the board. Sure makes things easier.

I should save off a copy of the current firmware, it's nice to have a test pattern to make sure all the LEDs are lighting up. That's how I found the bad solder joint this morning.

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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.

I'd like to build a device that allows you to put in say an 8 digit number and it returns a strong password (or a less-strong password for places that don't accept !@#$%^&* etc).

I put into the firmware my own personal 'munge factor', so I can put the number into a 'password hint' field and use that when I forget the password.

This would use probably a Tiny2313 or a Mega8, an LCD display and a few push buttons for input. A salt factor is stored in the EEPROM.

Yeah, I have a problem remembering passwords.