Saturday, August 28, 2010

Step4x16 addressing test

Not much new to report but it is so much fun to see your project actually make something visible and audible happen :)

I have tested the address decoder and data latch mask logic. A small video clip was made as well just to show the amazing LEDs :P

Boards and content
I will not build the entire board using bread boards, of course, but I had to test the basic addressing I am going to use before doing the PCB design.
There is nothing new on the upper board, still only the PIC, opto-coupler and DAC.
On the lower board I have a 4-16 decoder (left edge) which acts as an address decoder using 4 pins of PORTA on the PIC. Another pin from the PIC is used as Data Latch when writing.
This latch, together with the decoded address is put through a NOR-gate (second chip from the left) to send the latch pulse only to the correct chips.
In this case, the correct chip is the 4-16 decoder/latch (third chip just before LEDs).
The decoder/latch directly drives the step LEDs which indicate the current step of the sequence being played. Since only one LED is active at a time I only need one current limiting resistor instead of 16, and the chip has no problem driving an LED. I'm using a 330 ohm resistor a.t.m. so it's probably less than 10mA).

Sequence and demo
The sequence contains a few steps that extend into the next one, thus creating longer notes. Sometimes the pitch is changed without retriggering, which seems to work nice (although I already discovered that by mistake last time).

In the clip below you can see the old bread board together with the new one containing the address logic and the LEDs.

It's not a very long jump in the development since last time but I just think it's so rewarding to see and hear every new feature and confirm that it's working.
I just had to make a post :)

1 comment:

  1. Thinking about doing something similar, and would like to see some schematics for this!