Actually there is no any row drivers (can you believe it?) Only the column drivers using ULN2803A.ULNs driving through Jonson counters.I did not use shift registers because I have plenty Jonson counters at home.
The secret is in the software & in that special LED.
Actually there is no any row drivers (can you believe it?) Only the column drivers using ULN2803A.ULNs driving through Jonson counters.I did not use shift registers because I have plenty Jonson counters at home.
The secret is in the software & in that special LED.
I'm confused. I assumed you were driving rows with the 74HC4017's but now I realize there's no practical way to provide 30 bits of data onto the four ULN2803 inputs. How are you scanning this matrix? Schematic?
I'm confused. I assumed you were driving rows with the 74HC4017's but now I realize there's no practical way to provide 30 bits of data onto the four ULN2803 inputs. How are you scanning this matrix? Schematic?
Ok, ok. I understand. I'm very "dense" today (grin).
Thank you for the explanation and for being so patient.
Again, very nice design! It uses many ICs but they are very inexpensive ICs so that is a good trade off. And you seem to be getting very good brightness for only 1/30th duty cycle.
I would prefer to "scan" the rows to increase duty cycle and reduce "peak" current requirements for full brightness.
You could easily modify and expand your 7x30 circuit using this method;
(1) remove the current limiting resistors from the row pins.
(2) install row driver transistors. you'll only be driving one row at a time.
(3) use 74HC164 or 74HC595 or similar 8 bit shift registers for the columns.
(4) drive the ULN2803 sinking drivers from the shift register outputs.
(5) install current limiting resistors on the ULN2803 outputs.
Actually, you'll probably want to use row driver transistors for every 10 or so columns unless you install some very "big" transistors (grin).
I would actually use 8 bit serial-to-parallel sinking driver ICs for the columns instead of the dual IC combo' but they're expensive. For the dual IC combo' I guess I would choose the 74HC595 over the 74HC164 because the '595 has a latch which would allow us to take our time loading 100 bits of data into the shift registers without messing up the display. The '595 also has an output enable pin which could be driven by a PWM signal to control display brightness.
With the very good brightness you're getting on your 7x30 display with only a 1/30th duty cycle, I am thinking that you might actually have several different options for an expanded 7x100 version. Perhaps you don't really need to use 13 74HC595's and 13 ULN2803's for a 1/7th duty cycle 7x100 display.