Hi, my name is Dan and I'm working on an LED retrofit for a '73 cougar (that one with the sequencing taillights).

I created alternating red and green sections of LEDs to light up, the green being just for shows and the red which will be for braking/stopping/sequencing turns.

All told, there are 20 channels per side with 40 altogether.

This is a problem since my basic stamp only has a maximum of 16 I/O pins, and after feeding it a marker, brake, left and right signal line that's reduced down to 12 pins.

Is there any way I can talk to all 40 channels or even just 20 of them utilizing the 12 pins I have left free?

I COULD use four 4017's and trigger them seperately, which I probably will do in the short term... but I'd like to have a microcontroller so I can utilize all kinds of special effects with a click or two of a button.

If there are any recomendations, including perhaps moving to a PIC I'd appreciate the help.

Thank you

 

As for larger PIC, you can use a 44-pin version like the 16F914/17. This will not get you 40 pins of I/O's yet is easy to multiplex into banks using transistors or drivers. 2 to 3 transistors and a 44-pin PIC would work just fine.

Alternatively, the imployement of serial to parallel shift registers will also suffice. Texas Instruments is one of the top sources for serial to parallel shift registers.

Reference to my 44-pin PIC 72-led controller.
http://www.electro-tech-online.com/m...ight=sequencer

 

You need to look up 'multiplexing' - try my tutorials for a start - your 12 pins can drive 36 LED's easily (6x6).

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

What is a "channel"? Is it a group of LEDs or a single LED?

Actually, it probably doesn't matter. You probably need drivers anyway, so......... how about a 3 pin interface and 40 channels of 500 ma "sinking" drivers (no multiplexing required)?

Attached Images

40channels.PNG (11.9 KB, 12 views)

 

I like Mike's option the best... do these chips use I2c signaling?

Nevermind...looking at the datasheet they're simply serial in parallel out shift registers it seems :-P

So i'd just give them a clock rate and on every edge of the clock signal it would advance what was at serial1 over to the next output?

Oh, and I'm driving the 40 channels through the sharp PQ0X series of regulators, they're really wonderful-they have a 2 amp limit, output a selection of voltages between 3.3 and something like 24 (I use 5 and 9 in my project) and they have an on and off terminal-the best feature I think. show it a high or no connection and it turns on, show it a low and it shuts off

 

I think you've got the idea. The clock pulse shifts another data bit into the 40 bit shift register chain. Pulsing the strobe pin transfers the 40 bits of data in the shift registers onto the driver outputs.

DigiKey sells the Micrel MIC5821's. Or, you might sample the Allegro A6821's.

Have fun. Mike