Project viability - LED controllers

A

AnWa

New Member
Hi! Newbie here.

I am considering building my own system for controlling lots (hundreds) of LEDs from a PC. I'm thinking of using PICaxes that are addressed through a serial bus. (The bus would need to extend for tens of meters, but one way communication is fine.)

Each point of light needs to be turned on, off or flash (with a certain frequency and duty cycle), but I want the transitions between lit and dark to be smooth, and I would like to do this in software rather than having to solder in extra resistors and capacitors for each LED.

Does this sound like a viable PICaxe project? Are there pitfalls that I should look out for?

Any feedback is welcome.
 
"Hundreds of LEDs" ... are you meaning addressable LED strips? If so, I don't think the PICAXE is what you're looking for. I think there have been some ingenious code bits written to handle comms with the WS2821 (?) LEDs ... But it's very rudimentary ... you're asking for more advanced features ... I think you should be looking at Arduino devices for this particular application.

As for long-range serial comms ... I'd recommend Serial / TTL to 422 converters ... I ran a PICAXE across a pair of these through a CAT5 cable at a distance of about 100 feet ... no problems at all ... was even able to remotely download new code to the PICAXE ... in fact, that's *why* I chose the PICAXE over the Arduino for that particular application; the TTL/422 converts don't pass the reset signal needed to initiate an Arduino download, but they DO pass the BREAK signal needed to initiate a PICAXE download.

Horses for courses.
 
That you.

No, it's for discrete LEDs. Each PICaxe would only control a small number of them (maybe 4 - 8). If any of them need to flash, they would flash in unison, so I think one thread/process would be enough to handle the LEDs while a second one handles the serial interface and hand over incoming commands to the LED driver.
 
Well, it's *doable* ... but not easy. Start with 2 PICAXE and 8 LED each ... you'll have to work up your serial protocol to address them individually, and then a protocol for LED command/control.
 
Thank you!

(And the "That you" in my previous post should also have been a "Thank you". English is not my first language, and the computers' auto-correct function does strange things when I type in different languages.)
 
By sending and ID and a single number via the serial link. Use this number to select a subroutine For the LED pattern you require. Also use PWM control for the LEDs to change the brightness for a soft start effect OR slow OFF effect. A second byte can be added to change pulse rate etc.

Bill
 
Bill.b said:
By sending and ID and a single number via the serial link. Use this number to select a subroutine For the LED pattern you require. Also use PWM control for the LEDs to change the brightness for a soft start effect OR slow OFF effect. A second byte can be added to change pulse rate etc.

Bill
Click to expand...
Yes. That sort of communication is what I had in mind.
 
I wonder if I could use I2C or RS-485. I'm not sure about their maximum distances. Maybe one could use repeaters?
 
AnWa said:
I wonder if I could use I2C or RS-485. I'm not sure about their maximum distances. Maybe one could use repeaters?
Click to expand...
Standard i2c limit of reliability at 100kbits/sec is 1.2 metres. With an i2c extender chip at every drop point, the bus can be extended to a little over 12 metres, once again at 100kbits/sec. Line capacitance is the limiting factor so, if you lower the bit rate, you can reach further. However, i2c is unbalanced and is very susceptable to noise as transmission lines get longer.

I would suggest you use RS-485 but you have to write an extra layer of message handling for it. (In a PICAXE the i2c firmware does the message handling for you.)
 
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