Possible To Use Sub Shift Registers?

Hello Community, I was wondering if it's possible to run sub shift registers off another shift register? maybe using ShiftPWM I don't know. If it's possible but I'm only new to this kind of stuff so I'm not too sure if there is a way.

Sub shift registers?

If you mean daisy chain, then yes... basically the serial data fed in gets spit out to the second register and repeat for a 3rd register.

No I mean like attach several (sub) shift registers to the output pins of the first (primary) shift register.

Yes. of course it is possible but the question as always is- why?

What is it you hope to achieve? Cascading in this alternate fashion will not allow you to shift data any faster - nor will it be particularly slower. It will rearrange the data into a sort of "waterfall" as it is shifted or "raster" as it is finally latched. And you are actually wasting the first shift register as its outputs go to feed the others instead of being part of the final output.

Some of us are wondering what your secret (undisclosed) plan actually is. If for example, it is to light LEDs, then it is an inefficient and expensive way of doing it. Whether you choose the inexpensive eBay ones or the "full-price" version of each device, it is actually more economical in all ways to use MAX7219s (or actually, the HT1632) to drive LED arrays, even for RGB LEDs as you have previously mentioned - and there may be better options again.

since one bit get's shifted in & out bit by bit using the same clock....

Simply connect the first pin of the sub register along with the shared clock, it will processed on every bit in... or parrereled in with 8 bits... so question is which shift registers?

I just thought about this and it doesn't sound like a good idea. What I'm trying to do is light a lot, and I mean a lot of RGB LED using ShiftPWM but I checked the interrupt load on the calculator on the website and it is in the red. So what would this actually mean?

Don't know if it will make this any easier to work with but I'm going to be using 380 RGB LEDs so I should be needing to use around 150.

If there is any other way of going about doing this please let me know.

Also the Arduino I'm using is the UNO (The one I'm using is made by Freetronics) so would it be worth buy the EtherMega by Freetronics?

Same 8-bit processor core in all of them, so interrupt handling will not improve. Have you considered chips like WS2811, WS2812? Some have controller integrated with an RGB LED, supply power & gnd to all, pass along serial data to light up as needed. http://www.adafruit.com/products/1138 http://www.adafruit.com/products/1558

Well which one of those would you say is better to use because I'm going to be making big letters and won't be needing like a whole DMD because I'll only be using like a border and a few internet LEDs to construct a letter. If that makes sense.

joshl_1995: If there is any other way of going about doing this please let me know.

As I said - use MAX7219s. IF you are using common cathode RGBs, each will drive 16 RGB LEDs, so that would be 24 chips, only 24 resistors and 48 bypass capacitors. You only use six of the eight anode drives per chip so you sacrifice a quarter of the functionality of driving individual LEDs, but that is still a minor loss.

You can use common anode LEDs - exactly the same numbers but the programming logic is (I think) a bit more obscure. And other chips such as the HT1632 are even more economical.

I'm looking at maybe using these http://www.adafruit.com/products/1138 as CrossRoads was saying. However just want to make sure if they can be cut into smaller strips? then just angle them and rewire them.

"The strip is made of flexible PCB material, and comes with a weatherproof sheathing. You can cut this stuff pretty easily with wire cutters, there are cut-lines every 0.65"/1.7cm (1 LED each). Solder to the 0.1" copper pads and you're good to go."

Ok good so would you say this would be easier to use due the amount of LED's I'll be using? so seen for this it says "The PWM is built into each LED-chip" does that mean I won't have to worry about what pins I hook these strips up to?

The software that drives the LEDs is written for a couple specific pins. Do some reading a the adafruit website.

Ok will do, also would you say it's worth upgrading my Arduino Uno (Eleven by Freetronics) to the EtherMega also by Freetronics?

Upgrade for what? Are you running out of IO? Flash? SRAM?

I don't know, I just though maybe I would have to as I thinking about having a about 5 buttons as well as the many LED strips. Also I don't know if the Arduino I got could handle it. I don't know much about them, so if it's not worth it or needed I won't worry about it then.

An Uno can do quite a bit. The IO you describe does not sound like you will need more pins. The light patterns can be stored in Flash memory as it doesn't sound like it will need to change on the fly - so you could have like 3000 bytes, with each 3 bytes storing 1 of 256 levels for an RGB LED, and still not be pushing the limits of what a '328P chip can handle.

Ok, that's good to know. Thanks for the help.