I bought some cheap 8 x 8 led matrices from china and they look good.
I was going to do some scrolling text thing driven by the indicator switches on my bike via an arduino UNO as they are on a mini pcb with a MAX7219 chip, but I have not had any success in getting answers to having the arrows or text scrolling left OR right depending on indicator pressed. So I thought that as they are nice and bright, I could connect a few of them together and use them as a brake light. Just a simple on and off thing. Question is this;
Is it possible to just connect them to my bike power (12 volt) and would I need to add resistors for each matrix, or one for all?
As the title of this post states, and as you probably guessed from the question, I'm very new to this 
It depends on the module.
You will probably have (say for instance) all LEDs in each row anodes connected and all LEds in each column cathodes connected. To address individual LEDs, you would put voltage on the row and ground on the column.
To turn them all on at once you would have all rows connected to voltage and all columns connected to ground.
Whatever happens, you must have current limiting. If you only want individual LEDs or a whole row lit, you would put a R in series with each row and ground the columns individually via another R (for current balancing if more than one LED in the row is on). To turn on all LEDs you would ground all columns via an R in each column.
The value of the R depends on the voltage and the max current allowed in the LED.
Weedpharma
Why not let the Max chips drive the LEDs ?
Powered by a cheap step-down converter and driven by a Mini/Tiny/...
BTW over here (in Germany) it would be illegal to attach such a device to a bike. (30€+)
So are you saying that if I leave the MAX chips on and let them power the matrix I don't need resistors?
AFAIR there is one current limiting resistor per MAX needed, not per LED.
olorin65:
So are you saying that if I leave the MAX chips on and let them power the matrix I don't need resistors?
You require the current-setting resistor for the IC - not directly connected to the matrix.
But to use a MAX7219, you need a microprocessor to initialise it with the appropriate parameters, so it might be just as sensible to complete your original project, using Marco_c's library.
olorin65:
I bought some cheap 8 x 8 led matrices from china and they look good.
I was going to do some scrolling text thing driven by the indicator switches on my bike via an arduino UNO as they are on a mini pcb with a MAX7219 chip, but I have not had any success in getting answers to having the arrows or text scrolling left OR right depending on indicator pressed. So I thought that as they are nice and bright, I could connect a few of them together and use them as a brake light. Just a simple on and off thing. Question is this;
Is it possible to just connect them to my bike power (12 volt) and would I need to add resistors for each matrix, or one for all?
As the title of this post states, and as you probably guessed from the question, I'm very new to this
I bought these.
You need to make certain that the 8x8 LED matrices are row cathode column anode.
One set I bought were; the other wasn't and would not work.
In addition, even if you have the row cathode column anode 8x8 LED matrices, you will need to insert them upside down. Ohm out the PCB and you will see what I mean. Unless your PCB are the more expensive red ones. I haven't tried those.
Thank you all for your time in answering.
I see now that its not just a matter of connecting the live and ground and expecting them to light up.
I will play around with them further and probably stumble on a workaround.
Thanks again