Help on I2C question

Clem,

          Not I2C but SPI.  Have a look at Majenko.co.uk  he does a 32 port IO expander board and up to 4 can be used on 4 wires from the Arduino i.e. 128 IO!   I use these to drive banks of 8 relays via opto couplers, these come as ready made boards.  The realys can switch any voltage you like.

The Majenko stuff is very good quality and he produces a library to drive the boards.

Bob

does it have to be i2c because there is a lot of ways to address 50 transistors switching 12v+ but if you have to use i2c maybe a port expander with transistors connected could work something like Expanding the number of I/O lines using Microchip MCP23008 | Embedded Lab it would help if you could say more about the project.

@bobcroft

     I could use SPI interface from what you show. Researching that angle. Would like something elegant/simple to do...

@Michael Oldfield

     Need to check this one out too because transistors should be rather inexpensive. MCP23008 could be the key to switching these. About how fast do you think this can occur (the switching).

Thanks to all,

Clem

The MCP23008 according to the datasheet MCP23008 - Interface- Serial Peripherals can switch at 100kHz, 400kHz and 1.7MHz I²C with the transistors depends on which ones you use but normally very fast and to save on pins you could do a 7x7 matrix and it should only use 8 pins i think if you have a common ground but that would only be 49 transistors. if you where going to use SPI the 595 series shift register at 20mhz could be a cheap option http://www.nxp.com/documents/data_sheet/74HC_HCT595.pdf but can use a lot of memory and you would still need transistors but like i say it is hard to offer solutions without knowing more like how many amps at 12v, what type of load the more info the better.

Looking at 300 LED's at 20 mA each for a total around 6 A if all on with white! Really hope not to do this... I plan on feeding this with old 120V-> 20 volt/6 A laptop regulator rated at 90 watt's into a buck DC to DC down to 12 Volts. Am I crazy? LOL

Oh I plan on dividing these into groups of 3-6 LED's per cup...

If you have all that stuff already then no, not crazy at all

I would do the same

Peter

i can help with what your planning i had a feeling it was going to be leds and i had to do something similar in a limousine. Their is some great IC`s out their for just this kind of thing but if you are a masochist take a look at http://en.wikipedia.org/wiki/Charlieplexing i dont have much time at the moment but i will help more tomorrow and try and put all i know about controlling large arrays of leds but if they are RGB leds then you will need to triple the current because it is 20ma per colour so 60ma with all three colours on to produce white but if they are being PWM`ed then it is unlikely that you will every reach the full 18A also if you connect some in series you can lower the current but will need to raise the voltage.

PS its not crazy sometimes you just have to climb the mountain because it is there

Hi sorry for being so late but here we go if you have not purchased anything yet then maybe look at something like NeoPixels : Adafruit Industries, Unique & fun DIY electronics and kits they are more expensive than normal led strips but much easier to control and if you look on ebay for addressable leds you will find cheaper alternatives but if you already have 12v strips you can lower the voltage by removing the resistors on the strips which will bring the voltage down to about 6v per color line but it is a lot of work. if you need to have a scale of color and you need to change it fast the TLC59 series IC`s are a better choice than 595 shift registers from Texas instruments LED Driver ICs | Products for LED Drivers | Power Management | TI.com and you will get 8bit grey scale control of each colour which is 256 shades of each colour to mix with both through hole DIP and surface mount IC`s but what every you do I think you are going to need to use transistors.

Logic level transistors would be best due to the lower gate voltage something like the IRLZ44N but depending on whether the strips are common anode or common cathode you with have to use NPN/N-channel or PNP/P-channel transistors or Mosfets but you could use non logic level transistors by using 2 transistors like the BC337 from the mircocontroller to the Mosfet to enable you to turn them on fully and lower the heat dissipation by the transistors. one last thing remember to add pull up or down resistors on the mosfet get pins.

There is some good info out their on controlling led walls with teensy like these 800+ LED Wall With Diffuser Panel is a Work of Art | Hackaday  https://www.youtube.com/watch?v=ufqte-Je7Zo there is also a tone of good led control libs for the arduino https://www.google.co.uk/search?q=arduino+library+led+&oq=arduino+library+led+&gs_l=serp.3..0j0i22i30l3.35273.35772.0.39… i hope some of that ramble helps Mick

Hi Clem!

Is this related to the Xmas lights challenge? Could you sketch roughly what you wanted to do with the I2C control and LEDs, I wasn't sure what the I2C control was for (i.e. is it to switch different banks of LEDs into the Arduino shield)?

Also, I2C isn't good for long distances often (but maybe your requirement is for short distance) and a serial chain of 50 would have an impact too (there are workarounds, e.g. additional repeater type chips, or use additional I2C bus,etc).