Ok so you have been out and purchased some 4" (100mm) high COMMON ANODE seven segment leds and you want to connect them to your Arduino. The IC of choice as there has been so much written about it on the Arduino forum and website is the MAX7219 or MAX7221 driver chips, but unfortunately their segment drives will only output 5V DC max and without a lot of extra circuitry difficult to use with these large LEDs as nominally the segments require 9V DC or higher. There is however another ideal chip which is readily available and fits the bill perfectly the WS2803 manufactured by World Semi. Unfortunately they have stopped making the chip in a DIP package and it is only available in surface mount. The PCB I have laid out here uses the latest version of the SM chip which has the original pin out configuration of the discontinued DIP package. The chip has a total of 18 LED outputs ideal for 6 rgb leds, obviously here I have used only 8 outputs connecting to the seven segments and the DP. The anode voltage can be up to 40V DC so no problem driving these large displays. A single Iset resistor R1 on the pcb controls the segment current and for the 9V displays I have used at 20mA per segment R1 needs to be 1K.

This board connects to the Arduino with 5V DC, Gnd, Clkin and SDin it also needs a separate anode supply from an adapter or bench supply to power the anodes. all of this is taken care of on the pcb with power input pads suitable for header pins. The boards are cascadeable with the SDout and CLKout pins of the first board connected to the SDin and CLKin pins of the next and so on. The only other components on the board are 2 decoupling/smoothing capacitors, space provision for a terminating resistor if lots of boards are cascaded and also a resistor in the decimal point line so you can tune the DP brightness to match the other segment brightness as the DP only normally has 2 leds instead of 3 leds in series for the segments. The WS2803 is surface mount so you will need to be able to solder this. Quite easy using a solder paste mask, solder paste and a hot air gun.

The WS2803 works in a different way to the MAX7219 insofar as the output is not multiplexed and all bytes need to be sent, the slight downside is that the current drawn is greater so with 4 boards cascaded you should be able to supply an anode current of around 720mA.

OK what do you get for for your money - 1 - top quality lead free double sided pcb, black solder mask white silkscreen, through hole plated 1 - WS2803 surface mount driver IC. 1 - 1K resistor 1 - 100n polyester capacitor 1 - Electrolytic smoothing capacitor 1 - full set of build and test instructions and a sample sketch to power from an Arduino and bench power supply adapter.

YOU NEED TO PROVIDE THE SEVEN SEGMENT COMMON ANODE DISPLAY.

If this board proves popular I will layout boards for 3" (75mm) and 5" (125mm) seven segment displays and maybe consider a single pcb with 4 displays. Let me know if you are interested.

please feel free to comment or ask questions.