Arduino VFD Weekend Project

[klightspeed]

The arduino pins should be able to sink enough current to drive the cathodes of the LED displays - you might want to use 1 port (8 pins) to drive the cathodes, with 1 resistor on each of those pins, and 7 pins of another port (4 enables + 3 disables) to drive transistors that drive the anodes, something like the following for the anodes:


Be aware that the more you try to multiplex it, the dimmer the digits will be.
Trying to use 4 sinks + 2 enables for the cathodes, and 3 sinks + 4 enables for the anodes will give each segment a maximum duty cycle of 1/24, which will result in a brightness of 1/24 full brightness, and 1/6 design brightness.

[CirCit]

im not sure I can use the analog pins so I think 8+7 is 1 pin over budget

http://www.arduino.cc/en/Reference/PortManipulation

if I can use the analog pins then id make port D map straight to the segments
and then use standard digital pin calls to the remaining 12 pins and I should need 0 transistors and 7 resistors (or 12 if its better the other side)

the flow then would be
set port d low
set all other pins high (or reverse these 2 for com anode / cathode)

set a digit pin low
do 1 port command to write the whole segment in 1 go
wait abit
set port d low
increment digit and loop

[klightspeed]

Originally Posted by CirCit

im not sure I can use the analog pins so I think 8+7 is 1 pin over budget

The analog pins of the Arduino are on PC0..PC5, RxD,TxD are on PD0,PD1, the crystal is on PB6,PB7, and the in-circuit programming header is on PB3..PB5. If you don't use the ADC, you can use Port C as digital pins. Even if you do use the ADC, any pins you don't use as analog inputs are available as digital I/O. I think the programming header would just be for rescuing the arduino if the bootloader becomes corrupted, so you'd have a budget of 6 pins on each port, or 18 pins in total.

You could combine 8 pins from two ports to control the cathodes, and combine 7 pins from two ports to control the anodes. e.g. PC0..PC5,PD6,PD7 for the cathodes, PB0..PB2 for /SELA../SELC, and PD2..PD5 for SEL1..SEL4

I'm not sure you can get away without using transistors for the anodes, as displaying "8." with a current of 20mA through each LED gives a total common-anode current of 160mA. This is well beyond the limits of the Arduino - each digital I/O pin is rated for an absolute maximum current of 40mA. Having the Arduino drive the anodes, and using the cathodes as segment selects would exceed the absolute maximum aggregate current handling capacity of the Arduino - this limit is 200mA, and 12 x 20mA = 240mA.