Driver chips for numitrons

Using Arduino LEDs and Multiplexing
1

Hello,

I need to drive 9 seven-segments displays (which are numitron tubes, actually). The typical supply voltage is 4.5V and each segment needs about 20mA. I plan to multiplex them to save microcontroller outputs. But I'm having a hard time finding the right IC given the sheer number of varieties available on Farnell/Mouser (I'm not even sure in which category to look :~).

I need ordinary 3-inputs, 8-output logic chips with the right current/voltage requirements (nothing fancy). I also need general-purpose transistors to use as switches (to cycle between the anodes). Could you direct me to models suitable for my project ?

Thank you.

2

tlc5916 may work:
http://forum.arduino.cc/index.php?topic=65492.0

3

If I understand correctly, this one works with a serial input. This means I'll need several serial pins if I want to lit more than one tube at a time (and with 9 tubes, this could produce a lot of flicker). I'm rather looking for a chip like the SN7414 (used for Nixies), with logic inputs, but for seven-segments display.

4

but for seven-segments display.

So that will be the 7449 or 74LS49 or 74HC49 then

5

Thanks ! Altough I couldn't find these specifically, this one (74LS47) looks like a close sibling.

I went through the datasheet and there are some elements I am unfamiliar with:

  • Off-state output voltage : 15 V
  • On-state output current : 24 ma (more specifically, is this "per segment" or total ? because each segment consumes 20ma)
  • High-level output current : -50 µA
  • Low-level output current : 3.2 mA

What does these mean ? (forgive my newbiness)

And for my anode transistors, is the 2N2222 what I'm looking for ?

6

Yes it is quite a confusing data sheet with what apperes to be the same page repeated multiple times.

Off-state output voltage : 15 V

The voltage that can be on the open collector output transistor in the chip. In other words you can pull up to 15V.

On-state output current :

The current you can pull through any one open collector output when it is on. Note this is given as 40mA.

High-level output current : -50 µA

Only applies to variants that do not have an open collector output but the internal 2K pull up resistor.

And for my anode transistors, is the 2N2222 what I'm looking for ?

Yes that will do.

7

Many thanks.