Thanks to this fantastic forum (and some good resources on this and other sites), I've been able to use a 74HC595 shift register to drive 8 leds. Now I'd like to replace the leds with small incandescent/filament lamps.(think of these lamps as small light bulbs, I have one that light up when 5v goes through them, although not very bright).
I thought it would be as easy to replace a led with such a lamp, but unfortunately it doesn't work. The lamp doesn't light up (the rest of the leds keep working). :0
Yesterday I also tried the same scenario with a max7219 led driver and got the same result: leds work great, but the lamp not.
Anybody has an idea what's going on? Or anybody has an idea how I can drive a number of these lamps?
Thanks a lot!
Jan
ps if you are wondering why I'd like to do this: I ordered some Numitron IV-9 8 segment filament displays. They haven't arrived so I'm testing my circuit with a small light bulb as a replacement of one filament of the Numitron. (IV-9 data sheet IV-9 - Tiny numitron filament tube)
Well it's all about what the equivalent resistance of the lamp is when powered by 5vdc. So you should measure the current draw of a lamp when powered directly with 5vdc with a current meter and then see what the output current limit is for 74HC595 output pin from it's datasheet. I would suspect that it draws too much current but only a measurement can verify that.
I guess I'll just have to wait a bit for the Numitrons to arrive and replace each led with a filament (each filament/segment uses 17 to 22 mA at 2,8 to 4,5 V so I'll probably have to add a resistor).
I haven't used any of those bulbs myself but the spec seems to suggest wide variability. If so, using a resistor can help even out the brightness of individual segments.