I need a circuit which lights 4 LEDs upon 4 pulses on input. 4017 CMOS counter/decoder seems the obvious choice here, and there are tons of example circuits on the web. However, every circuit I've seen only drives one output at a time (a LED connected to each of the 4017 outputs). What I want to do, though, is keep 'earlier' LEDs lit. So the following would be lit:
count 0 - LED1 count 1 - LED1 + LED2 count 3 - LED1 + LED2 + LED3 count 4 - LED1 + LED2 + LED3 + LED4
I'm thinking I could use diode OR gates (none for LED1, 2 for LED2, 3 for LED3, 4 for LED4 - 9 total), but not sure that this is the right answer. On count 4, 4 LEDS have to be lit - does the 4017 deliver enought current for this?
Do I need to throw a transistor on each output to amplify the current?
Is there a better way?