TheMilkGuy
wibbled on Tuesday 06 April 2010 14:03

Thanks for the reply Tim,

I live in Canada, but I'll have a look into Maplin.

I think I'll try to keep things analogue - my knowledge level is so
low I'll spend my morning googling most of the phrases you used! haha

Ok.

In that case, the classic way to start would be 10 leds and a CD4017 counter
(or one of the many modern pin-equivalents with "4017" in the name) + 555.

The 4017 takes a clock in from the 555 and sequentially fires one (and only
one at a time) of 10 outputs.

16 could be done with a binary counter and 4 to 16 binary decoder.

The 4017 will drive an LED directly at modest currents.

The LED circuit might look like:

C1
---------- |----------| |------------------|
DRV--| R1 |--| |
---------- | --------- |
--------| R2 |------||--------
--------- LED


R1 is to limit the inrush current to C1 (to protect the chip driving DRV)
R2+R1 should be so that the LED draws about 5mA (assume the LED drops 2V,
then apply Ohms law to the difference between your supply voltages minus 2V
at 5mA.

R2 several times (3-5) times the value of R1 (guesstimate, experimentation
needed)

C1 - try anything from 10-470uF until it looks right. There are ways to
calculate this, but it's probably better for you just to play.

Choose a mega bright LEDs (more light for your 5mA). Old fashioned
"standard" ones will be a bit lame driven like this.

Expect to burn out one of your driver chips (the 4017) Buy 2 or 3.

Have fun

BTW, the "old" CMOS CD4017 will work at all sorts of supply voltages (4 or
5-15V IIRC). Many of the new fancy types are aimed at TTL 5V or 3.3V
"modern" logic standards, which makes them fussier to supply. For fiddling,
I always preferred the old CMOS CD40xx series as anything from 6V battery
pack, 9V PP3 or 12V wall wart would suffice to power them. But watch out for
static electricity - you can fry them just by touching them. The old simple
trick is a bit of wire, bared and wrapped around your wrist, or tucked under
a watch strap. The other end is clipped to a radiator pipe or other earthy
bit of metal (do NOT wire to a mains plug, even the earth pin, - proper
earth anti-static plugs have resistors in them for safety. A wire in a plug
has too many ways to go wrong and zap you in lethal ways.

--
Tim Watts

Managers, politicians and environmentalists: Nature's carbon buffer.