Hi Mick,
Here's a possible solution, 5 small SCR's, 5 LED's, a TL431 and some
other junk. I offer this only as a "paper" solution because you'll have
to adapt it to your personal preference.
First select the LED's you want to use and choose the current through
the LED. This current should be higher than the holding current of the
SCR. Select this current to be between 10 and 30 mA, I used 15 mA.
( The holding current of a small SCR is about 5 mA.)
Next calculate the common cathode resistor of the SCR's.
3 * Iled * Rk is smaller than 2,5 volts and
2,5 volts is smaller than 4 * Iled * Rk
So select Rk to be about 2,5 volts / 3,5 * Iled
For the SCR's I used BRY55-600 types, it's an obsolete SCR, but a 2N5060
is very similar. It's a small SCR in a TO-92 package.
I used blue LED's with a forward voltage drop of 3 volts at 15 mA and
there was a 0,8 volt voltage drop accross the SCR's.
It's impossible to give you a ready made design because the values of the
series resistors of the LED's and the common cathode resistor will depend
on the type of LED's being used and on the current through these LED's.
on1aag.