23=A resistor to limit current flow for all the LED's
(how do a select the correct vaule?)
From a datasheet:
Table 10. Output current-R-EXT resistor
R-EXT ([ch937]) = Output current (mA)
7370 3
4270 5
2056 10
1006 20
382 50
251 80
200 100
You could even use an adjustable pot to set the final value to your liking after you have it running.
Lefty