Matching LEDs / battery holder

[Snakey Lane]

Couple of questions from a newbie.

I'm planning to build Nurse Quacky.  The circuit uses two LEDs around the op amps, and the diagram says "the LEDs should be matched".  I'm guessing this means that if I test them with the same resistor, I should be picking a pair that have the same current drain (or as close as).  Is this right?

Second question, are there any neat designs for a holder to hold the PP3 battery inside a typical diecast box?  Or do people just tend to leave the battery loose inside?

Many thanks.

[BAARON]

The current flowing through an LED is determined by the current-limiting resistor they're hooked up to.  What varies, though, is the voltage drop/forward voltage of the diode, which varies from LED to LED.  Generally speaking, if you buy two of the same LED (same size, same colour, same manufacturer, etc), they'll probably be pretty close.  Sometimes you'll find LEDs of different sizes and colours that have the same voltage drop, but it's easier to find pairs if you stay within the same size/colour.  Measure the voltage drop with the diode-testing mode on your multimeter, if you have such a mode.  If not, hook up the LED with a 1k-4.7k resistor in series with it and power it up with a 9v battery, and measure the voltage across the two leads of the LED with your voltage mode on your multimeter to see what it's dropping.

The battery: most people leave it loose, but put it between the footswitch and the bottom of the enclosure so it's trapped and can't move around much.

[Snakey Lane]

Thanks for the quick reply.