After I took a visit at Talking electronics Interactive at
http://www.talkingelectronics.com, I found that they have many useful circuits, one of them which could suit your requirements very well.
Here's an experiment.
There is this black chip with the number "555" printed on it. It has 8 pins. A 1/2 circle is carved out of one end of it, or a carved in dot is created in it. Align the chip so that the marking you see is on the left. The pins are numbered 1 through 8 starting from the bottom left going to the bottom right, then from the top right to the top left. This chip is a "timer".
Now you will need two resistors. These are mini peanut-shaped items with stripes on them and metal wire coming out of their ends. This metal wire is more known as leads (not pencil lead). Look for the following stripe colours in order: brown, black, yellow, gold. you might have to move the resistor around to see it. This resistor has a value of 100 kiloohms.
Also, get a hold of a resistor that has these color of bands on it: orange, orange, black, gold. This resistor has a value of 330 ohms.
You will need an electrolytic capacitor. These are barrels with markings on them, and they have two leads as well.
You will also need wire, and a breadboard (an item that has many holes in it.
Plug the chip into the center of the breadboard. make sure that when the chip is seated into the sockets, you can read the 555 properly, not backwards.
In the following, when I say connect, it means insert the device in the same column the pin is in. It doesn't have to be in the same socket, as there are 4 other sockets to play with.
Connect pin 1 (of the chip) to the -ve (bigger round connector) of a 9 volt square battery. You will need a wire to do this.
Use a piece of wire to connect pin 2 to pin 6.
Connect the capacitor to pins 1 and 2. The leads of the capacitor cannot touch each other.
Connect the 100 kiloohm resistor to pins 6 and 7.
Connect the other 100 kiloohm resistor to pins 7 and 8.
Connect pin 8 to +ve.
Connect pin 3 to one lead of the 330 ohm resistor.
The other lead goes to the anode of an LED.
The cathode of the LED goes to the -ve of the battery.
The LED is a light-emitting diode, or in simple terms, a light bulb with better efficiency. The anode is the "positive" part of the LED, and the cathode is the "negative" part. When looking at a new LED, you see two plates of different sizes inside. The larger plate is connected to the cathode lead, and the smaller plate is connected to the anode lead.
You should see the light go on and off at a constant rate.
I might have gave too much for an answer, but Talking Electronics Interactive will be able to provide much more information for free.
They will have circuit diagrams, one of them which described my circuit, but instead used different values.
Basically, I showed you how to make what you need. As for the same casing, good luck.