Step 2: The circuit
on the arduino, the frequency pot goes to A0, the tempo pot goes to A1, the record button goes to pin 9, the tempo LED goes to pin 10 and the speaker goes to pin 11.
On the ATtiny 45, you will have to choose what pins everything will go to since the sketch is setup for the arduino and you will need to change the pins. be sure to put the speaker and button on either pins 0 or 1 (5 or 6 on the chip).
If you use the arduino to do this, there are a ton of unused pins and plenty of space in the code for you to add your own personalized affects. Maybe add a glide button, or maybe even an LFO pot. There are practically no limits. Even with the ATtiny45 you could replace the tempo LED with a button/pot and add some extra affects.