This post is for Step 4 (of 4) for Exercise 11.
The goal with this final step is to take what we've learned about the transistors and PUTs and use them to create an oscillating sound similar to a siren. We've already built 95% of the circuit, and the new circuit (on page 91, Figure 2-113) requires removing the LED and adding in a resistor (R10) and a capacitor.
I lacked another 2.2 microfarad capacitor (I used my only one for C1) so I found two possible replacements - a 0.1 microfarad and a 4.7 microfarad. One is less than the required 2.2 and one is more... so my guess was that if the 2.2 microfarad was going to cause a wah-wah-wah alarm sound, that one of the substitutes would likely cause the alarm to sound faster... but which one? Best guess was that it would be the 0.1. Why? Well, one of the tasks in Step 4 was to insert ONLY the R10 resistor... no capacitor. I did this (but forgot to shoot video) and the sound it made was super-fast wup-wup-wup sound... (sorry for getting super technical again in my descriptions - these things cannot be helped).
the 0.1 microfarad cannot hold as large a charge, so it's obviously going to discharge but faster... that was my thinking. The first video will let you see the sound I heard when I plugged it in.
Next, I pulled out the 0.1 and put in the 4.7 microfarad capacitor. The second video will let you see the results of that circuit.
All in all... a very fun exercise. Tomorrow I'm going to do a few of the tweaks on page 92... so I won't be taking this circuit apart just yet... I'll try and make some guesses for what's going to happen when I sub in various parts, but I hope I'm wrong... because it'll make me examine the circuit and figure out why I was wrong. I learn better that way...