Monday, March 22, 2010
Chapter 4 - Exercise 21 - Completed
One thing I'm certainly learning through this process is that no matter how many times you check and double-check your circuit, you've missed something... that is, until it works. The author does a good job of warning us about accidental damage to many components, and my first thought is always "must be a faulty component" - I need to change that to "must be a faulty human."
The good news, for me, however, is two fold - one, my regulator wasn't damaged. But two, the 7432 chip WAS damaged. But the question is whether that damage came about because of my faulty wiring - I'll likely never know, but when I switched out my 7432 (after finding a wiring error - more on that shortly), it started working.
If you look at my picture closely, you'll notice a few differences in the circuit I built and the one on page 210. First, I didn't have a .33 capacitor, so I substituted a 2.2. I tested this before building the circuit and was able to determine that it didn't have any effect on the 5V regulated voltage...
Next, I didn't have two of the 0.01 capacitors so I took a chance and substituted two .047 capacitors for each... I wired them in parallel (opposite of resistors - parallel you add their values) and crossed my fingers that this substitution was okay.
Now - for the faulty wiring. Figure 4-95 on page 210 is fairly easy to follow... but don't make the mistake I did. I had that 10K resistor at the bottom going into the negative column, not the positive. Could that have damaged the 7432 chip? Who knows, but after catching and fixing this error, the circuit didn't work. I went back... carefully checked off each wire in Figure 4-95 and verified I had no shorts and that all wires were done correctly. They were (hopefully).
So next I wondered if it might be a faulty chip - luckily I started with the 7432 instead of the 555 chips... as soon as I replaced the single 7432 with a new one, circuit worked. I pulled it out, put in the old one (same orientation) and the circuit didn't work. Put in the new one... circuit worked. Hmmm... how about that?
I'm including a video below showing the circuit working... I actually soldered wires to my S1 because I couldn't get good connectivity by just twisting the wires into the ends.
So, many lessons learned... again. Check my wiring. It's likely MY fault, not a component. I really am not rushing these builds, but I guess I need to slow down even more... the errors are easily corrected... but also easily avoided if I put a little more effort into slowing down and verifying all my wiring first... I hope my readers are learning from my mistakes and avoiding the frustrations I'm encountering.