Chapter 4! Finally getting into integrated circuits which have always interested me but I've never quite found a good explanation for how to use them or how they work... until now. That said, I did have to read over this first material about 3 times before it really sunk in. But it's now "sunk."
This exercise is all about the 555 Timer chip. My initial thoughts before reading this chapter was that this was a timer that would keep time... right? Like a stopwatch. Wrong... sort of. I guess it can be used that way in certain circuits, but it's really about holding a pulse (current, I think) for a certain amount of time... an interval that we have control of, by the way. By changing the values of different components, we can manipulate a pulse emitted (allowed?) by the chip to last a specified time (with slight variations).
My photos here show the circuit I built using the schematic on page 155 (Figure 4-15). I tried my hand at building the circuit by only reading the circuit and not looking at Figure 4-16 for help. I got it right the very first time... I was happy about that.
A few differences, though - I lacked a 100 microfarad (C3) capacitor so I substituted a 220 microfarad... since this is for voltage smoothing, I was guessing that as long as it was a minimum of 100mf that I'd be okay... wasn't 100% certain, but willing to experiment. The rest of the components I had in my kit... be sure to note that the voltage has been switched on the breadboard to 9V and the sides are changed - positive voltage on right side, negative voltage on left side. I also had to go back and refresh my memory about the symbol for an LED because I couldn't remember if the long wire was where the arrow was pointing to or away from ("away" is the answer).
Also, be VERY careful with the orientation of your electrolytic capacitors and make certain their positive and negative terminals are inserted into the breadboard properly. Luckily I checked over my components before applying power and discovered I'd reversed C4. I also soldered two lead wires to my potentiometer to make it easier to insert into the breadboard and avoid using patch wires.
Below are three videos - for the one with R4 equal to 100K, the LED stays lit for about 5-6 seconds... difficult to measure it accurately at this point. I next more than doubled R4 to 220K and, as expected, the LED stays lit for well over 10 seconds. Finally, I cut R4 in half and substituted a 51K resistor and the LED stays lit for around 3 seconds. I wanted to mess around with different capacitor values, but my capacitor selection is limited and they are also not as easily doubled and halved in values like resistors.
It does bring up a question which I don't think I've seen covered in the book yet - can you add capacitors like resistors? If I add two 47mf capacitors in series, will it behave as a 94mf capacitor (close to 100mf)? I may play around with this but am not certain if I'll be risking my components... just not sure if this is safe or not. And I don't have enough capacitors to play around with right now, so I'll likely pick up a mixed bag some time this weekend.
I enjoyed this chapter - I'll likely go back and read over this material one more time before starting Exercise 17... not all the pins on the 555 chip have been covered in detail so I'm still fuzzy on some of their uses, but I definitely understand how pins 2, 3, and 4 work and I'm getting better at pins 6 and 7...