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500-in-1 Electronics Kits?
Oneamp asks: "I'm interested in a '500-in-one' type electronics kit. Amazon lists a few, but I've seen some user reviews that maybe they are not all they're cracked up to be. Most of the complaints seem to be of the 'Manual sucks' variety. Nevertheless, I'm sold on the idea. Can any of you, who have had actual experience with any of these kits, recommend a good one?"
To be honest, I think your best bet is to get the kit and the "manual" separately.
A few years ago I had the opportunity to tutor an absolutely prodigal young kid, who happened to be 'into' electricity that season. I couldn't find any electricial kits that seemed up to snuff in both the hardware and manuals departments, so instead I ended up taking one of the bigger Radioshack kits, and then using some of the Forrest M. Mims III books as project guides. Why they don't have that guy do the manuals for the kits I have no idea, because he's really quite good.
For the few projects we wanted to do where the board didn't have the right parts, I just hacked them on, either in place of parts that I thought were trivial (resistors, etc.), or just by drilling a new hole in the board surface and adding it in.
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When I was younger I had this 200-in-1 kit which I am amazed to see is still being made! The manual for this one was good, at least in the edition I had. It included circuit diagrams for everything along with some explanation. Early circuits included wiring instructions - later on, you were supposed to figure those out from the circuit diagram. The projects start simple: by the end, you're using almost all the components on the board.
I see that the same company makes a 500-in-1 kit. Assuming this is of the same quality, it would be worth considering.
The problem with the 200-in-1 kit is probably common to all such kits. The transistors, ICs and LEDs are real - they are easy to damage by incorrect connection. You can replace the transistors with a bit of effort, but some components are soldered directly to a board. It's a real pain if you damage anything. I also don't like the use of batteries as a power source. I suppose that's a safety thing, but I'd prefer a good quality low-voltage PSU with an electronic fuse.
I think the next step after a kit like this is making your own circuits from 74-series logic ICs, which provide basic logic functions and some more complex devices like flip-flops, registers and counters. You can make all sorts of fun stuff with this, and you really only need a data book that covers the 74 series, a breadboard and a 5 volt PSU. This is great fun. Especially when you add a microcontroller!
>north
You're an immobile computer, remember?
An op-amp is basically two transistors with the emitters joined together and connected to ground through a large resistance (ideally, a constant-current sink; but bear with me for now). The collectors are connected to supply via load resistors, and one of them is labelled as the output. (The other collector can be used as an inverted output, for connection of another stage to give more gain.) The two bases, with series resistors, are the inputs; the non-inverting input is the base of the transistor not serving the output.
When a voltage is presented at the inverting input, a current flows into it; the transistor on that side tries to let a larger current through its collector (and thus its emitter). The voltage at its emitter -- the output -- goes down. When a voltage is presented at the non-inverting input, a current flows into the base of the transistor on that side and it tries to let a larger current through. But the shared emitter resistor means that the other transistor can't let so much current through anymore, so the voltage at its collector goes up.
The reason for using a constant-current sink in the emitter path is that the changing collector-emitter resistances of the transistors can be significant, making the transfer function horribly non-linear unless the device is only working over a very narrow voltage range (much less than the supply voltage). This was never a problem with valves, when the circuit was called a "long-tailed pair" in reference to the large resistance between the two common cathodes and ground. Fortunately, constant-current sources and sinks are not hard to build using transistors, as long as you can find a pair which have similar electrical properties (obviously) and are in good thermal contact (so temperature variations affect both equally). Such conditions are easily met in an IC.