>> 11a. "you don't know how cheap the
>> lowest end microcontrollers are. "
> You've got that right. And I'm willing
> to learn. The stuff [I've seen] at Radio
> Shack is about seventy to a hundred
> dollars. Can you point me to something
> as cheap as two relays perhaps?
OK. Forget the RS stuff. They are Parallax (Basic Stamp) stuff. I think they are actually EXCELLENT kit for learning. They give away hundreds of educational PDF online for free. The best thing about them is that you follow the document and everything works the first time. We get people here from time to time asking "why Pic program don't work even though I copied everthing exactly".
Having said that, technology have moved on, and Basic Stamps are way too expensive for one-off projects. I'm thinking PIXAXE for you (also programmed using simple BASIC language). A single PICAXE can be had for about 2 British Pounds (I think that's about $3 or $4 dollars). But you probably do better to a starter kit with programming cable, etc. Google Picaxe - and look for US distributor (or whatever country you might live in).
Then you can program the uC to count till about 30 minutes, then either bring a line low (0V) or high (5V) and drive a transistor or small relay. From there it is matter of driving a bigger relay or a solenoid directly.
On the uC, just about the only thin you need is (a) battery (b) switch to turn the thing on (c) V regulator. Much simpler than using 555 with also requires battery + switch + regulator AND few other resistors and capacitors.
Having written all this, I just realized about 10 years ago, I bought a garden timer. It basically works like an automatic light timer - except it is weather proof. I would think this device turning on and off a 120v (that can drive a solenoid) is the simplest answer to your problem.
I think hardware store have them for outdoor lights, etc.
>> 15. " I would think ... a 555 timer IC
>> ... would be the cheapest and easiest."
> Sounds right. However, and please put me
> right (send me a schematic) if I am wrong,
> but I thought I read that the 555 couldn't
> be employed for seriously long (30 Minute)
> time delays.
Actually there are few ways to implement this solution using 555. The simplest way is to let 555 wait and wait and then send out a signal to open a latch. This is kind of hit or miss (long delay). Another way is to let 555 create up and down signal (an oscillator) and feed that to some sort of counter. When certain amount of up / down signal is counted, it can flip a switch. I would personally think this is more dependable (but more complex too).
In essence that is exactly what happens INSIDE a microcontroller with proper software / code. But the hardware is all in one chip.
> The EASY part is (for me) the mechanics
> which, if I can find a way to pull the
> solenoid open electronically, is a done deal.
Good. Tell us which ave you want to try (uC or discrete components).
> Still need a long-term (30Min) timing
> circuit diagram or two - please.
Again, do you still want to go the old electronic (analog) using some sort of 555 or go digital with microcontroller?
P.S. I still think you should experiment with uC (in the long run). Once you realize how easy things are using a uC, you just might go nuts making all sort of new gadgets around the house.