Hello everyone,

I am a newb to circuits. I am building a compressed water rocket and want a simple apogee detector that can deploy a parachute. I decided to use a mercury switch to trigger a servo to go from 0-180 degrees and release a rubber band. Simple, right?

I found a bunch of circuits to do this and no two are wired the same (?). That, and they don't seem to necessarily work.

So my newb questions are these.
1) Is this normal?
2) It seems that there are many ways to skin this cat. I see posts from experienced members referencing a circuit and they say "that'll never work" although others have built the circuit and it worked for them.
3) Notation. Ex: Diagrams reference nanofarads frequently, and yet retailers often reference microfarads only and then want to ignore a leading decimal character when searching, for example. Is this an attempt to torture us newbs?

Anyway, I built a circuit based up this one:

http://www.hvlabs.com/555servo.html

Which appears to be based upon this one:

http://www.sentex.ca/~mec1995/gadgets/servo3.htm

I chose these because they appeared to be the simplest. Was this a mistake?

It was stated by a member here that 68k ohms was way too high for both these circuits. Why would Tony van Roon do that, then?

Does any one have a step by step for one of these circuits? If I make a video of me building it step by step on my breadboard would that be worth doing? I'm willing to do it in hopes somebody would be able to quickly say "In step 7 you have the diode backwards" for example. Or would that be a waste of time? I really don't want to spend a lot of time collecting resistors and capacitors to try every circuit out there. I also don't want to spend a ton of time getting my own version of an EE degree just to build a basic servo controller (which is what I am about to do).

Am I barking up the wrong tree? Is this just a simple matter of there being no shortcuts to understanding the basics?

Many thanks in advance for what I am sure is a common set of questions.

Kent

 

your circuit is fine to test servo. if you turn potentiometer by hand, duty cycle changes and servo goes to another position.

but you need also another timer to generate delay.

 

I figured it out.

The circuit is fine. I was originally using a LS-0006 servo which is not standard in terms of its pulse width requirements. I plugged in a Tower Pro MG90S and it worked immediately.

FWIW, the 68kΩ resistor works fine. I tried swapping it with a 2.7kΩ and it buzzed.

I'll post the exact schematic and parts list in a day or so.

Kent