Intro to coding

[The Natural Philosopher]

Yes. A diode or two might be handy.

In fact a single relay should be possible to make a relaxation oscillator out of.

Consider: the relay has a fat capacitor across its coil, and its fed via the NC contacts from a suitable voltage source with a resistoir the same value as the coil.

As soon as its switched on, the volatge source charges up the capacitor and eventually switches the relay. The capacitor then discharges through the coil until.the relay switches again and the cycle repeats....

So that's one voltage source, one relay with NC contact at least, one resistors and one capacitor.

With a car flasher unit (old style) you just use a coil and a bimetallic strip...

[The Natural Philosopher]

No. you just need a large capacitor, See my explanation earlier

[Tim Watts]

I'm going to say yes.

In a way, old fashioned buzzers are just a relay wired through itself.

Add a capacitor a resistor and you should be able to make it oscillate at other (lower) frequencies.

Indeed.

That still leaves hydraulics :)

[Dave Liquorice]

I might have a play later, if I can find a suitable DC relay and big enough capacitor.

[gareth]

Back in the early 1970s (before most subscribers to this NG were even a twinkle in the milkman's eye?), the challenge was to produce a bistable flipflop with just two relays.

I don't remember the exact solution, but ISTR that it involved trying to prevent re-triggering when a steady level of excitation was present.

[Dave Liquorice]

Useful, yes, thank you. This course has three "Assignments" that have to be completed and submitted for marking by the distance learning company and the the certification comes from Edexcel. So I guess it's a reduced course of some sort.

He is finding some of it hard going as he has yet to do, at GCSE, what the course is assuming as knowledge from finished and passed GCSE's... As I say he's only in Year 10 (fourth year in old money) so working at or near A-Level is pretty damn good.

[Huge]

Now I know how non-IT geeks feel when us IT types start yammering away in the pub.

[Huge]

[John Rumm]

a 1/2) - I got the daughter to build an full adder out of 74 series logic...

e) Turn it into a wood working project:

[Tim Lamb]

AOL:-)

Mind, I helped my daughter develop a *brake lamp failure* indicator for her GCSE.

[Tim Streater]

Impressive! How many bits? Extra points for having it read 10-position rotary switches to represent the input decimal numbers, and drive a display showing the decimal result.

[Johnny B Good]

What, no resistors or diodes? Thankfully, the question posed seems to invite the use of 'relays' in the plural.

You *can* used "special" relays like the GPO used in telephone exchanges. A classic type that comes to mind for this use are the 'slugged' types which can provide a delayed operation as well as delayed release. However, by using more than just a pair of cross-linked relays, it's possible to gain modest 1/2 to 2 second delays[1] using 'ordinary' relays by arranging the coil windings to be in series with a resistor or another relay coil winding whereby a similar effect can be had by shorting the winding to achieve a delayed release.

It's been well over quarter of a century since I last clapped eyes on any N diagrams but I'm pretty certain it's quite possible to create a multi-vibrator from just two relays with pulse cycle times in the region of 1 or 2 per second.

[1] Of course, one could always use a cascade of relays to extend the time interval to several seconds. I've seen a set up using 4 relays this way to generate such delays (Istr it was an 'unofficial' setup to drive a string of flashing Christmas Tree lights, possibly a 3 or 4 phase arrangement of 50v carbon filament lamps to obtain a directional effect :- ).

[Tim Watts]

Oh that is so cool!

I love the cascade to the overflow bit :)

[Bob Eager]

I have to do both!

[John Rumm]

;-)

Just the three to start with...