electronic pendulum (self optimizing)

[micha1102b]

Hi there,

the solution given here for a simple electronic pendulum has some improvements over those around.
Maybe some of you can draw some inspirations for own creations to come:

- just a single coil (with number of turns and its geometry widely noncritical) is used, acting both as sensor and as actuator

- scaling up of the setup for much larger and more powerful implementations is easily done.

- the pendulum starts automatically (after an adjustable period of time), if no impulses are detected on sensor (I have attached a LDR to a free controller pin, so a complete switch off at dark is now an option)

- self-calibrating of the circuit. No matter whether the length of the pendulum is 10 or 250 cm - the swing width of the pendulum is always at its maximum

- the magnet can trigger the circuit at approach as well at distancing from the coil.
This allows for countless interesting software variants and experiments

- the controller detects the period of the pendulum and switches to power saving sleep mode whenever possible

- a LED flashes at each trigger event, resulting in a nice stroboscope effect if directed towards the pendulum

- the controller software is quite simple;
  1. at start an ADC gets the voltage on the lower end of the coil as initial value (i.e. pendulum not moving).
  2. within the endless loop the same ADC gets the voltage of same point by polling.
  3. this value is then compared with those initial value.
  4. if necessary, the transistor is driven to send a magnetic impulse of the coil by discharging the electrolytic capacitor, accelerating the magnet a bit.
  5. with variation of length and delay of the impulse the swing is getting maximized.

best regards
Micha

[perdrix]

Now all you need to do is to lock it to a GPS 1PPS signal 

[Gyro]

I don't think you actually mentioned the intended purpose of the pendulum (though I'm assuming timekeeping, but see below).

You would do well to look at the history of electric master clocks. 'Free pendulum,  Synchronome and Gents master clocks, Hope-Jones, the Shortt-Synchronome time standard clock etc. are good search references. Apart from being interesting in its own right, the elusive search for the 'Free Pendulum' has some interesting lessons. For instance it is not necessarily optimal to externally influence the natural swing of the pendulum on every oscillation, Making sure that the drive pulses doesn't vary in amplitude or duration at all (gravity escapements), making the arc of the swing small and predictable (amplitude control?) etc.

Gents also used their 'waiting train' tower clock movement as a very powerful and efficient externally time synchronised motor for driving heavy hands under high winds and icing conditions. Pendulums make very good motors!

Electronics, of course, makes the whole area of free pendulums a hell of a lot easier, but if you are seeking to produce an "electronic pendulum has some improvements over those around" then there are lessons to be learned from the past. Free pendulums are not only affected by friction and having to provide energy, but also in the influence of the maintaining energy that you put into them.

It is easy to see the effects of temperature and particularly atmospheric pressure variations - things that you could maybe integrate into your design using readily available sensors and possibly compensating them in the drive level (the wider the swing, the slower the pendulum, due to circular error). If you get all of the compensations right, you will be able to see the effect of 'Nutation', mainly the effect of the position of the Moon and tides affecting the local value of g.

A basic Synchronome example:

https://www.eevblog.com/forum/chat/what-did-you-buy-today-post-your-latest-purchase!/msg1154556/#msg1154556

[micha1102b]

I don't think you actually mentioned the intended purpose of the pendulum (though I'm assuming timekeeping, but see below).
....

Hi,
thanks for the very interesting thoughts and link.

To be honest: the main aim with this little project was actually not creating a time base.
I'd rather tried to find a SW-solution which automatically and autonomously maximizes the swing of a (magnetic) pendulum driven by a solenoid, for any given physical and electrical dimensions of the setup.

Basically, the SW has just to calculate and get the optimal value for length and delay of each single magnetic pulse.

Best regards
Micha

[micha1102b]

Now all you need to do is to lock it to a GPS 1PPS signal 

   

What about using this pendulum as time- and clock-base for all GPS ground stations and sats?
I would even sacrifice a free controller pin for this...