The aim of this project is to cause a continuous swing of 2 pendulums. I discovered a nice interplay between an active and a passive pendulum. It is an interaction of permanent- and electro magnetic force fields combined with gravity. The weight of the pendulum is a magnet that hangs horizontally from a needle. A sharp steel point has almost no friction at the magnetic suspension point.
To count the days that the pendulum swings I use an lcd counter module. When standstill the counter resets. This gives me a true record of the ‘swing time’.
A solar panel, a voltage regulator and a super capacitor provide the everlasting power. Time will tell how long that is...

The pendulums are simply constructed. A wooden board, a bow of aluminium strip, a mattress needle, a piece of glass and 3 magnets. The bow is connected with messing screws to the board. The only iron part is a 10 inch mattress needle with a sharp point. Make this on length. Magnets are of the 10 x 10mm round type. The magnet weight is connected to the needle with a copper plate . Connect the glass plate with second glue below the top and put the magnet with double sided tape on top. Make four small stick-on feet to the bottom plate.  

Electric circuit:
As coil pulsedriver I use my simple 2 transistor circuit. Variable resistor RV is set for a clean pulse. The LED lights up by the back EMF. NPN transistor 2N3904 is reversed connected; this works fine, try it! I have extended this circuit with a day counter. I use a low power Trumeter 7000AS as totaling counter with reset and up/down direction function. The count input C is connected with the solar panel and is negative edge triggered. By night the voltage falls below the 0.7 threshold and the counter will add one step. Reset at input R happens also on the negative edge.

In the active state the pulse circuit feeds a positive pulse (via C 100nF and the schottky diode) at C 470nF. Transistor T3 is in conduction. Capacitor C 100uF is shorted and T4 is closed. The reset input stays high.
When the pendulum stops the basis of T3 becomes low and will close the transistor. After C 100uF is charged T4 is in conduction and this will reset the counter. The circuit uses as little as 30uA, inclusive day counter. The supercap will charge even in cloudy conditions and indoor light. The 3V regulator is an ultra low power SMD type.



Watching a pair of pendulums, moving in a kind of dance, is fun. It's like an on-going dance party on my windowsill. To come to this result, the corona lock-down was helpfull. To make devices that work over a long time, lets say 10 year, is not an easy thing. Many prototypes have been made and demolished. You cannot see electric-, magnetic- or gravity forcefields. My gaussmeter and scope are a godsend.

A free swinging pendulum is much more fun. The secret is a horizontal hanging magnet as weight. My first discovery was the double spin pendulum. It runs like the rotor of a motor in a swing. This random pendulum reacts very jerky because the hidden magnets. The coil and the counter are the only hard to get parts. This is also an on-going investigation on micro- and nanopower powered moving devices.