Press "Enter" to skip to content

Maand: mei 2020

Duo-Pendulums Interacting

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-magnetic and electro-magnetic force fields combined with gravity. The weight of the pendulum is a magnet hanging horizontally from a needle. A sharp steel point makes a very low friction at the magnetic suspension point.
To count the runtime days of the pendulum I use a 6 digit lcd counter module. If the pendulum stops the counter resets. This gives me a true record of the ‘swing time’. A solar panel, a voltage regulator and a super capacitor provides energy for the ‘everlasting’ power supply.

Pendulum solar circuit, building plan and day counter

As coil pulse driver 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 and T4 is closed.

When the pendulum stops the basis of T3 becomes low and shall close this. 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.

The video shows how it is done
The active pendulum with solar panel, supercap, coil and daycounter

The duo pendulum project belongs to my investigation with micro- and nano powered moving devices. Before this I had to make many prototypes. It is important to make reliable electrical and mechanical connections. That sounds simple but is not. Double check is necessary. The active pendulum reacts jerky because of hidden magnets. There is no restpoint; the pendulum starts instantly. Watching a pair of pendulums ‘dancing’ is pure fun.