Sola(r)Dex
The concept of the Sola(r)Dex is to combine a solar panel (photovoltaic panel, PV), a DC motor, capacitors wired in parallel, an analog circuit with MOSFET as a switch, and a cylindrical carriage to randomly cycle through a set of card.
The PV would gather light and the capacitor bank. After the minimum threshold of the MOSFET is reach the capacitors would release the stored energy to the motor which would turn until the capacitors are drained. The amount of rotation is inconsequential in this case because the desire is for the stopping position to be random.
Some of my research thus far has been figuring out the amount of capacitors I need in order to run start the motor. I’m thinking to use a a bank of capacitors wired in parallel. This will allow me to adjust the capacitance incrementally to find what works best.
The other difficulty has been finding the best way to release the stored energy at the right time. I didn’t want to use a microcontroller to do this, although it would be easier in theory. I think using a MOSFET and a few diodes will act as a voltage trigger. In this case I’m using a MOSFET with a threshold of 7V. The DC motor has an operational range of 2-7.5V, with a rated voltage of 6V.
All parts are listed in the BOM at the end of this post.
The about circuit diagram can found here: https://www.electronics-tutorials.ws/transistor/tran_7.html
There are a couple of important aspects of this circuit, a flywheel diode disperses any back emf produced by the motor to reduce the possibility of damage to the MOSFET. And a Clamping Network, a zener diode in series with a diode, to allow for faster switching.