Sun Tree

A circuit that uses a MC34164 voltage trigger that allows most of the capacitor energy to be used for the motor.

I cut pieces of an old PC board for a base. Mount sticky feet on the bottom.


Mount your components to the board by using the solder pads for support.


 The solar engine in this artbot uses a mosfet to dump stored energy to the motor.

A MC34164-3 senses the voltage across the capacitor C1.  When the voltage reachs 3 volts, the mosfet is turned on. To allow the mosfet to remain on till most of the energy is discharged, a capacitor at the gate keeps the mosfet on to .2 volts.  The diode D1 prevents the capacitor from discharging after VS1 goes high.  After VS1 goes low, leakage through the diode will discharge the gate capacitor and turn the mosfet back off.  Trimmer R1 sets the trigger voltage.  R2 is a pull-up resistor that turns on Q1 when VS1 is triggered.

Scope waveform showing voltage across capacitor C1. Useable range 3.8V to .2V

If pin 1 reset is connected directly to the mosfet without D1 and the gate capacitor, VS1 will reset to low too soon and not fully discharge C1 into the motor.

The capacitor does not discharge fully.

Not all the energy of the capacitor is allowed to go to the motor. VS1 resets too early.  Useable range is restricted from 3.8V to 3 volts.

In a second version, replace the capacitor with a small Nicad battery pack.  The solar cells will charge the battery, then the circuit will discharge the battery to a lower voltage  and then restart the cycle. C1 and D1 may be omitted.

Link for 2N7000 datasheet

Youtube video

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