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.
