The BEAM Circuits Collection is a
Mazibug solar engines
An SE derived from a
As part of a thread of discussion on the Mazibug
photopopper design, Wilf Rigter wrote
up this description of the SE portion of the Mazibug 3
The Mazibug SE works much like a FRED SE; the
waveforms should help you get the picture. Assume TP1-TP3
are at 0V (the blue line in the waveforms) to start and
is just rising above the voltage
where the FLED
starts to conduct. The voltage
at TP1 is generated by the current
passing through R2 which is grounded at TP3. As Vcc
rises, the FLED starts to pulse and every pulse causes a
spike across R3. That voltage
spike is coupled through C1 to TP2. As Vcc
continues up, the LED
turns on and the DC
on TP2 starts to ramp up. The pulses from TP1,
superimposed on the DC
voltage of TP2, are used to "sample" the Vcc
level and at some point (~4V) the pulsed voltage
on TP2 crosses the 74AC240 threshold shown in the TP2
waveform with the green line.
When the 74AC240 is triggered, TP3 goes to Vcc
and R2 bypasses the FLED.
TP1 also rises to Vcc
and TP2 rises to Vcc
-1.3V=2.7V which is Vcc minus the voltage
drop across the LED.
drops to the reset level (2.6V) , the voltage
at TP2 crosses the 240 threshold level again and TP3 goes
to ground. Keep in mind that the 74AC240 threshold is
The 74HC, HCT, ACT types have lower thresholds and may
require some adjustment.
The value of R1 can be 100K-1M and the value of R2 is
between 5.1K-33K. For testing use a 1000 ohm current
limited 6V battery
supply to simulate the solar
cell and a 3,300 uF cap
for storage. Measure the voltage
on the cap with a voltmeter to determine the trigger and
reset levels. I used a NPN
transistor and a small motor for a load for these tests.
Remember, like the FRED design, the FLED
is sensitive to light and should be shielded. FLED
SEs always require some fiddling to get them going but
they do use commonly available parts. Of course a 1381
Mazibug would be much more predictable / reliable.
For more information...
You might also want to read the writeup on the
photopopper, as well as its original 74*14