The BEAM Circuits Collection is a
Wilf Rigter's SIMD1 V1
Part of a family of nocturnal
solar engines (all circuits on this page ©
Rigter ; note that the majority
of this explanatory text comes from either postings by, or
correspondence with Wilf)
SIMD1 V1 is functionally the same circuit
as SIMD1 V0 but provides an active
high signal to the load when night (or at least
darkness) has arrived.
SIMD1 V1 Basic Circuit
e = enable (active high); v =
g = Gnd
SIMD1 V1 Example Circuit
LED load with gate driving
As with the SIMD1 V0, a 100K - 1M
across the solar
cell helps with turnoff, but the SIMD1 V1 requires
almost complete darkness before switching.
In the example circuit,
the SIMD1 V1 is again shown driving a single LED.
This example (as with the V0
example) makes use of a 74*14 Schmitt
inverter to switch power on within the load.
Normally the active high output from the inverter
is used to enable the remainder of the CMOS
gates which then perform some useful function. When the
SIMD1 triggers at night, it snaps on and the output signal
can be used to control the 5 remaining 74HC14
inverters connected in parallel
with the outputs used as a "power" switch. Or the signal can
be used as the tristate control of a 74HC240
or be used as a PNC
input for an Nv
net etc. to apply the stored energy to the load.
A point to remember when adding on the rest of the
is that CMOS
logic draws considerable supply leakage current
when inputs are not at 0V or Vcc. That problem virtually
disappears when Vcc
<3V; as a result, this circuit
is only useful with a single 2.5V capacitor
and a lower voltage solar
cell. Also note that the example circuit
also has a somewhat high switching voltage when the
difference between the solar
cell voltage and the capacitor
voltage is sufficient to turn on the CMOS gate. A 74HC14
switches at a difference voltage of 2/3 Vcc.
In general, HC logic switches at 1/2 Vcc
and HCT logic around 1.8V.
eGroups beam and alt-beam mailing list
discussion on this design
SIMD1 V0, V1, and V2 are compared in beam
list message #95