regulator as it did not require a
heatsink. It puts out less heat and it's
more efficient for a wide voltage
input range. I ran the board for six
months in varying temperature
conditions (hot and cold) and not
once did the component overheat,
oscillate, or behave erratically. The
switcher is also a drop-in equivalent
to the LM78XX series in the TO220
case, so I did not have to change any
components in my PCB program.
2. The two resistors in parallal
were done for two reasons. The first is
heat dissipation due to the voltage
drop from 24 VDC to power the LEDs
( 2 VDC at 20 mA). This enables a
complete parts list using only 1/4W
resistors. Also note that the input
voltage is 24 VDC — fairly common
for industrial applications. Hobbyist
applications typically run at 12 VDC.
By removing one of the two resistors
where they are paralleled and
changing the output relay coil to a 12
VDC model, the board can now run
on 12 VDC without any other
modifications. So, the extra
components add some design
flexibility.
3. I have had a unit powered
down for over three months and I just
recently powered it back up. There
was no loss in data and the unit
picked right back up where it left off.
This is a result of two things: the low
current consumption of the time
keeper chip and the storage capacity
of the super capacitor. Based on
some quick math, the data in the
time keeper chip should be good for
a year of storage. This is based on a
RC time constant factoring in the chip
voltage and current consumption
combined with the 1.5 F capacitor.
Regards es 73 de,
Gerry Shand VE6BLI
60 November 2013
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