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NBN backup battery
at 0. The game begins by pressing S7,
causing LED1 to flash randomly one to
three times and then remain on while
the sounder generates a beep. Once
LED1 is on, or the beep is generated,
all four counters start counting up in
milliseconds from 1 to 8000.
Now each player should press their
own pushbutton switches as fast as
possible to stop their relevant counters.
The fastest player to press their button
wins. Then the player with the quickest finger or the minimum reaction
time (the minimum counter value) is
announced as the winner on the LCD
screen (eg, “Winner: Player 4”). It’s possible to have multiple winners if the
buttons are pressed simultaneously.
In all three games, if a button is
pressed too early (in the start status
while LED1 is blinking), it will continue flashing, and the sounder will
beep until the button is released. Then
after another random flashing cycle,
LED1 will stay on while a beep is
made to signal to the players to press
the play buttons to resume the game.
If one or more buttons are not
pressed within eight seconds (8000
milliseconds), the counters stop at
8001. The display will then clear to
show “Timeout Error” on the first line
and “Press start button to play again”
on the third and fourth lines. To reset
and restart the game, press S7.
The software for this circuit can be
downloaded from: siliconchip.com.
au/Shop/6/6339
Mahmood Alimohammadi,
Tehran, Iran. ($80)
siliconchip.com.au
Having recently had the NBN
installed, I found that now I had two
devices (the NBN modem and the
wireless router) both powered by plugpacks and both dependent on mains
power to keep working. We get the
occasional blackout in my area, and
without these devices, I have no internet connection on my tablets and other
battery-powered devices.
Reading past articles in Silicon Chip
inspired me to design a simple backup
power supply. The circuit operates as
follows. The mains power supply is
connected via CON1. I used one of the
NBN plugpacks (12V DC).
IC1 is a precision adjustable shunt
regulator, but is being used here as an
open-collector comparator with a precision voltage reference connected to
one of its inputs.
With voltage across CON1, transistor Q1 is switched on and it pulls
the reference input of IC1 low. This
prevents IC1’s output transistor from
conducting, so Q2 is off, and the only
path to output connector CON3 is from
CON1 via schottky diode D1.
LED1 is also lit as it is powered
from the DC supply, indicating normal operation.
When the plugpack voltage disappears, as long as the battery voltage
is above 9.25V, IC1’s reference input
is allowed to rise above 2.5V. So IC1
sinks current from its anode terminal,
switching transistor Q2 on, supplying
the output from the backup battery.
Australia's electronics magazine
Since I used a lithium-ion battery
as the backup battery, I needed to be
able to disconnect the output if the
backup battery voltage fell below
9V. You would probably change the
27kW resistor to 33kW for a lead-acid
battery, raising the cut-out threshold
to 10.75V.
The green LED indicates that plugpack power is available, and the red
LED indicates when the output is supplied from the battery. If both LEDs are
off, there is no output voltage.
This circuit does not include any
way for the battery to be charged,
because where I live, power outages
are infrequent and I am happy to
recharge or swap the battery manually
every few months.
If you need to keep the battery
charged, you can permanently connect
a mains trickle charger (for lead-acid
types) or lithium-ion maintenance
charger to the battery.
D1 should be a schottky diode of
sufficient rating for the load current.
Transistor Q2 can be any PNP transistor rated for the output current; something in a TO-126 or TO-220 package
will do, and it does not have to be
heatsinked.
I built my version on stripboard and
housed it in a small plastic box. Of
course, this can be adapted for many
other uses where a simple backup supply is required.
Robert Budniak,
Denistone, NSW. ($80)
April 2022 91
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