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I liked the idea of recording macros
using your IR Remote Control Assistant (July 2020; siliconchip.com.au/
Article/14505), but I wanted more than
eight buttons so that I could merge several remote controls into one.
As I could not change the firmware to add extra buttons, I decided
to switch the RAM chip instead. Each
chip holds IR code sequences for up
to eight pushbutton switches.
To do this, I added a small PCB (34
x 31mm) which sits over the existing
PCB and holds the extra RAM chips,
plus a switch to select which one is in
use at any given time.
There is a choice to expand the
Remote to 16 buttons, using a DPDT
switch (S2) and one more RAM chip
(IC3), or 24 buttons, using a 3PST
switch (S1) and two extra RAM chips
(IC3 & IC4). The PCB has provision for
either switch, as shown on the circuit
diagram.
The 100kW resistors pull the unused
RAM chip CS lines high, disabling the
unused chips and maintaining the low
current drain on the battery. Switch S1
or S2 pulls one CS line low at a time,
enabling the selected chip.
The Gerber files for the add-on board
can be download from siliconchip.
com.au/Shop/10/5913
Robbie Adams,
Tauranga, New Zealand. ($100)
The IR Remote Assistant PCB
needs the track cut between
pin 10 of IC1 and pin 1 of IC2.
This location can be seen in the
diagram at right. The addon
PCB is then seated on top of
this main PCB, as shown above.
Solar garden light uses supercapacitor
We purchased quite a few solar garden lights which each have a small
solar panel and a battery to store the
energy collected during the day, powering a small LED for 5-6 hours at night.
These worked well for one year, then
the battery started deteriorating, and
finally it stopped working altogether.
So I thought, why not replace the
battery with a supercapacitor? From
a good supercapacitor, you can expect
a lifetime of 20 years, irrespective of
the number of charge cycles while a
storage battery has a maximum life of
2000-5000 cycles.
I built this circuit with three LEDs,
and it runs for a whole night without
totally discharging the capacitor. The
supercap is charged from the cell via
schottky diode D1, which was chosen
due to its low forward voltage drop.
While there is voltage across the cell,
siliconchip.com.au
PNP transistor Q1 is held off as its base
is pulled up close to its emitter.
At night, current can flow in reverse
through the cell. D1 stops the supercap from discharging through this
path, but the base current for Q1 flows
through the 5.6kW resistor and the cell,
powering the LEDs. The 470W resistor
limits their current to around 4mA
([5V – 3V] ÷ 470W). All the components cost me less than $4.
Editor’s note: keep in mind that the
energy storage of the supercap is considerably lower than even a relatively
small rechargeable battery. While the
LEDs probably will produce light for
many hours, they will be quite dim
after about one hour, with the current
dropping from about 4mA initially
down to around 1mA after 60 minutes.
Bera Somnath,
Vindhyanagar, India. ($80)
Australia’s electronics magazine
September 2021 91
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