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CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Multiple RAM banks for the IR Remote Control Assistant 90 Silicon Chip Australia’s electronics magazine siliconchip.com.au 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