HarryA

There are two types of USB power suppliers; the USB power supply and the USB power supply charger. It appears you are using the charger. Consider using a USB hub connected to the charger then connect your led/motion detector plus a simple LED device. The LED device would have a constant drain to keep the charger active? see for example(18ma). https://www.amazon.com/dp/B07RR3FQWF/ref=sspa_dk_detail_0?pd_rd_i=B07RR3FQWF&pd_rd_w=945qJ&content-id=amzn1.sym.0d1092dc-81bb-493f-8769-d5c802257e94&pf

Comparing the two data sheets they appear to be nearly identical. the MMBT3904's higher current rating may make it last longer.

Here is a circuit that may work for you. I have a 10k thermistor and a MJE3055. I could try it on a breadboard if you like; converting it to 12v.

That is most likely an internal factory number. Remember they do not want you to repair them but to buy new ones. There are a number of videos on youtube in regard to chargers. Search on " Black&Decker 18V Li-ion charger " for example: https://www.youtube.com/watch?v=c-pTziUV1as

I believe this is what you need: push botton switch.asc push botton sw.xcf

Is the action like this? I got to many cd's Are you comfortable using a micro-controller like an Arduino UNO? time: action switch 1 switch 2 0: hv pulses charge C1 at ca at cd S2's 1: C1 is charged to 24v at cd at cc 2: hv pulses applied to V at cb at cc 3: C1 drops to 17v at cd at cd S2's 4: hv pulses charge C1 at ca at cd S2's cycle repeats

What types of short period are you interested in? What divert times are you interested in? An inductor in series with the source and load would retard the current going out and when the magnetic field collapses there would be a back emf towards the source. A length of coaxial cable would form a delay line. If not terminated to match the cable at the load a pulse would be returned towards the source. see: analog delay line

I used an optocoupler between an Arduino Uno and a mosfet at 350 volts for an capacitor discharge ignition circuit.

VARIAC

Multi-turn pots makes it slow to make adjustments. As Vellerman did not use them perhaps you could replace the pots with good ones like Allen-Bradley pots. Beware of the various tapers that pots have. Check Ebay for good prices on Allen-Bradley pots from US suppliers.

Are you using the information from Jaycar site? There is lot of information on their web site in Specifications and Articles. https://www.jaycar.com.au/atmega328p-mcu-ic-with-arduino-uno-bootloader-and-16mhz-crystal/p/ZZ8727 The manual is here: https://www.jaycar.com.au/medias/sys_master/images/images/9794372567070/ZZ8727-manualMain.pdf

Forums like this one would be more useful for your questions. They have folks there that have a lot of combined experience. https://www.solarpaneltalk.com/

What code book? And why do you care? Unplug the refrigerator and plug it into one of these. https://www.ebay.com/itm/293616232230?_trkparms=amclksrc%3DITM%26aid%3D1110018%26algo%3DHOMESPLICE.COMPLISTINGS%d%3APL_CLK|clp%3A2047675

As this was in response to a previous post that was removed I will replace with a joke: Wife texts husband on a cold winter morning: "Windows frozen, won't open "Husband texts back: "Gently pour some hot water over it and then gently tap edges with hammer." Wife texts back 10 minutes later: "Computer really messed up now."

I would think these 5 volt and 5 or 8 ampere power supplies would be useful for micro-controllers, etc. https://www.sciplus.com/8a-5vdc-power-supply-65520-p