Asking for help to create a simple circuitboard

It will need some form of rather more complex, active electronics to make it work as you want it to.

Any really simple current sensing circuit will reduce the voltage out of the charger, unfortunately, so it probably would not be able to properly charge anything.

What is the current rating of the charger output - or the current input rating of the device being charged?

Photos of the charger and whatever it charges would be useful.


Connecting a LED in series with the output will reduce the voltage by anything from about 1.8V to 3V or so, depending on the LED colour.

What type of "speaker" are you wanting to use? A simple loudspeaker needs an audio signal fed to it, to give a tone or beep. A piezo buzzer would produce sound as long as it had power connected, as those have the audio oscillator built in to produce the tone.

If it would be difficult to make it still charge, i could drop it. Because it would be just a secondary function, because right now when i connect LED to "+" wire - device doesn't charge. I don't mind that. Main function would be just to check if power comes from outlet to device. I could give you photo tomorrow.
Also a simple buzzer would be enough. Because the point of the circuit would be just to make sure power is there. But from what i know - speakers (even buzzers) need more components than just "+" wire, right?

A LED with a suitable value series resistor, eg. 180 or 220 Ohms for a red LED, connected across the 4.5V output, would show that power is on.

Likewise a small piezo buzzer could be connected across the output, however that would sound all the time power is on.

Many so-called "chargers" are just power supplies, and the actual battery charge control is in the device being charged.
(eg. Anything that charges via a USB socket).

However some devices do have the "intelligence" to control the charge in the external unit. If that is the case with yours, adding anything across the output that takes more than trivial power may upset the charging system.
For that type, I'd only consider an ultra-bright LED with a high value resistor so the current is very low (which keeps the brightness to a sensible level).

Is it for something that uses NiCd or NiMH cells? 4.5V would be a standard for three of those types of cells?