Gentleheart

Most npn transistors will work.

An Arduino Mega with a few ws2812b ledstrips may be an option. Do you need RGB leds or just a single color led matrix?

Well you would actually have to consider the voltage drop of the diodes with this scheme.

Here are some tinkertoys I have made in the past to reduce breadboard space.

Nicely written and very useful tips. Thanx for taking time off for this from your gps-guided laser cutter. This may aid in building my time-inverted quantum displacement chamber. :-)

And right you are. Never knew the curie temperature of neodymium was that low. But for ferro magnets it is much higher. (>750° C) Not 3 times higher than soldering temperature but almost twice.So I stand corrected and the advice is to use ferro magnets for this project.

My bad: yes DS3231 RTC of course.

Brilliant idea! Surely will try this out!

Added bonus: the magnet will disappate some of the heat from the soldering iron.

The demagnetisation temperature of a magnet is wayyyyyyy beyond soldering temperature (a least 3x higher). No worries there!

A timer is not required if the meter displays the Ah or mAh. That is also a timer-indication: 1000 mAh = 1000 milliamperes for 1 hour.

Lookup 74HC595 (shift register) or PCF8574 (I/O expander) ic.For this you need a microprocessor (Arduino or other) to regulate it.For the 4017 you may need a NE555 to regulate it.

Just adding a photoresistor (LDR) between the batteries and the led would probably do the trick.A nicer solution is an LDR with a NE555 chip. That way you could also add a timer (auto shut-off after a certain time) I could provide you with a simple schematic for this.

I could design a timer like that for you with an Arduino, a ds3231 realtime clock module and a relay. Total cost would be $10 -$20.You would also need a 5v power supply, a us/eu/au(?) plug, a us/eu/au socket and a small (waterproof?) box to build a housing.Of course you could also opt for a more elegant solution with a display and some buttons so you can reprogram the timer without a computer. (Will not cost that much extra, but takes a bit more programming and wiring)

I can only imagine what the reaction at the post office would be if this was sent by mail. LOL.I think it would be fun to make this for you, but I live in Europe so that's not an option. Maybe you can come pick it up and take it on the plane back home. LOL.But if you would make this with e.g. an Arduino you could even make the display do a countdown and beep for the last ten seconds. I could design something like that for you but then you would still have to build it yourself.

Very nice idea, nicely made.I might use the idea with a little less leds but with rgb leds and build it with a sunrise feature (connected to an arduino-based alarm clock) I will also add an mp3 player and speakers to the shelf. This way your idea and mine will merge very nicely. Thanks for the inspiration!

Very nice project.Wouldn't be much of a problem to use thru hole components with this design now would it?Also: not really sure how to modify the board for the LM1117 and the L7805...

also very interested in attiny but the absence of i2c is a big issue for me.

My girlfriend has toys too but those cannot be turned down with an added resistor. Sometimes I wish I could add a resistor to the girl herself, but she is irresistable! ;-)

Very nice project. If you use a ds3132 rtc module you can lose the dht11. The only thing you would lose is the humidity sensor: Temperature is also available on the ds3132. Also it would keep much better time than a ds1302 module.

nice! What a coincidence that I have made exactly the same gadget for 4x 18650 batteries!

You could have said this a little more subtle. If you start low and don't go to high on the resistor value you will not break anything. Especially when there is no volume control on the toy it self. Try at your own risk but start with low resistor values. Volume control on an amplifier is often nothing more than an adjustable resistor.

Nice share. Though it's a very simple hack, it will surely help some frustrated parents. One advice: start LOW (<100 ohm) on the trial resistor values. If there is some volume control on the toy, glueing the volume control stuck at the desired level is a safer option.

I love this tutorial! Never knew the Arduino had build in pull up resistors: so much easier, projects with less components. Also love the interupt example: very educational.