Step 3: Build the LED circuit (with tilt switch)
The six leds in the tube are connected parallel (all the led's plus-sides are connected, and all the minus-sides too). Use stranded (supple) wire to connect the leds, so they fit into the tube nicely later on. To connect the leds to eachother, I soldered 6 strings of wire pigtail, and then soldered the pigtails onto the led's leads. See picture 3 on how to do that. If it's not clear to you then, have a look here for a more detailed explanation...
Blinking LED circuit (pics 4 through 8)
The circuit that makes the leds blink (picture 4) is a very basic circuit around a 555 timer. This is not the most efficient way to do the job, because the 555 timer consumes a fair amount of energy just to stay alive. I used this scheme just because I had the soldered pcb lying around (it is a remnant from a previous I'ble I made). On the pcb a switch was soldered already. I replaced this switch with a roller ball switch.
This circuit should be turned on when the Sound Tube is set vertically, with the speaker-side up. A roller ball switch (or a tilt switch) takes care of this.
- Solder the components onto a pre-etched pcb. Cut the copper strips where marked with an X in the drawing (picture 5).
- Solder pieces of supple wire of about 8 cm (3") to the roller ball switch' leads.
- Eventually, solder the string of six leds to the pcb and test the circuit.
Powering the circuits
The voicerecorder and the led-blinking circuit are powered by the same 9 Volt battery.
I made a seperate, small pcb on which the battery's leads and a switch are mounted. The powerleads to and from the voicerecorder and led-blinking circuit are all connected to this pcb.
The switch is used only to shut down the Sound Tube completely.
Optional (picture 9): Leds fading in and out
What I really wanted was an array of leds that fades in and out. I spend hours trying different kinds of circuits, but none of them worked the way I wanted to. Making a led fade in was not so hard, but letting a led fade in and out without a microcontroller is truly a tricky task to accomplish...
Eventually, I got help from Jan Leisink, probably the best science teacher in The Netherlands. He came up with a circuit that almost worked the way I was looking for. After some tweaking, I got it right. Unfortunately, that was after the Epilog Challenge deadline, so that's why it's not in the Sound Tube I made.
Now, if you build the circuit in pic 9, chances are that it will not work just as you expected: The way the leds fade in and out depends strongly on the values / specs of four components in the lower left side of the circuit: The leds, the transistor, the capacitor and resistors. To make tweaking more easy, I put a variable resistor in the circuit. Adjusting it's value influences the way the leds fade in and out.
A big advantage of this fade-in fade-out circuit is that it is much more efficient in energy than the 555-timer circuit. So using this circuit will make the 9V battery last a fair bit longer. Give it a try, if you like.