Electronics
Initial Circuit Design and Part Orders
Our goal is to have our yo-yo light up when it spins. After
looking at previous LED backlit Yo-Yo designs we settled on the Roller-Ball
Tilt Switch as our mechanism for turning our circuit on only (in theory) when
the Yo-Yo spins. There is a conductive metal ball inside of the switch’s
cylinder that will short the leads, completing the circuit, when it rolls to
the bottom of the cylinder. If we orient the switch with its contacts pointed
radially outward the ball will short the leads when forced outward while the
yo-yo is spinning. With only one switch this is not of very much benefit to us;
whenever the yo-yo is held with the switch below the central horizontal axis
the yo-yo will light. This is unfavorable because the yo-yo would have to be stored
carefully to avoid draining the battery. If, however, we put two of these
switches in series and opposite each other, both pointed radially outward, only
one ball will be able to contact at a time unless the yo-yo is spinning.
Above: Circuit diagram.
The circles are our 5mm LEDs, the central red circle is a coin cell battery,
the two rectangle are our switches (in series between the battery’s ground and
the LED ground ring), and the grey outlines are the inner diameter of our yo-yo
and, inside of that, our circuit boundary).
We have developed a circuit for
testing and ordered the parts to do so. Below is a basic schematic (for the
purpose of calculating necessary voltage sources and current-limiting
resistors).
I have ordered an assortment of 5mm Super Bright Water Clear
LEDs- the bulk price
was fairly good (300 LEDs for $13), and the assortment of colors will satisfy all
members of our team (the one thing we could not agree on was a single color; we
could, however agree that multiple colors [a single color per yo-yo] would be
awesome). The circuit will be essentially the same for all colors, although the
voltage drops are split into two different ranges depending on color, so we
will have two different resistor values for optimal brightness.
Color
|
Forward Voltage (V)
|
Red
|
2.0~2.2
|
Green
|
3.0~3.2
|
Yellow
|
2.0~2.2
|
Blue
|
3.0~3.2
|
White
|
3.0~3.2
|
Purple (UV)
|
3.2~3.4
|
Above: Forward voltages for various colors of LEDs. For
the purposes of resistor calculations I split them into two forward voltage
categories: 2.2V and 3.2V.
The recommended current is 20mA. The voltage source is made
up of 3V coin cell batteries. We will likely need two per yo-yo for the 3.2V
LEDs (and may just go ahead and use the same for both for continuity). Using Ohm’s Law, R=V/I, I found that the resistors should be 30Ω for a 3V source
and 2.2V drop, 190 Ω for a 6V source and 2.2V drop, and 140 Ω for a 6V source
and 3.2V drop. I ordered 200 Ω resistors for testing purposes, as 190 Ω is an
unusual resistor value. Additionally, we will need 200 Ball Tilt Switches (two for each of our 100 circuits). I ordered 230
to account for errors on our end and switches that arrive broken. Everything is
scheduled to arrive over Spring Break which will give us time to test and
optimize our circuit.
Expenses
Item
|
Amount
|
Cost ($)
|
22 AWG Solid Wire (Hook Up
Wire)
|
25 feet
|
4.70
|
CR2032 Lithium 3V Batteries
|
50 batteries
|
5.25
|
LED Assortment Kit
|
300 LEDs
20 each R,Y,G,B,W,UV
|
12.99
|
Ball Angle Tilt Vibration Switch (SW-520D)
|
230 switches
|
49.87
|
Resistors (200Ω)
|
100
|
1.49
|
Total
|
|
74.30
|
|
|
|
|
What still needs to be ordered/tracked down: solder, copper braid,
and violet LEDs (the LEDs can wait until we get our initial circuit working).
