Blinking a light is a wonderful feeling. Whenever I start a project, the very first thing I do is to make the system blink a light. That’s how I know the processor is running my code. When looking at a system, simple lights are the easiest parts to identify. These are the pieces that the designers want you to see.
I want to look at the lights more closely than you can by observing a toy from the outside, so I’ll use a digital multimeter (DMM) like the ones in Figure 2-1. I’ll use my DMM on the guts of the toys to see how the lights in each toy work. Before I start on the quadcopter’s remote control, BB-8’s LEDs, or karaoke’s disco lights, let me go over some DMM basics.
Note: You may also hear digital multimeters called DVMs, multimeters, or voltmeters. These other names have specific meanings, but they often are used interchangeably anyway. Analog meters exist, too. They look pretty and are sometimes cheaper, but they are trickier to use, so I strongly suggest getting a digital one.
Get to Know Your DMM
A DMM is an incredibly useful tool. For $30US, you can get a pretty good DMM (even though my first several were $5US DMMs, they would be good enough for everything in this chapter).
DMMs can measure different things, and throughout this chapter I’ll use the voltage mode to check voltages in different parts of each toy when it is powered on. In voltage mode, if you touch the DMM’s leads to two different points in a circuit, the DMM will show you the voltage across them. Since these toys are battery powered you won’t need the modes that are more than 20V. Look for 20V and 2V DC settings on your DMM. If you have those, always set your DMM to 20V first; if your DMM shows under 2V, then you may need to go down to 2V for more precision. If you don’t see those options, your DMM may be auto-ranging (whee!) so it will figure out what range you need automatically.
For working with these toys, I only use the direct current (DC) voltage mode, sometimes represented with a straight line over dashes, it’s what comes out of batteries. Alternating current (AC), sometimes represented by a wavy line, is what comes out of the walls.
Warning: Don’t stick your DMM probes (or anything other than a plug) into a wall socket unless you are really sure you know what you’re doing! You may electrocute yourself and damage your DMM.
When the toy is off (make sure the batteries are out or it may just be sleeping), I’ll use the audible continuity test mode to see what parts of each toy are electrically connected. This mode causes the DMM to beep when the probes are touched together. It also beeps when each probe is touched to an end of the same wire or trace on a board, which is why I call this beep mode. Determining the connections helps me figure out what drives a toy to light up.
Almost all DMMs have voltage and beep modes. Most DMMs have many more features which I’m going to ignore. Since DMMs are all different, I can’t tell you how to configure yours; reading the manual will help you use it effectively.
Lights in Toys!
Almost all lights in modern toys are light emitting diodes (LEDs). LEDs are generally safer, cooler, cheaper, longer-lasting, and more power efficient than incandescent light bulbs. A few toys may still have incandescent lamps, mostly in nightlights; we aren’t going to look at those.
While you may think about how you interact with devices as you play with them, the LEDs are how the devices interact with you. They tell you that the toy is ready or needs attention, how to orient yourself, and how or when to press buttons.
LEDs are on when there’s a voltage difference across them. If I wanted an LED to be on whenever a toy is powered on, then I could simply connect one side of the LED to power, which is the positive (+) voltage of a battery, and the other side to ground, the negative (-) voltage, through a current limiting resistor. I’ll discuss that in “The Taillight LED” later in this series.
However, if I wanted the LED to turn on or off depending on what the toy is doing, that gets a lot more interesting. The quadcopter’s controller LED does exactly that.
Quadcopter Controller LED
Whenever I power on the quadcopter controller, a red LED blinks on the controller. A blinking LED means the controller is waiting for the quadcopter to be powered on. After I turn on the quadcopter, the controller and quadcopter talk wirelessly.
As shown in Figure 2-2, the LED is big and domed so it is easy to find on the top of the controller board. It is also marked LED1 on the board in white lettering (which is called silkscreen).
It is easy to find the LED pins on the back as they go through the board (which makes them through hole parts). With the DMM in voltage reading mode, and the controller on, I can measure the voltage across the LED’s pins as shown in Figure 2-3.
Using the voltage reading mode, you can’t do a lot of damage to the board, as long as you are careful that each probe only touches one thing at a time (the same cannot be said for beep mode). And as long as you don’t touch the metal tips of the probes, you aren’t likely to hurt yourself either.
As the controller LED blinked, my DMM read around 4 volts (V) when the LED was on and 0V when it was off. This was interesting, as when I measured the voltage across the battery connections, the DMM read only 3V with mostly fresh batteries.
Where does it get more volts? Somewhere on the board is a part, called a voltage regulator, that boosts the voltage, probably there so the LED is brighter than it would be if they used the available battery voltage. The regulator also ensures that the LED doesn’t dim as the battery dies.
BB-8 solves this brightness vs. battery voltage problem in a different way, more on that next week.
This is a series. If you’d like to read them in order, check out the Taking Apart Toys index.