The typical holiday animatronic will contain inputs, such as buttons and light/motion sensors, and outputs, such as motors, lights, and speakers.

Learning to identify the parts of your animatronic will aid you in transplanting your own control system.

Motors

The key things to determine about motors are: motor type, voltage requirements, and current draw.

You can read more about different common motor types here.

The vast majority of animatronics from the store will contain brushed DC motors. These are perhaps the "dumbest" of the motor types you'll encounter, as they cannot be told to go to a particular rotational setting the way hobby servos and stepper motors can.

You can typically identify them by their shape -- a metal cylinder or flattened cylinder, with a plastic end cap.

In the Eyeball Doorbell example, there are two brushed DC motors, one to open and close the eyelid and another to rotate the eyeball from side to side.

They are geared down with a pulley and belt system.

Another tell-tale sign of a brushed DC motor is the capacitor soldered across its leads to help reduce electrical noise in the overall circuit.

Voltage

Using a multimeter in DC voltage measuring mode, we can see that the Doorbell sends approximately 4.5V maximum and approx. -4.5V minimum voltage to the motor during operation.

The three AAA batteries supply 4.5V, (1.5V x 3) so this makes sense, and is often another clue as to power requirements, although this can be misleading if the original circuit employs a buck or boost converter.

Current Draw

You also want to determine the maximum current draw of each motor so you can use a power supply or battery pack that provides enough current.

Use your multimeter in current measuring mode (this may require switching one of the test leads on some meters) connect one lead of the motor to the original controller board and the other from the board, in the multimeter's positive lead, then from the multimeter's negative lead to the motor.

Run the animatronic cycle and read the maximum current draw. In this case it is about 212 milliamps.

Measure the greatest draw a motor will pull -- the eyelid motor in the doorbell spins, then stays held with the lid open, drawing peak current.

Both motors combined draw a total maximum of about 250mA, so we'll keep this in mind when picking a motor driver. (Hint: The Crickit can handle this with no problems!)

Speaker Impedance

Typical toy/animatronic speakers are either 4Ω or 8Ω speakers, and this is often marked on the back of the speaker.

If not, you can usually measure the DC resistance of the speaker to get a ballpark idea of its impedance.

Unplug the speaker from the rest of the circuit first, then use your multimeter in resistance measuring mode to determine the impedance. In this case, a measurement of 7.4Ω is close enough to say it is an 8Ω speaker.

This means you'll need to use an amplifier that can drive an 8Ω speaker, which happens to be the case with most of the Adafruit amps! (They tend to drive anywhere from 4Ω - 8Ω speakers.)

Input

The trigger for the Doorbell is a simple momentary pushbutton switch. That's about as easy as it gets to re-use! You'll simply use the switch to control a digital input, by connecting the switch to a GPIO pin on the microcontroller (or Crickit) and ground.

If you're faced with a more elaborate input, such as a PIR sensor for motion detection, you may need to test the signals with a multimeter or scope to determine what signal is sent when the trigger is tripped. Often this will still be a simple digital high/low signal, which is easy to integrate, pretty much the same as the momentary switch.

LED Light

If your animatronic contains simple LED lights, you can drive them from a digital output or PWM pin to blink or even fade them. These will look like the typical two-legged LED (although they are sometimes a bit hidden as in the doorbell eye example here).

If the animatronic does multicolored lighting with RGB LEDs they will be either analog or digital (NeoPixel-style) packages.

You can determine if a four-legged LED is analog or digital by measuring the voltage between the power leg and each of the three other legs. If they are each operating at roughly 1V-3V, you've probably got an analog LED on your hands, and can control them in the manner shown in this guide.

If not, you may be dealing with a NeoPixel or similar LED.

If the existing LEDs seem daunting to control, you may consider swapping them out for your own NeoPixels.

This guide was first published on Nov 10, 2021. It was last updated on 2021-11-10 12:07:29 -0500.

This page (Animatronic Anatomy) was last updated on Nov 28, 2021.

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