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Servo Trigger Hookup Guide 

 

Introduction

The Servo Trigger is a small board that helps you deploy hobby RC servo 
motors. When an external switch or logic signal changes state, the Servo 
Trigger tells an attached servo motor to move from position A to position B.

The Servo Trigger in action.

To use the Servo Trigger, you simply connect a hobby servo and a switch, 
then use the onboard potentiometers to adjust the start/stop positions and 
transition time. You can use a hobby servos in your projects without having 
to do any programming!

In This Tutorial

This hookup guide starts with some background information about hobby 
servo motors. From there, it jumps into getting the Servo Trigger working 
with a small servo, then examines some of the inner workings. Finally, for 
the adventurous, it explains how to customize the Servo Trigger by 
reprogramming it.

Suggested Reading

• An Introduction to Motors.
• More information about hobby servo motors.
• Some background on Pulse Width Modulation.

Servo Motor Background

Page 1 of 14

Содержание Servo Trigger

Страница 1: ... the start stop positions and transition time You can use a hobby servos in your projects without having to do any programming In This Tutorial This hookup guide starts with some background information about hobby servo motors From there it jumps into getting the Servo Trigger working with a small servo then examines some of the inner workings Finally for the adventurous it explains how to customi...

Страница 2: ...ge ones used in industrial machinery An Assortment of Hobby Servos RC servos are reasonably standardized they are all a similar shape with mounting flanges at each end available in graduated sizes Servos often come with several wheels or levers known as horns than can be attached to the shaft to fit the device they are operating Example Servo Horns Electrical Connection Most hobby servos use a sta...

Страница 3: ...u re not using batteries the 5VDC available from a garden variety power supply is a good option If you re using the Servo Trigger to control your motor the absolute maximum supply voltage that should be applied is 5 5 VDC Regardless of how you re powering them it s worth noting that the current consumed by the motor increases as the mechanical loading increases A small servo with nothing attached ...

Страница 4: ...n one side possibly a small microcontroller Inside an RC servo The other side of the PCB has some discrete transistors probably in an H bridge configuration which allow the controller to steer current through the motor in either direction for both clockwise and counterclockwise rotation Back of the PCB One Other Useful Servo Ordinary RC servos turn over a 90 range it s useful for turning a steerin...

Страница 5: ... more specific use cases in the following sections Getting Started Quickly Let s jump in and build a circuit to show how the Servo Trigger works Materials and Tools You ll need to following materials to build this example circuit The Servo Trigger module A hobby servo motor we ll be using our micro size metal gear servo A switch any momentary contact switch is suitable so we ll use a 12mm tactile ...

Страница 6: ...in the previous section or consult the servo manufacturer s datasheet Then solder the switch wires to the IN and GND pads on the Servo Trigger and the power pigtail to the VCC and GND pads on the edge of the board These are mirrored on opposite edges of the board they re wired in parallel so you can use either set of pads The red wire should connect to the VCC pad and the black to GND Before we po...

Страница 7: ...ponents on the board and examine how it works The heart of the Servo Trigger is an Atmel ATTiny84 microcontroller running a small program that implements the servo control features we are discussing here Just because the Servo Trigger saves you from needing to write code doesn t mean that there s no programming involved The servo control signal is generated using a 16 bit hardware timer It runs of...

Страница 8: ...ications The default mode implements bistable control the servo will sit at position A or position B depending on the input actuation While the switch stays in a state the servo stays in the corresponding position it is stable in two different states Jumper Cleared Bistable Control This behavior can be changed by flowing solder between the pads of the jumper With the solder jumper closed the mode ...

Страница 9: ... active or asserted are used to describe when the input is being used and inactive or deasserted to describe the default state More components The servo trigger can be used with a wider variety of external components than used in the example above We used a mid sized servo though we have many other candidates in a wide variety of sizes torque ratings You can also use different switches such as mic...

Страница 10: ... motion when you actuate the input first check that A and B are not set the same otherwise there s no position change If you re feeding the input with a logic signal from an external device be sure to drive the signal for more than 50 milliseconds The PWM signal is updated every 50 mSec and events shorter than that may missed It s also possible to set T shorter than the time it take the servo moto...

Страница 11: ...or reprogram the IC You can use the command line WinAVR tools and program the board using an AVR Dude compatible programmer like our Tiny AVR Programmer If you re going this route Firmware ServoTrigger Debug contains the WinAVR compatible makefile Firmware Modifications Timing The range of transit times accessed by the T potentiometer is defined by a table of software values the table interprets p...

Страница 12: ...ased it moves back to A 2 oneshotFSM Does a complete cycle every time the input is asserted from A to B then back to A 3 ctpFSM A customization of the oneshotFSM for interactive artist Christopher T Palmer which allows the B to A return cycle to be interrupted by a fresh input actuation 4 togglingFSM Each time the input is asserted it changes from A to B or B to A This mode is especially useful fo...

Страница 13: ...m one function to another If your FSM is more ambitious it s still useful to read and understand how the FSM interacts with the rest of the firmware Your application may need a subtle variation of an existing FSM or a complete re formulation Since the source code is available you re welcome to modify it to suit your needs Resources and Going Further Now that you ve got your Servo Trigger running i...

Страница 14: ... Wikipedia has a very detailed article about Finite State Machines Page 14 of 14 3 29 2016 https learn sparkfun com tutorials servo trigger hookup guide _ga 1 235617985 193945 ...

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