Parallax 27808 User manual

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Gimbal Joystick with Adapter (#27808)

This quad-bearing gimbal joystick provides a two-axis resistive output for controlling position, velocity,

tilt, etc., as an input device to various microcontrollers, including Parallax’s P8X32A Propeller chip and

BASIC Stamp family of modules. It may be used with microcontrollers that have analog inputs, with an

external ADC, or with resistor-capacitor circuits for a purely digital solution.

The Joystick comes pre-wired with a 6-wire cable and 1.5 mm plug. An adapter kit with a matching 1.5

mm socket is included, for convenient prototyping on breadboards or thru-hole boards. Simple soldering

is required to use the optional but highly recommended adapter.

Features

5 kΩ linear-taper potentiometer on each axis

Smooth ball-bearing action on both axes

Selectable spring return-to-center on

vertical axis

Selectable detents and/or friction on

vertical axis

Adapter kit for 0.1” spacing is included for easy

prototyping (simple soldering required)

Specifications

Power Requirements: Passive device; will

work with any low-voltage supply

Interface: Resistive or voltage divider output

Dimensions: 2.70 x 2.32 x 2.42 in

(68.6 x 58.9 x 61.5 mm)

Application Ideas

Game controller

Remote control for robotics

Manual control for interactive displays

Packing List

Quad-Bearing Gimbal Joystick (#27806)

Adapter Kit (#27809) (including PCB, two 3-pin headers, and 1.5 mm 6-connector socket)

Resources and Downloads

Find example code, the latest version of this document, and additional resources from the Gimbal Joystick

product page. Go to www.parallax.com and search “27808”.

Adapter Assembly

Using the adapter kit is optional but highly recommended. The example wiring photos in this document

assume you are using it. The underside of the adapter board PCB is labeled as shown at left. The top of

the adapter board has pads to solder the 1.5 mm socket in place, as shown at right.

(1) Put on your safety glasses!

(2) Begin by inserting the short ends of the 3-pin headers into the PCB from the underside.

(3) Solder the 3-pin headers in place from the top of the board.

(4) Solder the 1.5 mm socket in place on top of the board.

Quick-Start Guide

Voltage Divider Circuit

The voltage divider is most basic circuit using the joystick:

Horizontal 5K Pot

Vertical 5K Pot

GRN

BRN

ORG

YEL

BLU

BLK

Quad-Bearing Gimbal Joystick

Vdd

Horizontal Output Voltage

Vertical Output Voltage

The horizontal output voltage will increase as the joystick moves from left to right, from about 0.38 * Vdd

(full left) to 0.63 * Vdd (full right). The center voltage is approximately Vdd / 2. The vertical output

voltage covers the same range, increasing from bottom to top, with the center voltage also being

Vdd / 2.

The horizontal and vertical output voltages can feed to an analog-to-digital converter (ADC) directly for

use with either a P8X32A Propeller chip or a BASIC Stamp. Parallax modules that supply two or more

channels of on-board ADC include the following:

•Propeller Activity Board (#32910)

•Propeller Board of Education (#32900)

•BASIC Stamp 2pe Motherboard (#28300)

It is also possible to read the voltage outputs via the Propeller’s sigma-delta ADC. (See Parallax Appnote

#AN008.) The following products provide two sigma-delta ADC channels each:

•Propeller Backpack (#28327)

•S2 Robot “hacker port” (#28136, #28336)

In addition, one can deploy an external ADC, such as the MCP3202 (#604-00060) in conjunction with a

BASIC Stamp or any other microcontroller.

Propeller Microcontroller Example

The wiring diagram below is compatible with the Propeller Activity Board and the Propeller Board of

Education. Both of those boards have an ADC that uses +5V for full-scale reading, rather than Vdd.

However, the two boards use different ADC models, so example code may not be compatible for both

boards. Propeller C code is provided for the Activity Board, and Spin code is provided for the Propeller

Board of Education.

Connect the joystick to the breadboard as shown below.

Propeller C Example Program for Activity Board

The example code from the Propeller C Tutorials series, written for a smaller joystick, works fine with the

Gimbal Joystick wiring example shown above by simply updating the ADC channels used. This example

program and the libraries it uses are included with the SimpleIDE software. Download for Windows or

Mac from http://learn.parallax.com/propeller-c.

In the SimpleIDE software, browse to Learn>Examples>Devices>Joystick, and open the project. Update

the first two lines in the while(1) loop to use ADC channels 1 and 0 as shown in bold below, instead of 2

and 3.

Joystick.c

http://learn.parallax.com/propeller-c-simple-devices/joystick

#include "adcDCpropab.h" // Include adcDCpropab

#include "simpletools.h" // Include simpletools

int main() // Main function

{

pause(1000); // Wait 1 s for Terminal app

adc_init(21, 20, 19, 18); // CS=21, SCL=20, DO=19, DI=18

float lrV, udV; // Voltage variables

while(1) // Loop repeats indefinitely

{

udV = adc_volts(0); // Update to Check A/D 1

lrV = adc_volts(1); // Update to Check A/D 0

putChar(HOME); // Cursor -> top-left "home"

print("Up/Down = %.2f V %c\n", udV, CLREOL); // Display voltage

print("Left/Right = %.2f V %c\n", lrV, CLREOL); // Display voltage

pause(100); // Wait 1/10 s

}

Click the Run with Terminal button. The SimpleIDE Terminal will show the voltage values returned for

each axis. As you move the joystick around, you will see the values change. These values may be used

as-is, or scaled to appropriate input values for the device you would like to control with the joystick.

Spin Example Program for Propeller Board of Education

Download and unzip the Gimbal Joystick Example Spin Code (search 27807 at www.parallax.com). Open

the program PropBOE_joystick_demo.spin with the Propeller Tool (a free download from

www.parallax.com/propellertool):

CON

_clkmode = xtal1 + pll16x

_xinfreq = 5_000_000

OBJ

pst : "Parallax Serial Terminal"

adc : "PropBOE ADC"

joy : "joystick"

PUB start | rawh, rawv

pst.start(9600)

joy.setup(0, 400, 500, 600, 50, -500, 500)

joy.setup(1, 400, 500, 600, 0, 0, 1000)

repeat

rawh := adc.in(0)

rawv := adc.in(1)

pst.str(string(1, " Raw Joystick", 11, 13, "Horiz:", 14, 7))

pst.dec(rawh)

pst.str(string(" ", 14, 15))

pst.dec(joy.value(0, rawh))

pst.str(string(11, 13, "Vert:", 14, 7))

pst.dec(rawv)

pst.str(string(" ", 14, 15))

pst.dec(joy.value(1, rawv))

pst.char(11)

Load the program using the F10 key, and open the Parallax Serial Terminal via the F12 key. You should

see a display that looks like this:

As you move the joystick around, the values in the display will change to show its position. The Raw

values are the numbers read from the ADC. The joystick.spin object scales the raw ADC values to

produce the Joystick values. In this example, the horizontal values range from –500 to +500 and

include a deadband in the center, so that the spring-return value is guaranteed to be zero. The vertical

axis ranges from 0 to 1000 with no deadband.

Propeller Spin Object

The Spin object, joystick.spin, handles the scaling of the raw joystick data, transforming the

measurements into values that are more useful to a given application. The following graph illustrates this

process:

In this example of a center-return joystick, the input values can range from about 380 to 630. These are

rescaled to a –500 to +500 range, with a 50-unit-wide deadband in the center. See the object’s

comments for further details.

RCTIME Circuit

Lacking an analog-to-digital converter, it is still possible to measure the joystick position by timing the

discharge of a capacitor. Here’s the circuit, which is applicable to the BASIC Stamp family of products:

Horizontal 5K Pot

Vertical 5K Pot

GRN

BRN

ORG

YEL

BLU

BLK

Quad-Bearing Gimbal Joystick

0.1uF

220R

Horizontal

Vertical

To measure each wiper position, the attached microcontroller will charge that wiper’s capacitor by

outputting a high on the associated pin. Then it will tri-state the pin and let the cap discharge through

the potentiometer to ground and time how long it takes for the voltage to go below the micro’s input

logic threshold. The higher the resistance being measured, the longer the discharge time will be.

BASIC Stamp Example

The wiring diagram below is compatible with the BASIC Stamp Board of Education or HomeWork Board.

Connect the joystick, the two resistors, and the two capacitors to the breadboard as shown below.

Next, enter the following demo program into the BASIC Stamp Editor software. (Or, download 27808-

Gimbal-Joystick-Debug.bs2 from the www.parallax.com, search “27808”). The BASIC Stamp Editor

software is a free download from http://www.parallax.com/basicstampsoftware):

' {$STAMP BS2}

' {$PBASIC 2.5}

LR VAR Word

UD VAR Word

HIGH 4

PAUSE 10

RCTIME 4, 1, UD

HIGH 11

PAUSE 10

RCTIME 11, 1, LR

DEBUG HOME, "Vert: ", DEC UD, CLREOL, CR,

"Horiz: ", DEC LR, CLREOL

PAUSE 50

LOOP

Press the F9 key to load and run the program. You should see output that looks like this:

As you move the joystick around, the numbers will change with the positions of the horizontal and

vertical axes. These values may be used as-is, or scaled to appropriate input values for the device you

would like to control with the joystick.

Mechanical Adjustment

There are three mechanical adjustments possible which affect the operation and feel of the joystick.

Loosening or tightening the screws on the underside of the joystick labeled A, B, and Cin the photo

below, will effect these adjustments:

These are the possible adjustments:

•Screw A: Loosen for a spring return-to-center on the vertical axis. Tighten to disable the return-

to-center action.

•Screw B: Loosen to remove friction from the vertical axis. Tighten to add friction.

•Screw C: Loosen to remove detents from the vertical axis. Tighten to add detents.

Resources and Downloads

Check for the latest version of this document and example programs, including the joystick.spin object,

from the Quad-Bearing Gimbal Joystick product page. Go to www.parallax.com and search “27808”.

Revision History

Version 1.0 – original release.

Version 1.1 – clarified Spin and BASIC Stamp program example instructions.

Revision 1.2 – corrected circuit in picture on bottom of page 3.

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