New cheaper version
Downloadjoystick.zip, Zip file containing images and txt files.
Introduction
With the introduction of RC simulators for the PC and also all of thePC based flight simulators that are around these days it would be very usefulto those of us that are more use to handling the joysticks on our RC transmittersto be able to use your own RC transmitter with it's mixing function (ifit has any) to control these programs.
This is the function of the PC joystick interface, it is for use withstandard PPM sets, not PCM sets. The basic idea is that you can remove thecrystal from your TX and , plug the lead from the joystick interface intothe buddy box output of your TX and the joystick connector into the gamesport of your PC. This interface will only work with programs that are writtento use the games port. The interface provides 2, 2 axis joysticks and 4toggle switches which replace the fire buttons found on PC joysticks. Ifirst designed an interface to do this about 5 years ago, it used all descretcomponents and was not easy to set up, so it was decided that it was notsuitable for publication. A second design based on digital potentiometersworked well and needed no setting up but was to expensive at the time becauseit needed 4 digital potentiometer IC's which were about œ7.00 each.Recently the cost of these IC's has fallen and also a dual version has comeout, so it is now a viable option.
The interface has been tested with both Futaba and JR equipment and thebuddy box connections for this equipment are given, but it will work withall makes of equipment that have a buddy box output, that gives a pulsestream output from the encoder. This can been found by reading the manufacturesinstructions, if they say that you need both TX's switched on but only onecrystal fitted or only one aerial extended (usually the instructor) thenthis is the system used by the interface. If the instructions say that youhave to have both aerials extended and crystals fitted to both TX's forthe same radio channel, then the buddy box system used by this equipmentis not compatible with the interface.
For this interface to work properly you must have a joystick / gamesport on your PC that will accept 2 joysticks, most of the games ports thatare included with sound cards seem to be OK, but a few early multi IO cardsused to only implement 1 joystick connection for cheapness. Check your instructionsand see if it say's that the games port can take 2 joysticks, it usuallysays that a 'Y' lead is required, but this is only to be able to plug 2standard PC joysticks into the port, it is not needed for the interfaceas it is all wired in the one 15 way plug.
Technical Bit
The input signal from the buddy box output is decoded by IC1, once ithas measured all of the channels it sends the value of the first 4 channelsto IC1 and 2, these devices are dual 100k digital potentiometers which arereplacing the pots in the PC joystick. PC joysticks usually use 220k potsbut only work from 0 to 100k due to the reduced rotation ( only about 90degrees), so the 100k digital pots work fine.
PIC12C508
The micro computer used in the interface is a PIC12C508 which has a RISClike CPU, and supports 33 instructions. The chip contains everything thatis required to form a fully working micro computer, it has 12 input or outputpins, 512 program memory locations and 25 bytes of RAM. This may not soundlike much but because of the RISC type architecture the resulting code canbe very compact. It also has a wide range of power supply limits, 2.5 voltsto 6.25 volts at less than 2mA, making it ideal for use in model avionicssystems.
Assembly
The unit only consists of 10 components and 4 switches, so there is verylittle that can go wrong. The only 4 components that need to be fitted thecorrect way round are IC1, 2, 3 and Q1. The correct orientation of these4 components can be clearly seen in the component layout drawing. The toggleswitches used only have 2 terminals on them, the switches all needed tobe fitted the same way round, when looking at the PCB as shown in the componentlayout drawing the switches should be fitted with the missing terminal positiontowards the top of the PCB.
The unit is housed in a small plastic box, the PCB is mounted in thebox using the 4 switches. This box can be fixed to the side of the TX withVelcro so that the switches can be operated without taking your hands fromthe TX.
The main components IC1,2,3 used in this design are CMOS devices andcan be damaged by static electricity. When handling these items it is advisableto take some basic precautions, do not wear clothing which builds up a staticcharge, or handle the item until needed and before you touch it, try totouch a water pipe which should earth any static charge you have built up.DO NOT connect yourself directly to the mains earth.
The lead that you need to connect the interface to your transmitter isshown in the accompanying drawings, I have only been able to test the unitwith Futaba and JR equipment and so these are the only makes of equipmentthat I have shown connection details for.
Testing Operation
Testing is very straight forward connect the interface unit to the buddybox output and plug the joystick connector into the games port of your PC.Switch the Transmitter on ( remembering to remove the crystal or TX module). If you are using it with a PC program that has it's own joystick calibrationfunction then use that to calibrate the program to use the interface. Ifyou are using a program that is running under windows 95 then use the functionin windows control panel to calibrate the interface for use with all programs.
If when testing the unit you don't get the stick movement matching themovement on the screen and your software does not allow you to change thisin the setup / configuration option then you can swap the functions aroundby moving the wires connected to pins 3, 6, 11 and 13 of J1. These wiresare the ones that replace the joystick potentiometers.
Other uses
As the interface is emulating 2 PC joysticks with their fire buttons,you could use any PC programming language that can read the values of thejoysticks and the status of the fire buttons to produce your own programfor may be recording your stick movements on a laptop to see what is happeningwhen you perform certain manoeuvres, the possibilities are endless, letme know of anymore uses you find for it.
And Finally
I hope that this PC joystick interface is of use to you, and that youhave gained an insight into the possible uses of the PIC range of microcomputer chips in the world of model avionics. If anyone is inspired intotrying to develop PIC based projects for themselves then please don't hesitateto write to me for advice or information about this wonderful little chip.
