Download lead.zip, Zip file containing images and txt files.

Download lead.pdf, Acrobat version of orignal article.

Ordering PIC's (IC1 and IC2)

Introduction
This article is going to describe a unique new buddy box lead; this lead will allow JR/Futaba transmitters to be connected together.

The inspiration for this project as with some of my other projects in the past came from a series of discussions in one of the Internet news groups that I use. Someone asked about connecting a Futaba and JR transmitter together via the buddy box sockets for training purposes and he got a lot of replies saying 'no you can't do that it's impossible'. Well always being up for a challenge I decided to have a look at the problem and see if it was possible.

Both JR and Futaba have very similar buddy box systems the only differences are the signal levels and that the first three channels are in a different order. It was the channel order problem that was stopping most people from staying yes you could do it so that was the main problem to crack, the result of which is presented here.

Changing the level is no real problem and can be achieved with some simple electronics, but changing the order of the pulses is a bit more difficult and will require the use of some computing power. In this design it was decided to use two PIC12C508 as two tasks are needed too be done simultaneously, measuring the input and generating the output signal.

Channel Squence

Radio Make	Ch1	Ch2	Ch3	Ch4
Futaba	Aileron	Elevator	Throttle	Rudder
JR	Throttle	Aileron	Elevator	Rudder

The Technical Bit

The input signal from the buddy box output of the slave transmitter is measures by IC1, once it has measured all of the channels it waits for the sync period sends the values of the measured channels to IC2. IC2 then generates the same number of measured channels but swaps the order of the first 3 channels to match the master transmitter that is being used, this is set by the state of LK1. IC2 then generates a sync period while it waits for the next data to be sent from IC1 and the whole process starts again.

The PIC12C508

The microcomputer used in the interface is a PIC12C508, which has a RISC like CPU, and supports 33 instructions. The chip contains everything that is required to form a fully working micro computer, it has 6 input or output pins, 512 program memory locations and 25 bytes of RAM. This may not sound like much but because of the RISC type architecture the resulting code can be very compact. It also has a wide range of power supply limits, 2.5 volts to 6.25 volts at less than 2mA, making it ideal for use in model avionics systems.

As state before this project uses two of the chips and they are supplied pre-programmed by me and marked "1" or "2" this signifies IC1 or IC2 and they must be fitted in the correct position for the unit to work.

Assembly

The unit only consists of 13 components so there is very little that can go wrong. The only 4 components that need to be fitted the correct way round are IC1, IC2, Q1 and D1. The correct orientation of these 4 components can be clearly seen in the component layout drawing.

The unit is housed in a small plastic box; the board is mounted in the box using servo mounting tape. This box can be fixed to the side or back of the Futaba TX with Velcro.

The main components IC1, IC2 used in this design are CMOS devices and can be damaged by static electricity. When handling these items it is advisable to take some basic precautions, do not wear clothing which builds up a static charge, or handle the item until needed and before you touch it, try to touch a water pipe which should earth any static charge you have built up. DO NOT connect yourself directly to the mains earth.

The different connections that you need to make to the board are shown in the table, this is to allow for the unit to be used with a Futaba or JR transmitter as the master.

Construction

The unit is very simple in design and so is fairly easy to build. Cut the veroboard to size first and check it is a good fit in the case, you will need too cut two corners off of the board too get it to fit. Then cut the copper tracks in the positions shown in the drawing of the track side of the board. Now you can fit the components making sure to fit the two wire links. Also make sure that you link across the tracks on the trackside of the board, this is best done with a blob of solder. Once completed the board should be fitted into the case, and the cables connected too the vero pins used for JP1-JP5 as per the connections table.

Always fit the unit to the back of the Futaba transmitter as this is supplying the power to the unit and it is best if this lead is kept as short as possible.

Futaba Master / JR Slave

Radio	JP1	JP2	JP3	JP4	JP5	LK1
Futaba		Pin 1		Sleeve	Pin 3	Fitted
JR	Tip		Sleeve

JR Master / Futaba Slave

Radio	JP1	JP2	JP3	JP4	JP5	LK1
Futaba	Pin 2	Pin 1	Sleeve			Not Fitted
JR				Sleeve	Tip

In Use

In operation the unit is used just as a Futaba or JR buddy box lead would be used, with the instructor using the master transmitter and enabling the students transmitter with the training switch on the master transmitter.

The only slight difference is that normally you would leave the students transmitter switched off so that it does not transmit a signal, the action of plugging in the buddy box lead powers the students transmitter partially. With this unit as it is powered from the Futaba transmitter if the Futaba is being used as the slave then it must be switched on, to stop it transmitting a signal the crystal or TX module should be removed. It is also best to switch on the Futaba transmitter before the JR.

Return to main page...