Download
dsc.zip, Zip file containing images and txt files.
Download
dsc.zip, Zip file containing images and txt files.
Ordering parts or complete
kit
Introduction
When you are installing your RC equipment in your latest model, if you follow the equipment manufactures instructions you will be aware of the problems of having the TX aerial extended and possibly breaking or bending it, also the rate at which the TX batteries go flat. The TX batteries go flat this quickly because you have a crystal fitted and are radiating RF power, hence the need to have the aerial extended, if you could get around this situation then you would be able to operate the TX with the aerial down and hence not risk breaking it, and have much extended battery life as well.
This is the function of the direct servo controller, it is for use with standard PPM sets, not PCM sets which have this function anyway. The basic idea is that you can remove the crystal from your TX and leave the aerial retracted, plug the lead from the direct servo controller into the buddy box output of your TX and then replace the RX in the model with the direct servo controller, plugging the servos into it. The controller has been tested with both Futaba and JR equipment and the buddy box connections for this equipment are given, but it will work with all makes of equipment that have a buddy box output, that outputs a pulse stream from the encoder. This can been found by reading the manufactures instructions, if they say that you need both TX's switched on but only one crystal fitted or only one aerial extended (usually the instructor) then this is the system used by the DSC. If the instructions say that you have to have both aerials extended and crystals fitted to both TX's for the same radio channel, then the buddy box system used by this equipment is not compatible with the DSC. The DSC also will only decode the first eight channels from your transmitter, so if you have a set which has more than eight channels then these extra channels will be lost.
Technical Bit.
The DSC could have been designed around one of the CMOS shift register IC's as used in most receiver designs, but this would have had a few draw backs, the main one of which is that the DSC would only have worked with one polarity of input pulse. To overcome this problem it was decided to use a PIC16C54 micro-controller, the software in the PIC takes care of the incoming polarity and adjusts for it. With this design a normal or inverted pulse train can be fed into the DSC and it will decode the pulses to give separate outputs for each servo.
The PIC16C54
The micro computer used in the mixer is a PIC16C54 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 12 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.
Assembly
The unit only consists of 9 components, so there is very little that can go wrong. The only two components that need to be fitted the correct way round are IC1 and Q1. The correct orientation of these two components can be clearly seen in the component layout drawing. The DSC unit can be made to work with any type of airborne equipment and to this end there are two links on the PCB that need to be set for the type of equipment you wish it to work with, these links are shown on the component layout drawing. These links provide for the reversal of the +5v and 0v lines on the servo connectors and the battery connector. Warning. If you set these links incorrectly and plug in the receiver battery you will destroy IC1.
The unit is housed in the receiver case that was used for the old RCM&E FM system, this case is still available and the details for how to obtain this item are given in the parts list. The main component IC1 used in this design is a CMOS device and can be damaged by static electricity. When handling this item 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 lead that you need to connect the DSC to your transmitter is shown in the accompanying drawings, I have only been able to test the unit with Futaba and JR equipment and so these are the only makes of equipment that I have shown connection details for. Testing Operation Testing is very straight forward connect the DSC unit to the buddy box output and switch the Transmitter on ( remembering to remove the crystal or TX module ), and then connect a receiver battery pack to the left most connector (you can use any of the output connectors if you wish) on the DSC. Plug a servo into the first output channel, this servo should respond to movements of the relevant stick on the transmitter, repeat this test for the rest of the channels on your transmitter, just as you would with a receiver.
And Finally
I hope that this direct servo controller is of use to those of you who do not have a computer Radio set that has this functions built in, and that you have gained an insight into the possible uses of the PIC range of micro computer chips in the world of model avionics. If anyone is inspired into trying to develop PIC based projects for themselves then please don't hesitate to write to me for advice or information about this wonderful little chip.
