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RADIO CONTROL BY BOB YOUNG Multi-channel radio control transmitter; Pt.7 This month, we deal with the final system alignment and the programming instructions for the Mk.22 transmitter. This is mainly a matter of deciding the features you want and connecting the various wander leads. To begin it will be necessary to re-read the May, June and July 1996 issues of SILICON CHIP in which the basic instructions for the alignment of the RF module and the encoder are discussed. As we left the project in the July issue, the transmitter was completely assembled and working up to the point of radiating a modulated signal albeit not correctly tuned. Before we go any further, make sure your batteries are fully charged before you start. Charging is accomplished using a power supply set at 60mA or a dedicated plugpack charger. These are available at any good model shop however you will need to change the connectors. The charge plug must be a non-shorting 2.5mm jack type and is inserted into the socket located on the lower front right of the Tx. The tip of the charge plug is wired positive. Remove all micro-shunts and leads from the encoder and RF modules. It is probably best to begin proceedings with the adjust­ment of the expanded scale voltmeter circuitry as this will give a good indication of the state of your batteries during the alignment process. Trimpots VR16 and VR17 on the encoder PC board control the set points and range of the meter. VR17 sets the low point (+8.8V) and VR16 controls the range (sensitivity). To adjust the meter, hook up a variable voltage source to the encoder GND and +9.8V pins on TB7. Set both trimpots to their midpoints, set the power supply to +8.8V and switch on power. Set the meter pointer to “0” using VR17. Now increase the voltage to +10.8V and set the pointer to “10” using VR16. Drop the volts back to +8.8V and reset VR17. Continue this cycle until the meter reads “10” at +10.8V and Fig.1: the ideal modulated waveform and “0” at +8.8V. recommended rise times. 72  Silicon Chip With this setting, the meter will peg immediately after charging and drop back very quickly to less than “10” as the surface charge is dissipated. As nicads are considered exhausted at 1.1V per cell, the meter will give an excellent indication of the state of charge of your batteries. Stop flying at “0” as you will have only about 10-15 minutes of safe flying after this. Slip the Tx power input socket back onto TB7 (PWR) and fire up your spectrum analyser (yes, as I have stated before, you will need an analyser) and plug in the power connector to the RF module. Open the May 1996 issue of SILICON CHIP and work your way through the tuning sequence presented in that issue. The produc­tion antenna ended up at 1.3 metres instead of 1.5 metres long but the tuning range will accommodate that change. The only area needing special attention is the final shape of the modulated waveform. Fig.1 shows the ideal waveform and recommended rise Fig.2: an overview of the encoder layout showing the major pro­gramming controls and plug groups. Notice that all eight input configurations are identical. times. It may be necessary to play with the value of R7 on the RF module, as mentioned previously, to adjust for the spread in the FETs. Once the RF module is properly tuned, seal the ferrite slugs with wax to prevent them moving. It is now possible to drive a receiver from the transmitter. As all input stages have been disabled, only the default waveform will be transmitted (all 1.5ms pulses). Switch on the receiver and plug a servo set to 1.5ms neutral (most modern servos) into channel 1. Better still, plug in a pulse width meter. Remove all leads and micro-shunts from the encoder PC board, switch on the trans­mitter and the pulse width meter should read 1.5ms or the servo move to neutral, if you have followed the instructions in the June 1996 issue. The 10kΩ 10-turn trimpot VR2 (NEUT) is there to provide neutral adjustment. Clockwise rotation increases the pulse width. Use this to set the neutral if it is not already correct and switch the Tx OFF. Try to get into the habit of changing the plugs and sockets with the Tx OFF. There are only one or two plugs that may cause problems and these are not usually moved once in place (power sockets). The Tx must be switched OFF when changing the RF module. The Mk.22 transmitter is now ready for business, so let us move on to the real work. Fig.3: each channel input has three main components: the VARY-NORMAL 3-pin header set, the CHANNEL INPUT 3-pin header set and an Adjustable Servo Travel Volume (ATV) potentiometer. (see Fig.2, page 80, July 1996 issue) which are free to wander anywhere on the PC board. All control elements are wired in an identical fashion with the centre lead carrying the signal and the two outside leads for positive and negative. All control inputs on the encoder are fitted with identical, mating 3-pin headers (plugs). Any control may be connected to any chan­nel in any order. This arrangement results in a transmitter of the utmost flexibility. Even the front panel controls can be programmed in the most suitable manner for the task at hand. Toggle switches can become retract switches, dual rate switches or mix IN-OUT switches. Sense of operation may be reversed, channel allocation changed or direction of the servo travel reversed very quickly and without complex menu stepping. Fig.2 gives an overview of the encoder layout showing the major programming controls and plug groups. Notice that all eight input configurations are identical so that it is only necessary to master one to have complete mastery over all eight or indeed 24 channels. Each channel input has three main components: the VARY-NORMAL 3-pin header set, the CHANNEL INPUT 3-pin header set and an Adjustable Servo Travel Volume (ATV) poten­t­iometer – see Fig.3. Each of the channel input sets are numbered on the PC board and run from left to right. These three items give rise to an almost limitless variety of programming options. We will work through some of these options, paying particular attention to the basic principles involved, in order to build a good knowledge of how the system works. This will make the more com­plex programming tasks (such as CROW) much easier to understand when we describe them in coming issues. Programming the encoder The Mk.22 encoder utilises what is perhaps best defined as “Wander Lead” programming. All controls are wired with identical 3-pin sockets Fig.4: this diagram shows how the various micro-shunts (shorting links) must be placed across TB10, if the configuration module is not used. August 1996  73 We will begin with the simplest and most fundamental tasks and work forward from there. Load the appropriate micro-shunts and sockets as we go through the programming sequence. Configuration module The configuration module is not used in the basic Mk.22 transmitter. This was briefly mentioned and pictured in the June 1996 issue. If the module is not plugged into the configuration port TB10, then micro-shunts (shorting links) must be placed across TB10 as shown in Fig.4 to complete these open circuit input leads (see circuit in the March 1996 issue). These micro-shunts also play an important role in the mixing programming and we will deal with that later. Channel allocation As a result of the wander lead concept, channel allocation is a matter of deciding which controls should utilise which channel and plugging the 3-pin sockets onto the appropriate CHANNEL INPUT header pins. Channel allocation is a most important function when we come to such complex programming options as CROW, changing stick modes or matching a Mk.22 Tx to another brand of radio. As glitches tend to affect channel 1 more than any other channel, it is best to keep the flying controls away from channel 1. The standard Silvertone channel allocation is as follows: Channel 1 Allocation motor 2 aileron 3 elevator 4 rudder 5 gear 6 flaps 7 aux 1 8 aux 2 Other brands of R/C equipment use different channel alloca­tions. To match a Mk.22 Tx to a model already fitted with another brand of receiver, it is a simple matter to duplicate the channel allocation by rearranging the order of the sockets. Servo reversing Servo reversing is simply a matter of rotating the 3-pin socket on any 74  Silicon Chip and we will now move on to some of the more advanced features. End point adjustment Fig.5: the sense of operation on the toggle switch for dual rate operation can be reversed by reversing the 3-pin socket on the VARY-NORMAL header. Adjusting throttle linkages can be a tricky business as it is often almost impossible to get both ends exactly right. Using the ATV in conjunction with adjustable linkages overcomes this problem. Whilst not a true end point adjustment it certainly will adjust both end points simultaneously and will set the exact amount of servo travel needed to match the carburettor arm trav­el. Fig.6: use this diagram when pro­ gramming toggle switch operation. Dual rate programming of the CONTROL INPUT headers by 180°. Keep in mind that any error from absolute neutral will be doubled. For example, if the throttle servo is at one end before reversing, then it will immediately fly to the other end when reversed. If the trim is at absolute neutral when the socket is reversed, then no servo movement will be apparent. Programming servo travel In order to simplify the programming, certain configura­tions call for the ATV (adjustable servo travel volume) poten­tiometer to be connected to become a completely different type of volume control. The VARY-NORMAL header pin sets provide this function. When a micro-shunt is placed on the centre/left pair of pins as in Fig.5(a), the CHANNEL GAIN potentiometer is programmed as the ATV potentiometer. In this mode, servo travel may be ad­justed from 20-120% (0.9 - 2.1ms) of the normal servo travel using the channel gain (ATV) poten­tiometer. Clockwise rotation increases the amount of servo travel. If the micro-shunt is placed on the centre/right pair of header pins, as in Fig.5(b), then the ATV pot is allocated to other functions and the servo travel reverts to the NORMAL non-adjustable 100% level (1 - 2ms) and the ATV potentiometer is no longer available for servo travel adjustment. At this point the transmitter should have all of the micro-shunts loaded on TB10, the main controls hooked to the CHANNEL INPUT headers and the micro-shunts loaded on the VARY-NORMAL headers. You can now move multiple servos simultaneously. This completes the basic programming All 24 channels may be programmed for DUAL RATE operation. Simply remove the micro-shunt from the VARY-NORMAL headers on the channels intended for DUAL RATE operation and connect the desired toggle switches to the appropriate headers. Any of the front panel toggles can be used on any channel. The choice should be based on convenience of operation. Sense of operation of the toggle switch can again be re­versed by simply reversing the 3-pin socket on the VARY-NORMAL header – see Fig.5. When the toggle is in the VARY position the ATV potentiometer becomes the DUAL RATE set pot. Thus with the switch in the NORMAL location, the ATV pot is disabled and a non-adjustable 100% servo travel is available. With the switch in the VARY position, the ATV pot is used to set the amount of DUAL RATE variation. It is usual to select the VARY position with the toggle DOWN. The amount of DUAL RATE adjustment ranges from 20% to 120%. Anticlockwise rotation decreases the amount of servo travel. Note that it is possible to program the Mk.22 Tx for increased throw in the DUAL RATE setting. Toggle switch programming There are two identical toggle switch modules built into the main encoder PC board module. These are located on the righthand side of the PC board just above the righthand input groups (see Fig.2) These modules consist of two 3-pin headers and a potentio­ meter. Fig.6 shows these in detail. Note that the lefthand 3-pin header of each toggle module is labelled SW and this Kit Availability Kits for the Mk.22 transmitter are available in several differ­ent forms, as follows: Fully assembled transmitter module......................................................$125.00 Basic transmitter kit (less crystal)............................................................$89.00 Transmitter PC board...............................................................................$29.50 Crystal (29MHz).........................................................................................$8.50 Fully assembled encoder module..........................................................$159.00 Encoder kit.............................................................................................$110.00 Encoder PC board...................................................................................$29.50 Transmitter case kit................................................................................$395.00 Full transmitter kit (includes all the above).............................................$594.00 Post and packing of the above kits is $3.00. Payment may be made by Bank­­­card, cheque or money order to Silvertone Electronics, PO Box 580, Riverwood, NSW 2210. Phone (02) 533 3517. will receive the 3-pin socket from the toggle switch (see Fig.2c, July 1996 issue). Thus, any toggle switch on the Tx front panel may be used as the actuator for the toggle channels. The righthand 3-pin header labelled CH is the output connection. The short jump­er cable with a 3-pin socket at each end (see Fig.2e, July 1996 issue) is connected to this header. The other end of this patch cord can go to any CHANNEL INPUT header in your channel alloca­tion plan. Thus any two channels may be allocated to toggle switch actuation. Servo reversing is available simply by reversing the CHAN­NEL INPUT socket as normal. A novel feature is the ability to very quickly reverse the sense of operation of the toggle switch by simply reversing the socket on the SW header. Thus UP-ON becomes DOWN-ON. With the channel input programmed for NORMAL mode, adjust­ ing the toggle module potentiometer will provide from almost zero to 100% travel volume. Clockwise increases the servo travel. Another novel feature of this arrangement is that 180° of servo travel is easily obtained by using the toggle module poten­tiometer in conjunction with the VARY mode ATV pot. Some care is needed here in case the brand of servo you are using has its rotation angle limited by internal stops to less than 180°. Check to ensure that the servo is not straining against the internal end stops. There is provision for two toggle modules on the standard encoder PC board. Programming knob control The standard Mk.22 case is punched for four toggle switches and two knob controls. The knob control consists of a panel-mount potentiometer upon which are mounted limiting resistors and a cable fitted with a 3-pin socket (see Fig.2d, July 1996). The resistors allow the full 270° of rotation to be used without driving the channel beyond the electronic limits allowable. Thus, the knob control is a completely self-contained proportional control element which may be treated as one axis of a 2-axis stick assembly. It may be allocated and reversed in the normal manner. There are two knob controls in the standard Mk.22 transmit­ter, however all eight channels could easily be knob controls in a suitable case. Programming slide control A slide control unit is available as an option and again may be considered a single axis proportional control ele­ ment. It may be allocated and reversed as normal. However, this would require a slot to be cut in the case by hand. A slide control suitable for flaps is available as an optional extra. That is all that space allows for this month. Next month we will discuss mixing, dual control and frequency SC interlock. Scan Audio Pty Ltd August 1996  75