Model Radio
Control Electronics
Click the clock for
The Norcim website is a non-commercial,
educational site for electronics enthusiasts with an interest in Model Radio
Control. This first
page contains technical information covering the 
The inclusion of any material on
this site is completely free. Should you have any product or company or model shop or club activity
you wish to get exposure on the Norcim website or have any related ideas or
text you wish to be included, simply contact us by clicking the button below.
The link uses simple email so you can easily sort your text, photos, drawings
or circuits and attach them before sending….Where else can you get advertising
for your R/C interest, exposed on an established web site, completely free, no
strings attached??
The
information on this site is somewhat scattered but new stuff tends to be added
to the ‘Whatsnew’ page available from the link in the box a little way down
this page on the right. If it does not get there then it will be placed on a
page that’s most content related.
You will also find some special Google
‘content related’ adverts on all pages All of these are of interest to readers
of this site….simply click on the advert text of interest to go directly to
that site….note, if you see
arrows on the bottom left corner of the Google Add….click for more content related websites by
Google !!
I hope you enjoy the ramblings of the Norcim
Web Site and please do, come back soon!……. We are only ever a click away!
Much of the first page of the norcim
site involves coverage and fault finding of the
Micron
receiver faultfinding notes and general information
‘Radio
Control Model World’ Magazine projects at GCSE and A level
Micron
transmitter faultfinding and general information
Dual Conversion Fet
receiver Details and circuitry explained of
Micron’s Fet7 PPM FM receiver!
SLM
(Model) Engineers Surplus Stock from a
control horn to a forty-foot long precision lathe!!
norcim
2 More 40 MHz Tx/Rx notes plus a PCM system and a speed controller
plus Tony’s Website of R/C circuits and gadgets. Not to be missed!
norcim 3 A new page with Tx circuitry, an electric
glider design, an input from George Beeler at the NASA research center USA,
ramblings about receiver installation and a Multi channel Failsafe.
norcim
4 a
new page for the norcim site with some simple circuits of R/C interest.
norcim 5 commercial receiver testing by Radio
Guru Dave McQue UK.RCC
norcim 6 historical info on PPM radio control systems including
original Mathers/Spreng system
norcim
7 some original model aircraft design
from Nicholas Ingle plus some vintage stuff (page
construction)
Tony’s Website loads of R/C gadgets
and circuits with assembly notes! A real must for like-minded R/C
electronics enthusiasts.
Other Real Interesting Websites! Click for a host of like-minded R/C enthusiast sites.
Condensed speed controllers! John Chamber’s latest electric flight project. See Terry’s radio
notes2 above.
Note that a Norcim 8 page is on
the go.......It’s stepping stones…. (see the link at the bottom of this
page!)
Micron
Receiver Fault Finding Notes
General If assembled correctly; all four
receivers in the micron range should perform correctly at switch-on. There is
little or no variation between range (sensitivity) and other characteristics of
correctly assembled versions of the same type. (It is even difficult or
impossible to pick out a ‘good one’ to keep for 
yourself).
The FET receiver generally will show slightly more range
to complete loss of signal compared to the other versions, (probably
owing to increased front end stage gain.)
For receivers
that don’t work on completion of assembly. These often have a built in mistake and rarely suffer from a faulty
component. Look for 4k7 and 47K
resistors in wrong places as reds and org colours are similar in artificial
light. Also people get 4K7 mixed 
with 270K as they are the same three colours but opposite way round.
Coils that have been cut wrong and mounted the
wrong way round. IF coils that have had the
centre pin cut too short as the winding loops around this pin and if cut too
short will cut the winding. (Check primary pins for continuity using low ohms
on meter)
Sometimes capacitors get mixed up and you may find a 47p and a 47uf in the wrong places or similar.
Have a sample PCB to hand or do a ‘pencil rubbing’ of the boards before
construction, as it is possible for customers to join two small copper lands
with solder so that it looks correct as one land. (Particularly mini Rx)
Look carefully at the 104 caps, either the yellow type or the blue type as after soldering, the leg can
become detached from the side of the capacitor, shown by a crack around the
outside edge of the cap. This fault only occurs if the capacitors have been
mounted very close to the board where the thermal shock of soldering is
increased. If in doubt another 104 cap
can be touched to the bottom of the PCB, across the suspect cap, during test to
see if the problem clears.
Look for the obvious, as many
times, IC’s are put in the wrong boards or the wrong way round. Check that only
Futaba, Fleet, Multiplex, JR, or GWS, receiver crystals are being used in the
receiver.
Check that only the transmitter manufacturers crystal is being
used in the transmitter. (use of a different make of Xtal will almost certainly
result in an ‘off frequency’ transmission.
The decoders of the receivers rarely produce problems providing component values are
correct. Very, very rarely a
significant static shock (type that stings your finger when closing the car
door) can knock out the Cmos chip and this is shown by scope input readings to
the chip (normally clock @ 4volts & reset ramp of around 3 volts) being
clamped at below 1 volt. Indicating that the chip inputs have gone low
impedance and the chip needs replacing.
Often customers use flux on the
boards when soldering which unfortunately has an acid content and therefore
adds many unwanted resistors to the circuit. This condition can be detected visually
with residue on the boards. The only
possible cure is to clean the residue from both boards using a toothbrush
soaked in methylated spirits but often the flux has impregnated the board and
satisfactory operation cannot be regained and the receiver is not
recoverable. Replacement is the only answer.
Receivers that work but show low range this mostly points to the antenna input bits. Happily there are few of these parts
involved. (The 159 coil, the 27p capacitor, the antenna input cap and the
capacitor feeding pin16 input of the 3361 chip. Often the flex antenna can be
shorted to ground with a solder whisker on the PCB or a stray wire from the
flex antenna remaining on the board surface and touching the metal coil cover.
When cleared with a model knife, normal range is restored. Perhaps the wrong capacitor has been inserted
across the 159 coil. Is the coil the
correct way round? If the 159 coil
responds to tuning, then the lack of range could be further on in the circuit.
If the front end is checked out and OK then a possible lack of range could be found in the filter section of
the receiver. ‘The filter section’ has
its input from pin3 of the 3361… filters the 10KHz spot frequency…feeding it
back into the 3361 pin 5. The filters
involved vary with the receiver type. The standard and Comp receiver use a
transistor between the filters with associated resistors/capacitor. The filters rarely go wrong but the
transistor can be inserted with its legs wrong and associated resistor values
need checking. The transistor gives
around 10/12dB gain when fitted correctly. If you have an oscilloscope, the
following can be checked. With the Tx on the bench, with about 25 cm of aerial,
pin 3 or the base of the transistor will show around 0.1 volt of mixer output. If
the transistor is working OK then there will be 1/1.5 volts of IF at its
collector. (as seen on the scope). It is worth mentioning that the 3361 works
well without this extra gain as in the mini receiver.
However the amp is also used to increase white noise of the whole
circuit so that with the transmitter switched off, there is a pile of noise
activity at pin9, which bombards the 4015 decoder to keep its servo
outputs quiet. Note: - the mini receiver works differently and without
the IF amp there is a much reduced noise level at its 3361 pin9. This lower
noise helps to keep the 4017 decoder servo outputs quiet when the Tx is
switched off.
Voltage levels around the circuit.
I must admit that I do not have
any record of voltage levels. I often made sure that the receiver board was
getting 4volts supply from the decoder board (or slightly more,) but beyond
that always used the scope to prod around during faultfinding.
Remember that after trying
to get a receiver with a fault working, the coils could be well out of correct
setting. This does not matter for the 159-antenna coil, as the receiver will
still work at close range at any possible setting of this coil.
The setting of the IF coil however is critical to a quarter of a turn to
get any response at all from the servos. Resetting visually as compared with a
working receiver or a new replacement coil is a useful start.
The ‘Transmitter Power Meter’ kit available from micron is sensitive enough to detect the
oscillation of a receiver Xtal stage if its antenna is held very close to
the crystal. Also but not so convenient maybe, a spectrum analyser will pick up
the receiver crystal stage by simply holding the input probe close to the Xtal.
Mild jittering or servo noise using the Micron FET
receiver.
Although range and general performance of early dual conversion micron
receivers seemed OK, reports from some parts of the
RCMW magazine electronics projects
There has been several electronic
construction projects published in ‘Radio Control Model World’ magazine
over the last couple of years. These projects mainly used a copper strip board
(or ‘Veroboard’ to quote the manufacturers name). This was probably
intentional; as each project could easily be used at GCSE/A level electronics
course level, without the need for special printed circuit boards.
Veroboard is excellent for construction of
prototypes or one-offs but great care is necessary in preparing the
board to begin with to have the correct number of holes and to cut the copper
strips where shown on the drawing, before construction begins. It is also
necessary to carefully inspect and clean the edges of the board to make sure
the copper strips are not shorting together at the ends where the board has
been saw cut to size.
The adhesion of the copper strips to the
underside of strip board is not as good as a conventional printed circuit
board! Component placement should be
checked very carefully before soldering, as any necessary de-soldering often
lifts and breaks the copper strip. Copper strip repairs are difficult and
messy.
To help with correct component
positioning it is well worth spending some time with the board and drawing,
carefully marking each used hole with a felt tip pen. Any mistakes can be
cleared with an eraser. Component placement into marked holes is so much
easier.
Of the six projects that I completed, only one (the servo
tester) refused to work as the result of incorrect information in the
magazine. This was quickly covered in
the next issue with apologies. (The designer had listed the wrong transistor
type number! Oops). As soon as the correct 10 pence transistor was replaced,
the tester burst into life and has worked ever since.
Incidentally the correct transistor for
the Servo Tester should be ‘BC184L’.
Of the projects that used ‘off the shelf’
plastic boxes, I found that quite a bit of time was necessary, drilling and
preparing the box. This is particularly true of the ‘Transmitter Output Tester’
but if this stage is not rushed, the end result looks good.
Fault finding on the smaller projects like the ‘Lost
Model Alarm’ is restricted to a careful visual inspection of correct component
positioning, correct component values and correct preparation of the copper
strips. If no fault can be found, then because of the compact nature, the only
way forward would be to replace the board and components.
It is important to use the listed
component values and the exact type of components listed in the ‘Fast
NiCad Charger’ as component leakage current is important with this type of
‘voltage peak detect’ circuit.
All of the ‘Mini electronics projects
for the modeller’ (based on several of each project being assembled) if assembled correctly as per drawing,
with the correct components, will work at switch-on. Even the ‘Transmitter
Output Tester’ (the most complex project in the series) works at switch-on, its
single coil adjustment only maximises its sensitivity to give full reading at
10 metres.
In the unlikely event of the finished
unit not working, look for the obvious assembly mistakes as outlined in the
Micron receiver fault finding notes above.
Re: the Transmitter Output Tester I have found that it can be tuned (as
assembled to drawing) to test the output of 40MHz transmitters also. The coil
setting is about one turn further in, clockwise (from the 35MHz setting). The
unit can even be set to test 72MHz transmitters for the
‘Toko’ do make a special coil for 72MHz
type 499GNS0056R. I have not tried this but it should be suitable. It has its
own internal capacitor so again the 22p in the circuit should be left out.
There is talk of a possible 51MHz R/C band here in the
Some recent testing suggested the use of
unusually small value capacitors for suppression of electric motors. This
suggestion was based on the results of using a synthesised RF signal generator
and lots of capacitor values! The test looked at the capacitor value and length
of leg forming a natural tune circuit. Using the test results, two capacitors
of value 4700pf and 5mm leg length were fitted from each motor terminal to its
metal case with a 3300pf across the motor terminals. These values apply to the 
As a check a spectrum analyser probe was
held close to the motor during operation and the attenuation of the 35MHz
content could clearly be seen. Several hundred motors using these capacitor
values have been sold now and there have been no reports of motor interference,
even with the receiver mounted within 10mm of the motor rear cover! A practical way to check for motor
interference is to range check with the transmitter antenna fully collapsed
without the motor running, then do the same check with the motor running. If
there is less than 10% difference in range, then all is well.
Electric flight motors cont’d. It is worth remembering that the ‘Transmitter Output Tester kit’ listed from Micron has an optional
flylead input that can be directly clipped to a motor brush terminal to measure
the motor interference! I found that this worked well on the bench but some
care is necessary if using the Tx to operate the motor, as the tester also
wants to pick up the transmitter output! Once you are aware of this, it’s
simply a matter of keeping the transmitter a couple of metres away with fully
collapsed antenna.
MICRON Transmitter fault find/general
notes
The very first ‘Micron’ transmitter circuitry that I assembled was
actually fitted into a ‘redundant’ commercial transmitter case and sticks. The
transmitter had developed a fault that was not repairable but the hardware was
still excellent including sticks, switches, meter, antenna etc. Some ingenuity
was necessary to secure the two Micron printed circuit boards in place but the
end result made an excellent transmitter working on the 35MHz band!
Transmitter electronics kits are still
available from Micron now as far as I am aware and are still assembled on two printed
boards (this was done to suit the original Micron case). The seven-channel circuitry changed in recent
years owing to the obsolescence of the dedicated ‘Motorola’ R/C coder chip. The replacement coder is interchangeable with
the earlier type and now uses ‘bog-standard’ easy to get electronic parts,
which are readily available from most hobby electronics shops.
There is little point in commenting on
the earlier circuitry as inevitably most problems involved the special IC,
which is now unobtainable. The only practical remedy for repair of these is
replacement with the later version coder board.
Having assembled several of the later
coder boards and seen other peoples efforts, the faults found were as follows:
-
Blown 4017 IC. This is usually caused by incorrect battery wiring giving a reverse
input voltage! The other circuitry survives but it is worth replacing the 22uF.
Usually a new 4017 solves the problem but the battery wiring must be checked
before switching on again.
Note that the coder circuit will run without the IC plugged in at
around 1 KHz which can be seen at the yellow output wire on a scope, or even
heard using a crystal earpiece. This test shows that most of the circuit is
functioning except the IC. If there is no life, check component position, in
particular the correct positioning of the transistor legs into the board.
Working but a channel(s) is missing this fault can often be traced to an
incorrect setting of one of the joystick pots. All the stick pots must be
pre-set so that their wiper is at mid position, when the sticks and in-flight
trims are at a centre position. This can be checked using a multimeter.
It is also possible that one of the
crimped connectors of the plug-in flylead from the stick, has not located
correctly in the plastic shell and as a result, the crimp has pushed out of the
top of the shell. Relocating the crimp, making sure that the small plastic
fingers of the shell are pushed in to secure the crimp, is usually a cure.
Another possibility is a blown diode (usually
caused by accidental shorting of the board to the edge of the metal case,
during testing and adjustment). Often this can be 
confirmed using a multimeter on low Ohms
setting across each diode in turn (there are 10 of them!), to find the ‘odd one
out’, followed by replacement.
Coder board quality, I have seen more than one coder Printed
board now which was not up to the usual crisp copper etch that is normally
seen. On these boards it was necessary to carefully inspect the copper lands
and cut through with a model knife, the several bits that not intended to be
joined! So look carefully with light behind the board.
The Transmit Section is a smaller board that feeds the
antenna and like the coder board, if assembled correctly, does function at
switch-on. The outputs of this board has been passed by the ERA (Electrical
Research Association) for
Not working at all this points to resistors or capacitors
in the wrong places. Remember if you find one wrong then there will be another
where that one should have been! Look for coils that have had the wrong pins
snipped. These will need replacement. Check the transistor legs are going into
the correct holes on the board. Check that only Micron or Futaba crystals are
being used and ‘Tx’ is indicated on the crystal tab. Try another crystal in
case the one fitted is duff.
Reverse Polarity fault. This always shows itself as a burned
brown/black 100R resistor in front of the output transistor. Unfortunately both
the output transistor and RFC will need replacing. The oscillator coil always
survives, as does all of the other circuitry.
John Keeling from down under (Neighbours country) sent a message
recently asking for Micron circuits to be included in the web page. Without doubt
this would be of considerable help to customers with some technical knowledge,
particularly if like John, they live so far away! Thanks John for your kind
comments and also for suggesting looking at www.rc-soar.com!!!!! Some good stuff there!
Humble thanks to Michael Shellim who must have taken considerable time and
effort to do the write-up of the Micron mini receiver and Nigel Wrigley for his
input. First time I’ve seen it, so honest, there was no collusion! Many thanks to Mr Shellim.
I thought of kicking off with some
technical notes about the Micron FET receiver, to be perfectly honest, this is the
only Micron receiver that I have an up to date circuit for! The use of a FET
(field effect transistor) in the front end of a radio control receiver is not
new. Many years ago now, probably late 60’s, ‘Mike Dorffler’ of the excellent
American ‘R/C MODELLER MAGAZINE’, produced a wonderful self-build receiver
design using a JFET in the front end! The Micron JFET front end is not too
different from this early pioneers design. The fundamental advantages of this
type of front end are acknowledged in the RSGB 
‘Radio Communications Handbook’, 5.16.
As a result, the Micron receiver does handle strong out of band transmissions
particularly well. (Aluminium Scarecrow Antenna Interference).
Microns use of the FET is interesting in
that some of the known disadvantages of this device have been addressed.
JFET’s, used in mixer stages, do like, a
high oscillator drive to work well. Unfortunately JFET’s also have poor
isolation of the oscillator frequency and this results in the oscillator
frequency being transmitted via the receiver antenna! Although this
transmission could still be termed as ‘flea-power’; Just imagine thousands of
such receivers on a good flying day, all transmitting on a frequency that has
nothing to do with radio controlled model aircraft! The interference to other
users of the radio spectrum would be at risk and it is important that R/C
receiver emission is kept to an absolute minimum.
The Micron FET receiver uses dual
conversion 
input. The resulting bleed through of
the oscillator to the antenna is in the order of a couple of nanowatts and
considered insignificant.
Mike Dorffler’s pioneering use of this
front end was limited to the single conversion crystals of the period.
Unfortunately with the receiver crystal only 455KHz away from the incoming
frequency, most of the oscillator power found it easy to squirt from the
receiver flex antenna!
Another problem with JFETs was the
divergence of characteristics from 
one device to another but technology has
advanced and JFET characteristics are now much more controlled, with even
selected versions of the same device available.
The Micron FET receiver circuit diagram comes next and surprisingly, its almost
as simple as the Mini receiver that they do, except for the two transistors
added on at the front! I will try and run through the circuit as best as I can
without causing too much pain for the reader!
The 35MHz parent transmitter signal is
picked up by the 85cm flex antenna. (Length is not critical). This excites L1,
producing a 35MHz signal input to the BF244A (gate). The 27p/4.7uH trap grounds
the 13.5MHz image frequency and the 24.3MHz oscillator leak through via the 15p
cap. Meanwhile the 24.3MHz plug-in crystal oscillator circuit output is
injected via the 0.1 cap to the BF244A source terminal and mixing of the two
frequencies occurs, producing a 10.7MHz output at the BF244A output. There are
several other frequencies produced by mixing but the 10.7MHz crystal filter
rejects these.
The selected 10.7MHz signal is passed on
to pin 16 of the Motorola 3361 chip. Mixing takes place for the second time
using the on-board 10.245MHz Xtal oscillator. This produces a 455KHz signal at
pin 3.
This signal is filtered by the 10KHz
filter (CFU455HT) and then amplified in the chip, with the FM content being
detected at pin 9.
The 4k7 and .022 cap at pin 9 get rid of
white noise on the output signal, leaving rounded signal pulses (from the
transmitter) of about 0.5v peak to peak. Note L2 needs adjusting to achieve this.
Pin 12 is an input to a squaring amp with outputs at pins 13 & 14. These
two outputs (4v pp) are used to clock the standard Cmos counter chip, giving up
to 8 servo outputs. The 2N3904 provides an extremely servo noise free supply of
around 4volts to the whole receiver. The ‘image frequency’ rejection of this
receiver is around 60dB which means that transmitted signals on
the 13.6MHz band (image band) would have
to be a million times stronger to cause a significant interference problem.
This compares with ‘normal’ single conversion receiver image rejection figures
of around 10dB, allowing 34MHz band signals to cause havoc when only 11 times
stronger! The 34MHz band is for ‘Ministry of Defence’ use and has been little
(if any) used over recent years.
Following the events of September 11 in the
it is possible we could now see increased activity on
the 34 MHz band by the Ministry of Defence in the
The following thoughts are written on
the assumption of the above: -
1. Don’t fly close to any known M.O.D.
establishment.
2. If the flying site is close to
an M.O.D. establishment and unusual glitches are experienced, then try an
alternative 35 MHz frequency channel. (The interference is mathematically
derived and may not be on another channel).
3. Replacing the ‘single conversion
receiver’ with a ‘dual conversion’ type (plus special Rx crystal) will
completely eliminate the problem.
4. www.ukrcc.org will be the quickest site to report any
problems of this nature, associated with the above.
5. Remember that the above is only a
possibility, so don’t try to fix it if you don’t experience a problem!
SLM (MODEL) ENGINEERS are now the
Note! To return to my site (which
obviously you will want to do!) use the ‘back arrow’.
James Ramsey sent the following notes of interesting magazine projects:
-
My main interest is R/C scale model boats but I have come
across three items that may be of more general interest.
1) R/C meter, details in E P E magazine, Apr1998, this meter
costs about £42 for bits etc., will determine frequency of 27 35 40 and other
MHz transmitters. Great for checking xtals (inc. RX by putting in TX) and if Tx
is transmitting correct frequency. For AM only it will detect no of channels
mark spacing, and also check output from an RX and finally is a servo tester!
2) Digiserv, which adds ten, ‘on – off’ switches to any channel
but still retains main use. (E P E Oct 1998.) This works on 27 AM, but
needs an addition to work on 35/40 FM. Anyone interested contact me.
3) Noise trap, simple two-component gadget to fit in long servo
leads to remove picked up interference. Could send more details if interested.
James is happy to advise on the above projects via Email to James
Ramsey
E P E magazine is the
R/C Electronic gadgets 2 Further interesting electronic projects which have been
published are as follows: -
1) Sealed Lead Acid
2) 12v
Both of the above projects will find use for model
boat drive batteries and aircraft starter
3) Sound Record/playback unit EPE Apr 99. Can record
20sec of sound/speech and play back either once or looped. Sound is stored in
digital form on chip and can be recovered even after battery switched off. Good
one for sound effects on scale model boats.
A Hot Tip!
If you use one of the cycle pump type
de-soldering tools, try pushing a short length of silicone fuel tubing on to
the nozzle end so that just a couple of millimetres protrudes from the tip. The
resulting ‘soft end’ seals around the solder joint better as the tool is used
and also reduces the recoil kick back. The silicone tube is also unaffected by
the solder iron heat!
Useful web sites: -
www.micronradiocontrol.co.uk kits for R/C receivers, speed controllers, servos,
chargers, etc.
www.modelflying.co.uk ‘Radio Control Models & Electronics’ one
of the leading UK R/C model aircraft magazines.
www.rcmodelworld.com ‘Radio Control Model World’ one of the
leading
www.epemag.wimborne.co.uk ‘Everyday Electronics’ a leading
www.flyingsites.co.uk general information regarding radio control
model aircraft.
The UK Radio Control Council the Radio Control technical advisory council
to the Govt ‘OFCOM’.