radio controlled toy

transmitter:


http://s297.photobucket.com/albums/mm226/donquay_bucket/?action=view&current

I have been able to work out what most of the components are except for a
red component in the transmitter and a green component in the reciever. I
do
not know the orientations of any of the transistors in the schematic (but
I
can guess) and where to get the information for them such as the 1702L
PM20
on the transmitter. I do not know the function of the 30pF capacitors
across

I have been able to work out what most of the components are except for a
red component in the transmitter and a green component in the reciever.

What I think is the base of the transistor (1702L PM20) has 1.4V when read
with my multimeter and 1.8V when read with the oscilloscope probe (1Mohm
input resistance). What I think is the emitter of the resistor measures
1.71V with my multimeter but has an unusual shaped wave 1.16V(p-p) measured
with the CRO.

What I presume is the collector has a 9.09MHz 8Vp-p sine wave (I presume
that the oscilloscope probe is affecting it in some way - the probe has a
capacitance of 23pF).

page 26-30 Information on the size of the antenna

page 674 - The pierce oscillator (seems to have an extra capacitor in
series to the crystal)

page 179 - succests that a capacitor across the emitter and capacitor
acts as a feedback capacitor (in this example a non-crystal oscillator)

My problem is in understanding what is happening in the circuit. I expect
there to be a 0.6V drop across the base-emitter junction.

Is this circuit
running is class D or something?

It doesn't look like it is biased as such.
Has anyone in this newsgroup built a pierce oscillator or worked with one?

I have an Advanced Diploma of Electronics and a Bachelor of Science, but it
is times like these I feel I shouldn't have been awarded either of them.

Once again, I would appreciate any insight that could be given to my
project.

I am attempting to replicate some of the functions of a radio control car
with my own electronics so I have reverse engineered a toy that I bought at
a shop. It seems to be the simplest type that I can find. The car moves
forward when the button is pressed the first time and then in a circle when
pressed the second time. The motion in a circle is achieved mechanically so
the direction of the motor is all that changes.

The transmitter appears to just be an on/off signal for 27.145MHz. I do not
know how the receiver selectively receives this signal.

receiver:

http://s297.photobucket.com/albums/mm226/donquay_bucket/?action=view&....
=circuit001.jpg

transmitter:

http://s297.photobucket.com/albums/mm226/donquay_bucket/?action=view&....
=circuit002.jpg

I am quite comfortable with my understanding of most of the functions on the
reciever to do with the motor (H-bridge) and the siren and LEDs.

I have been able to work out what most of the components are except for a
red component in the transmitter and a green component in the reciever. I do
not know the orientations of any of the transistors in the schematic (but I
can guess) and where to get the information for them such as the 1702L PM20
on the transmitter. I do not know the function of the 30pF capacitors across
some of the transistors but I think it might have to do with the miller
effect. In fact I have quite a bit of difficulty understanding why a lot of
the capacitors and inductors are in the circuit. There is a transformer in
the reciever circuit which isn't even connected to anything. I think that
most of the schematics are understandable, but I could be wrong.

I would appreciate any insight that could be given to my project.

Thankyou,

Steven Cooke

----- Original Message -----
From: "Steven Cooke" <cookeei_at_adam.com.au
Newsgroups: sci.electronics.design
Sent: Sunday, December 06, 2009 9:44 PM
Subject: radio controlled toy



transmitter:



http://s297.photobucket.com/albums/mm226/donquay_bucket/?action=view&current
=circuit002.jpg

I have been able to work out what most of the components are except for a
red component in the transmitter and a green component in the reciever. I

do

not know the orientations of any of the transistors in the schematic (but

I

can guess) and where to get the information for them such as the 1702L

PM20

on the transmitter. I do not know the function of the 30pF capacitors

across

Progress report:

I bought an oscilloscope and measured some of the voltages at different
points in the transmitter circuit.

What I think is the base of the transistor (1702L PM20) has 1.4V when read
with my multimeter and 1.8V when read with the oscilloscope probe (1Mohm
input resistance). What I think is the emitter of the resistor measures
1.71V with my multimeter but has an unusual shaped wave 1.16V(p-p) measured
with the CRO.

(a bit like a chair if this can be read after transmission)
/\_ /\_
\/ \/

The bottom of the graph is at 1.5VDC and the top is at about 2.66VDC. It has
a frequency of about 27MHz.

What I presume is the collector has a 9.09MHz 8Vp-p sine wave (I presume
that the oscilloscope probe is affecting it in some way - the probe has a
capacitance of 23pF). I then measured after the decoupling 100pF capacitor
and read a 27MHz signal of 2Vp-p and after the 23 turn winding as a 0.25Vp-p
signal.

I have looked at a few books in my attempt to understand the transistor, the
transmission line and the antenna of this circuit.

Reyner, J.H. (1942) Modern Radio Communication - Volume II (3rd Edition),
Pitman Publishing Corporation, New York

page 26-30 Information on the size of the antenna

Boylestad, Robert L., Nashelsky, Louis (1982) Electronic Devices and Circuit
Theory, Prentice/Hall International editions

page 674 - The pierce oscillator (seems to have an extra capacitor in
series to the crystal)

Hibberd, R. G. (1973) Transistor Pocket Book, Butterworth & Co., London

page 179 - succests that a capacitor across the emitter and capacitor
acts as a feedback capacitor (in this example a non-crystal oscillator)

My next step is to attempt to replace this transmitter with one I build
myself, to replace components with easily accessable components.

My problem is in understanding what is happening in the circuit. I expect
there to be a 0.6V drop across the base-emitter junction. Is this circuit
running is class D or something? It doesn't look like it is biased as such.
Has anyone in this newsgroup built a pierce oscillator or worked with one?

I have an Advanced Diploma of Electronics and a Bachelor of Science, but it
is times like these I feel I shouldn't have been awarded either of them.

Once again, I would appreciate any insight that could be given to my
project.

Thankyou,

Steven Cooke

http://www.youtube.com/user/cookesteven30

***

I originally posted this a month ago but I don't think it got onto the
newsgroup. I will post it again because I am preparing to make a new post.

***

Thankyou to everyone who has responded to my post. I appreciate that a
little bit of feedback makes a task seem less daunting . I am going to
go and buy the parts and try to construct a replacement transmitter. I
will let you know how well it goes.

(Current ASCII Schematic) View in Courier font:

V+ ---+ 6VDC **
| | E *
o | B *
/ | C *
o **
|
+-----+--[L1]--+------+-----+-------+
| | | | | |
| [10K] [Xtal] | [30pF] [100pF]
| | | /c | |
[10nF] +--------+----| | +-----[L2]---Antenna
| | \e | |
| | | | |
| | +-----+ |
| | | |
| [5K1] [100R] [50pF]
| | | |
Gnd---+-----+---------------------+-------+

L1 is possibly an inductor (RF Choke) or a combination inductor capacitor.
L2 is a set of windings to decrease the size of the antenna. Xtal is set
at 27.145MHz

+------+------+----+-----+-------+-+--------+
| |PD_at_25C|VCEO|IC |Hfe |@|IC(cont)|
+------+------+----+-----+-------+-+--------+
|ED1702|625mW |25V |500mA|132-189|@|100mA | Original
+------+------+----+-----+-------+-+--------+
|BC338 |625mW |30V |800mA|100-630|@|100mA | Proposed Replacement
+------+------+----+-----+-------+-+--------+

JK> Do you have a picture of the PCB itself somewhere?

Very difficult to get a picture that isn't blurry with my current
equipment.

JK> I'd trust the scope over the meter.

I think I have been using it wrong . I'll make the readings again and
resubmit.

JK> Wes Hayward (1994-2000) "Introduction to Radio Frequency Design" 3rd
Printing, American Radio Relay League
JK> www.northcountryradio.com/PDFs/column007.pdf
JAL> "Three-transistor Toy CB Walkie-Talkie"
JAL> single-transistor superregenerative detector
JAL> Thomas H. Lee (2004) "The Design of CMOS Radio-Frequency Integrated
Circuits, 2nd Edition, Cambridge University

Homework

JAL> Neither link works as posted. Try these instead:

receiver:
http://s297.photobucket.com/albums/mm226/donquay_bucket/circuit001.jpg

transmitter:
http://s297.photobucket.com/albums/mm226/donquay_bucket/circuit002.jpg

My apologies for posting incorrect links.

Steven Cooke

http://www.youtube.com/user/cookesteven30

"Steven Cooke" <cookesteven30_at_hotmail.com> wrote in message news:...

3rd try to send this...

***

I originally posted this a month ago but I don't think it got onto the
newsgroup. I will post it again because I am preparing to make a new
post.

***

***

The following is a transcript of the audio that appears in my video on
youtube
http://www.youtube.com/watch?v=BSqDVACew3g

The video contains a reasonable summary of the stage I am up to on my
project. It is taking quite a long time. The video is about 60MB if one
intends
to download it. I have tried to understand the circuit but I am still
unable.
Any input would be appreciated.

***

I am attempting to replicate some of the functions of a radio control car
using electronic components which are locally available.

This car seems to be the simplest type that I can find. The car moves
forward when the button is pressed the first time and then in a circle
when
pressed the second time. The motion in a circle is achieved mechanically
so
the direction of the motor is all that changes.

I have reverse engineered this toy. First I disassembled the car and the
transmitter and copied the copper track side of the boards onto pieces of
paper. I flipped over the board and worked out the positions of the
components in relation to the tracks, recording the values of the
components wherever possible.

Upon consultation with people from the sci.electronics.design newsgroup,
I made the assumption that the transistor which is labelled 1702L PM20 was
a Philips ED1702L after obtaining the datasheet.
http://www.datasheetcatalog.com/datasheets_pdf/E/D/1/7/ED1702L.shtml

The transmitter and receiver circuit both work on 6V input so I soldered
voltage regulators to the circuits which were able to be connected to
plugpacks. I later bought a variable power supply for easier
experimentation. I bought an oscilloscope to study the signal and voltage
levels at different parts of the transmitter circuit. I also used
multimeters to measure DC voltages.

I could not identify a red component in the transmitter. I assumed that it
was an inductor based on class A power amplifiers that I have seen which
use an inductor in the collector output stage to create a voltage swing
centered around the value of the DC supply voltage. The component could
also
be an inductor/capacitor combination as is present in tank circuits to
select
a required frequency. In order to measure an inductance I needed an
inductance measuring device. I bought a multimeter that had such a
function
but it did not have a low enough setting to measure this inductance. I
found
a circuit that purported to measure values between 3 microhenries and 7
milli
henries in the ARRL handbook for the radio amateur. It may also be found
at
www.armory.com/~rstevew/Public/TestEquip/IndMeterAdapter.htm. I
constructed
this circuit on some stripboard and despite my use of ceramic capacitors
rather than monolithic capacitors as stated, the circuit did not seem to
work
as advertised. The circuit oscillates and then passes created signals
through
a 74HC132 integrated circuit until a signal may be read by a digital
voltmeter.

Instead I bought a kit from Altronics that was able to measure inductance
easily. I desoldered the red component and soldered some longer leads to
enable the connection to the connection posts on the meter. The meter gave
a
value of 2.56 microhenries for the inductor.

The final component that required description was a ferrite cored inductor
near the antenna. The dimensions that I measured (using a ruler with
millimeter gradings) were a radius of 4mm and a coil length of 5.5mm.
There
were 24 and three quarter turns of enamelled copper wire. Using a version
of Wheeler's formula that I found on the internet
L=(0.394*r^2*n^2)/(9r+10b)
microHenries (where r is radius, n is number of turns and b is length of
the
coil), I found the inductance to be 4.244 microHenries. Perhaps I should
also
have used the altronics meter to confirm this result, but I haven't. I
bought
a ferrite core and plastic holder that have been discontinued from Dick
Smith
Electronics (Australia's answer to Radio Shack). This plastic holder was
thinner than the original so I performed calculations to try to match this
inductance with 0.125mm thickness enamelled copper wire. I settled on 35.5
winds after performing the necessary algebra and spreadsheet calculations.
I
created the winding by using a glue gun to hold the wire in place then I
wrapped some sticky tape around the windings.

Original

V+ ---+ 6VDC **
| | E *
o | B *
/ | C *
o **
|
+-----+--[L1]--+------+-----+-------+
| | | | | |
| [10K] [Xtal] | [30pF] [100pF]
| | | /c | |
[10nF] +--------+----| | +-----[L2]---Antenna
| | \e | |
| | | | |
| | +-----+ |
| | | |
| [5K1] [100R] [50pF]
| | | |
Gnd---+-----+---------------------+-------+

L1 is 2.56 microHenrys. L2 is a set of windings to decrease the size of
the
antenna 24.75 windings. Xtal is set at 27.145MHz

Altered

V+ ---+ 6VDC **
| | C *
o | B *
/ | E *
o **
|
+-----+--[L1]--+------+-----+-------+
| | | | | |
| [10K] [Xtal] | [33pF] [120pF]
| | | /c | |
[10nF] +--------+----| | +-----[L2]---Antenna
| | \e | |
| | | | |
| | +-----+ |
| | | |
| [5K1] [100R] [56pF]
| | | |
Gnd---+-----+---------------------+-------+

I was unable to find exact matches for the capacitors so I altered them to
be higher than the original values. I replaced the 2.56 microHenry red
component with a fixed value 2.2 microHenry inductor. I created an antenna
similar to the one on the original toy by wrapping some 0.9mm picture
hanging
wire around a coathanger wire until 20cm length was achieved.

I tried to find a similar transistor from a list within the catalogue
based
on the maximum power dissipation, the maximum voltage across the collector
emitter, maximum collector current and similar Hfe. I decided that the
BC338 had the closest values for each of these.

+------+------+----+-----+-------+-+--------+
| |PD_at_25C|VCEO|IC |Hfe |@|IC(cont)|
+------+------+----+-----+-------+-+--------+
|ED1702|625mW |25V |500mA|132-189|@|100mA | Original
+------+------+----+-----+-------+-+--------+
|BC338 |625mW |30V |800mA|100-630|@|100mA | Replacement
+------+------+----+-----+-------+-+--------+

Understanding the circuit operation is difficult. I tried to find a
similar
circuit with a good description in the literature. For a time I believed
the
circuit to be a pierce oscillator minus the capacitor in the feedback
path.
Oscillators are classed by the connection of the feedback network at the
output and the way the feedback network is connected to the input. In
order
to understand the circuit I need to know where the input is coming from
and
where the output is. It seems to me that the output is at the collector,
where the crystal sits providing a kick to the circuit. The 30pF capacitor
directs the output to the input at the emitter.

I have measured the signals at both input and output and found that there
is a
phase shift. In an oscillator circuit there is supposed to be a total
phase shift
of 0. The gain also needs to be equal to 1 at this point. Because this
circuit has
input at the emitter and output at the collector, it should be a common
base
configuration, but I do not see a capacitor to ground the AC signal
attached
to the base.

Books about oscillators typically only describe the wien bridge,
phase-shift,
twin-T, Colpitts, Clapp, Hartley, Armstrong and then a few crystal
oscillators, none of which is similar to this.

I found some books from the Australian Department of Civil Aviation to be
enlightening but it suggests that there are practicals which may be
performed
of which I do not have a copy. Instead a book by Patrick and Fardo called
"Electricity and Electronics" provided a circuit I could use to measure
the
input and output characteristics of the transistor. I attempted this but I
think I may have had the transistor around the wrong way for some of the
tests. The notion in these books is that the transistor may be described
mathematically as a 4 terminal device. If I could describe the crystal
also,
perhaps I could understand how this circuit works.

Regardless of my lack of understanding I connected the circuit together,
turned it on and found that it was capable of changing the direction of
the
motor within the car. However something smells hot on the system and I am
reluctant to keep it turned on for very long in case something catches on
fire.
My next step is to work out what is getting hot (my thoughts are the
transistor
or the output inductor).

I have taken apart a few other radio controlled toys to see how similar
they are
to this toy. More elaborate toys have directional controls for the wheels
which
are controlled by a second motor. A walkie talkie also makes use of a
crystal
oscillator, but I have not studied these in depth yet.

I was unable to find copies in libraries of any of the books mentioned in
the
newsgroup sci.electronics.design. I found a book by an author of one of
these
books but it was not particularly well written so it has not persuaded me
to
buy the book sight unseen.

***

Steven Cooke
http://www.youtube.com/cookesteven30/

***

The following is a transcript of the audio that appears in my video on
youtube
http://www.youtube.com/watch?v=BSqDVACew3g

The video contains a reasonable summary of the stage I am up to on my
project. It is taking quite a long time. The video is about 60MB if one
intends
to download it. I have tried to understand the circuit but I am still
unable.
Any input would be appreciated.

***

I am attempting to replicate some of the functions of a radio control car
using electronic components which are locally available.

This car seems to be the simplest type that I can find. The car moves
forward when the button is pressed the first time and then in a circle
when
pressed the second time. The motion in a circle is achieved mechanically
so
the direction of the motor is all that changes.

I have reverse engineered this toy. First I disassembled the car and the
transmitter and copied the copper track side of the boards onto pieces of
paper. I flipped over the board and worked out the positions of the
components in relation to the tracks, recording the values of the
components wherever possible.

Upon consultation with people from the sci.electronics.design newsgroup,
I made the assumption that the transistor which is labelled 1702L PM20 was
a Philips ED1702L after obtaining the datasheet.
http://www.datasheetcatalog.com/datasheets_pdf/E/D/1/7/ED1702L.shtml

The transmitter and receiver circuit both work on 6V input so I soldered
voltage regulators to the circuits which were able to be connected to
plugpacks. I later bought a variable power supply for easier
experimentation. I bought an oscilloscope to study the signal and voltage
levels at different parts of the transmitter circuit. I also used
multimeters to measure DC voltages.

I could not identify a red component in the transmitter. I assumed that it
was an inductor based on class A power amplifiers that I have seen which
use an inductor in the collector output stage to create a voltage swing
centered around the value of the DC supply voltage. The component could
also
be an inductor/capacitor combination as is present in tank circuits to
select
a required frequency. In order to measure an inductance I needed an
inductance measuring device. I bought a multimeter that had such a
function
but it did not have a low enough setting to measure this inductance. I
found
a circuit that purported to measure values between 3 microhenries and 7
milli
henries in the ARRL handbook for the radio amateur. It may also be found
at
www.armory.com/~rstevew/Public/TestEquip/IndMeterAdapter.htm. I
constructed
this circuit on some stripboard and despite my use of ceramic capacitors
rather than monolithic capacitors as stated, the circuit did not seem to
work
as advertised. The circuit oscillates and then passes created signals
through
a 74HC132 integrated circuit until a signal may be read by a digital
voltmeter.

Instead I bought a kit from Altronics that was able to measure inductance
easily. I desoldered the red component and soldered some longer leads to
enable the connection to the connection posts on the meter. The meter gave
a
value of 2.56 microhenries for the inductor.

The final component that required description was a ferrite cored inductor
near the antenna. The dimensions that I measured (using a ruler with
millimeter gradings) were a radius of 4mm and a coil length of 5.5mm.
There
were 24 and three quarter turns of enamelled copper wire. Using a version
of Wheeler's formula that I found on the internet
L=(0.394*r^2*n^2)/(9r+10b)
microHenries (where r is radius, n is number of turns and b is length of
the
coil), I found the inductance to be 4.244 microHenries. Perhaps I should
also
have used the altronics meter to confirm this result, but I haven't. I
bought
a ferrite core and plastic holder that have been discontinued from Dick
Smith
Electronics (Australia's answer to Radio Shack). This plastic holder was
thinner than the original so I performed calculations to try to match this
inductance with 0.125mm thickness enamelled copper wire. I settled on 35.5
winds after performing the necessary algebra and spreadsheet calculations.
I
created the winding by using a glue gun to hold the wire in place then I
wrapped some sticky tape around the windings.

Original

V+ ---+ 6VDC **
| | E *
o | B *
/ | C *
o **
|
+-----+--[L1]--+------+-----+-------+
| | | | | |
| [10K] [Xtal] | [30pF] [100pF]
| | | /c | |
[10nF] +--------+----| | +-----[L2]---Antenna
| | \e | |
| | | | |
| | +-----+ |
| | | |
| [5K1] [100R] [50pF]
| | | |
Gnd---+-----+---------------------+-------+

L1 is 2.56 microHenrys. L2 is a set of windings to decrease the size of
the
antenna 24.75 windings. Xtal is set at 27.145MHz

Altered

V+ ---+ 6VDC **
| | C *
o | B *
/ | E *
o **
|
+-----+--[L1]--+------+-----+-------+
| | | | | |
| [10K] [Xtal] | [33pF] [120pF]
| | | /c | |
[10nF] +--------+----| | +-----[L2]---Antenna
| | \e | |
| | | | |
| | +-----+ |
| | | |
| [5K1] [100R] [56pF]
| | | |
Gnd---+-----+---------------------+-------+

I was unable to find exact matches for the capacitors so I altered them to
be higher than the original values. I replaced the 2.56 microHenry red
component with a fixed value 2.2 microHenry inductor. I created an antenna
similar to the one on the original toy by wrapping some 0.9mm picture
hanging
wire around a coathanger wire until 20cm length was achieved.

I tried to find a similar transistor from a list within the catalogue
based
on the maximum power dissipation, the maximum voltage across the collector
emitter, maximum collector current and similar Hfe. I decided that the
BC338 had the closest values for each of these.

+------+------+----+-----+-------+-+--------+
| |PD_at_25C|VCEO|IC |Hfe |@|IC(cont)|
+------+------+----+-----+-------+-+--------+
|ED1702|625mW |25V |500mA|132-189|@|100mA | Original
+------+------+----+-----+-------+-+--------+
|BC338 |625mW |30V |800mA|100-630|@|100mA | Replacement
+------+------+----+-----+-------+-+--------+

Understanding the circuit operation is difficult. I tried to find a
similar
circuit with a good description in the literature. For a time I believed
the
circuit to be a pierce oscillator minus the capacitor in the feedback
path.
Oscillators are classed by the connection of the feedback network at the
output and the way the feedback network is connected to the input. In
order
to understand the circuit I need to know where the input is coming from
and
where the output is. It seems to me that the output is at the collector,
where the crystal sits providing a kick to the circuit. The 30pF capacitor
directs the output to the input at the emitter.

I have measured the signals at both input and output and found that there
is a
phase shift. In an oscillator circuit there is supposed to be a total
phase shift
of 0. The gain also needs to be equal to 1 at this point. Because this
circuit has
input at the emitter and output at the collector, it should be a common
base
configuration, but I do not see a capacitor to ground the AC signal
attached
to the base.

Books about oscillators typically only describe the wien bridge,
phase-shift,
twin-T, Colpitts, Clapp, Hartley, Armstrong and then a few crystal
oscillators, none of which is similar to this.

I found some books from the Australian Department of Civil Aviation to be
enlightening but it suggests that there are practicals which may be
performed
of which I do not have a copy. Instead a book by Patrick and Fardo called
"Electricity and Electronics" provided a circuit I could use to measure
the
input and output characteristics of the transistor. I attempted this but I
think I may have had the transistor around the wrong way for some of the
tests. The notion in these books is that the transistor may be described
mathematically as a 4 terminal device. If I could describe the crystal
also,
perhaps I could understand how this circuit works.

Regardless of my lack of understanding I connected the circuit together,
turned it on and found that it was capable of changing the direction of
the
motor within the car. However something smells hot on the system and I am
reluctant to keep it turned on for very long in case something catches on
fire.
My next step is to work out what is getting hot (my thoughts are the
transistor
or the output inductor).

I have taken apart a few other radio controlled toys to see how similar
they are
to this toy. More elaborate toys have directional controls for the wheels
which
are controlled by a second motor. A walkie talkie also makes use of a
crystal
oscillator, but I have not studied these in depth yet.

I was unable to find copies in libraries of any of the books mentioned in
the
newsgroup sci.electronics.design. I found a book by an author of one of
these
books but it was not particularly well written so it has not persuaded me
to
buy the book sight unseen.

***

Steven Cooke
http://www.youtube.com/cookesteven30/

"Steven Cooke" <cookesteven30_at_hotmail.com> wrote in message news:...

3rd try to send this...