Re: radio controlled toy
- From: ehsjr <ehsjr@xxxxxxxxxxxxxxxxx>
- Date: Tue, 15 Dec 2009 19:55:42 -0500
Steven Cooke wrote:
----- Original Message -----
From: "Steven Cooke" <cookeei@xxxxxxxxxxx>
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¤t
=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
Your 1702 transistor might be an ED1702. See the datasheet:
http://www.datasheetcatalog.com/datasheets_pdf/E/D/1/7/ED1702L.shtml
Looking at the pins, the pinout is:
**
| E *
| B *
| C *
**
Review the schematic drawn below to make sure it matches
what you have. You didn't label the transistor with ebc, so
be sure I've drawn it correctly. The component you identified
as "red covered component" is undoubtedly an inductor - I
identified it as L1 on the schematic below. I wasn't sure
if one of the resistors was 3K7 or 5K7 so check that value,
and change the schematic as needed.
View in Courier font:
V+ ---+
|
o
/
o
|
+-----+--[L1]--+------+-----+-------+
| | | | | |
| [10K] [Xtal] | [30pF] [100pF]
| | | /c | |
[10nF] +--------+----| | +-----[L2]---Antenna
| | \e | |
| [5K7] | [100R] [50pF]
| | | | |
Gnd---+-----+---------------+-----+-------+
Re: the measurements. You indicated you weren't sure which was
collector, emitter and base. Look at the pinout on the datasheet
and you can repost the measurements with any possible guesswork
eliminated, and specify the value for Vcc
Ed
.
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