Subject:
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RCX IR Transceiver Circuit
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Thu, 23 Dec 2004 21:01:23 GMT
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Viewed:
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5662 times
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In lugnet.robotics, Ralph Toepper wrote:
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in lugnet.robotics Mark Bellis wrote:
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Would anyone be interested if I put my diagrams online, or has someone beaten
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i would like to encourage you to publish your knowlegde, as there is - as far,
as i know - no other source of information about that subject in the internet
today. So, you would be the first!
I am very interested in seeing your diagrams.
Greetings
Ralph
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I managed to get this one drawn today:
N.B. I cannot guarantee accuracy as this is my own interpretation of the circuit
of my own IR Transceiver, using data from reference books and tracing the
circuit myself, so I might have made mistakes. If you spot one, do let me know.
Explaining how it works will take some time and a considerable amount of text!
The dotted box bottom left is the serial port plug.
The transistors and diode pairs are in 3-pin surface mount packages. The 6Cp
transistor, being a higher power device, is in a larger package than the others.
I wasn’t sure if this was a MOSFET rather than a BJT. The range switch is on the
right - contact made for long range, open for short range. IC2 with the 33k and
100k resistors, capacitor and variable resistor form the oscillator that applies
the carrier wave to the transmitted signal. The variable resistor in my
transceiver had an in-circuit value of 11.6k ohms.
It looks like signals received from the PC on the RxD input are used to modulate
the +5V supply rail and they are then returned on TxD. If the PC pulls CTS low
then TxD will also go low. These return mechanisms allow the PC to detect the
presence of the IR tower.
The LED stays on after transmission finishes, due to the time taken for the 10uF
capacitor to discharge through it. I can’t remember if it was possible to see a
5.1V rating on the zener diode, but the voltage is indicated by te LED resistor
value of 470 ohms - that’s a normal value to use with a 5V rail.
In long range mode, assuming 2V drop per IR LED and 0.2V C-E saturation voltage
of the 6Cp transistor, there’s 4.8V across a 5.6 ohm resistor, giving 857mA
current - this is quite a lot to draw from a PP3 battery.
There seems to be a residual current through the IR LEDs of 4.4mA via the 6Cp
transistor B-E junction (0.6V drop). Therefore remove the battery if you’re not
using the tower for a while.
PLMKWYT. I won’t be able to draw any others till the new year, but this should
give us plenty to discuss till then.
Mark
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Message has 1 Reply:
 | | Re: RCX IR Transceiver Circuit
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| (...) Thanks for this one, Mark! For the sake of completeness, some data on devices used. Note: as there are "collisions" in SMD device names, these are only "very probable"... 1Kp: (URL) 3Kp: (URL) are NPN and PNP general purpose transistor. A4p: (...) (20 years ago, 28-Dec-04, to lugnet.robotics.rcx, FTX)
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Message is in Reply To:
| | Re: RCX IR Transceiver and Sensor Port Circuits
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| (...) i would like to encourage you to publish your knowlegde, as there is - as far, as i know - no other source of information about that subject in the internet today. So, you would be the first! I am very interested in seeing your diagrams. (...) (20 years ago, 18-Dec-04, to lugnet.robotics)
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