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Why are lego rcx sets so cheap.

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So I am trying to find some pieces related to another topic I made and look at the rcx sets for fun and see the prices. They were so cheap! I found one that sold for about 100 dollars that was in good condition. If you also wanna see them you can search rcx on bricklink.

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Perhaps because they are outdated and hard to use on modern computers?

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Shhhhhh!!!

Man - keep it low. RCX' are one miracle - particularly when you flash the RobotC (or other free operating systems/firmwares). So we keep this to ourselves and all is good :pir-sweet:

Spoiler

I believe this is because they don't run on Java/Script or Python or the like. Also, it is a bit of fiddling to get the software/s running on a Win10 machine or equivalent on Macs. LEGO does not support them anymore. The 9V system is gone for more than a decade. 9V cables need a little maintenance when they are aging. In other words: This is a ton of fun!!! Well for me that is. I have about 10 of them. Plus a couple of Scouts and Spybots - all programmed with Bricxcc ... they are beautiful)

Best
Thorsten

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5 minutes ago, Toastie said:

Shhhhhh!!!

Man - keep it low. RCX' are one miracle - particularly when you flash the RobotC (or other free operating systems/firmwares). So we keep this to ourselves and all is good :pir-sweet:

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I believe this is because they don't run on Java/Script or Python or the like. Also, it is a bit of fiddling to get the software/s running on a Win10 machine or equivalent on Macs. LEGO does not support them anymore. The 9V system is gone for more than a decade. 9V cables need a little maintenance when they are aging. In other words: This is a ton of fun!!! Well for me that is. I have about 10 of them. Plus a couple of Scouts and Spybots - all programmed with Bricxcc ... they are beautiful)

Best
Thorsten

Yeah I know the feeling because I have(sadly had) a friend who has more than 10 of them. It's so cool when he controlled like 5 of them at the same time.

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Because there isn't really much market demand for them?  They do require more effort and skill to get working.

 

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1 hour ago, Jim said:

Perhaps because they are outdated and hard to use on modern computers?

Hehe ... yes they are: 23 years and counting. But so are LEGO bricks. They have been around since more than 60 years - and we still don't buy the more recent Chinese bricks! :pir-grin:

But hard to use on modern computers? Hmmm:

Win10 64bit: Get the Bricxcc software. Get a USB to serial adapter. Plug it in. Run device manager, click on connections (LPT&COM), find the USB to serial adapter, assign it to a COM port < 9 if it is not already, otherwise Bricxcc won't find it. Get a serial LEGO IR tower, probably from a BL site which also sells the RCX'. Turn on the RCX, startup Bricxcc, do an auto search for an RCX or RCX2 brick (depending on your firmware). Done. :pir-huzzah2:

Or get RobotC for the RCX. Get the firmware for the RCX. Startup RobotC. Turn the RCX on. Download the RobotC firmware to the RCX. Done. :pir-huzzah2:

OK, now comes the thing: Programming at this point is Not Quite C which a bit of C or Robot C which is even more so C.

And yes, it is much less of a hassle when using the LEGO serial tower with a USB to serial adapter than using the LEGO USB tower, which, although it looks like it should - it doesn't.

Summary: It is a bit annoying. But I would not call it too hard, is it? 

Best
Thorsten

 

 

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Is there a way to emulate the serial or USB IR tower using a microcontroller + IR LED?

 

 

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@Toastie That isn't so bad indeed! I always read horror stories about the need for virtual machines etc. But this isn't so bad.

@dr_spock obviously has the right answer. The answer that is always right. Things are cheap when they are in low demand (compared to the availability).

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8 hours ago, Tcm0 said:

Yes, that one works. Well it is even far "easier" for those who still like soldering irons: All you need is a 38kHz modulated IR diode and one of the 3pin 38 kHz IR receivers (there are so many, I use the TSOP 34838 - runs on 3.3V, is smaller than TSOP1738 and very reliable - and dead cheap). That's basically it. For the 38kHz on/off modulation you may use an Arduino (then you can also use the remaining computing power to fly to the moon); a CMOS/TTL NAND (as they use in the tower) oscillator works nicely as well, or use the smallest 6 or 8 pin PIC from the microchip line (or any other vendor). All you need to do is convert the signal on the TX line of the serial port to 38kHz IR light - and detect 38kHz light on the RX line.

Bit protocol is a bit odd: 2400 baud, 1 start-, 8 data-, 1 stop-bit, odd parity.

Here is some more and nicely organized background info (just in case).

http://www.johnholbrook.us/RCX_guide.html

http://www.mralligator.com/rcx/

Also: Get a USB to serial converter that provides full hardware control pinout; the IR tower itself does not do >anything< of that sort but simply bridges pin 8 (RTS) and 7 (CTS) of the serial port. Some LEGO and other software looks for that signal to detect whether the tower is present; it is a bit frustrating when looking at the circuit diagram of the tower you find no hint of flow control at all, but the thing you made yourself seems not to work simply because that bridge is not there - or your USB converter cannot imagine that some folks still do hardware handshake stuff.

Here is all you need plus a couple of hardware examples:

http://www.mientki.ruhosting.nl/data_www/lego_knex/lego_electronica/ir_tower/ir_tower.html

Have fun!
Best
Thorsten

P.S.: Just forgot: Yes, the IR detector picks up the IR light from the diode because there is no flow control at all. LEGO called it "echo" back in the days. When you want to be very smart (as I wanted to be) and electronically block that echo, some LEGO software does not work anymore, as this "echo" tells the program "a properly working tower is connected".

Edited by Toastie

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Dear Old Soldering Iron Enthusiasts (OSIEs),

I just digged out my RCX IR tower, opened the documents and checked twice - just to make sure that I did not write stupid things coming just from memory.

It appears as if all is OK so far in my previous post. Just to round things off - here are a couple of more things (none of which are essential):

  • You can operate the LEGO IR serial tower with just three lines: RXD, TXD, GND when using e.g. a terminal program like HTerm to check things out or run your own programs off from an Arduino or the like.
  • Sending bytes to the tower triggers the internal mono-flop, which in turn awakens the TSOP1738 IR receiver, as you can see in Marc Bellis' circuit diagram shown here: http://www.mientki.ruhosting.nl/data_www/lego_knex/lego_electronica/ir_tower/ir_tower.html
  • As long as the LED on the tower is on, you can monitor incoming data from the tower. After that time it goes to bed again and nothing comes through. Now, sending e.g. CR or LF or Null repeatedly every 3 seconds or so to the tower keeps it alive, and you can continuously monitor the IR traffic in the room.
  • All this does not apply for your home-brew IR serial devices, which can be as simple as IR LED + 38 kHz modulator and TSOPXXX38 as receiver.
  • LEGO software sometimes wants to see the RTS CTS bridge but that does not do anything to the serial traffic protocol.
  • And finally: The original serial cable that came with the RIS1.0 set flips RXD and TXD. To get a RS232 plug into the tower you need to use a rather "slim" plug. Always in for something special, these TLG engineers :pir-huzzah2: 

Best
Thorsten

Edited by Toastie

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On 2/15/2021 at 6:30 PM, Toastie said:

I just digged out my RCX IR tower, opened the documents and checked twice - just to make sure that I did not write stupid things coming just from memory.

Hello,

An corrected schematic diagram can be found here : http://www.robotika.sk/mains.php?page=/projects/lego/tower/index.php

Google-Translate help to read Czech Description

 

Jo

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Good evening Jo,

wow, what a nice find!!! This makes things much clearer!!! Thanks a million. The diagram is to the point. This is the new reference then.

Best wishes,
Thorsten

BTW: Found a really cool code (IMHO) for generating 38kHz on an Arduino (works well on Uno R3 clone, pin 11):

void setup() {
 pinMode (3, OUTPUT);                // Just to switch ON/OFF
 pinMode (11, OUTPUT);               // Pin 11: Timer 2 "A" output: OC2A 
 // set up Timer 2
 TCCR2A = _BV (COM2A0) | _BV(WGM21); // CTC, toggle OC2A on Compare Match
 TCCR2B = _BV (CS20);                // No prescaler
 OCR2A =  208;                       // Original value: 209. 
                                     // Original comment: "compare A register value (210 * clock speed)
                                     //  = 13.125 nS , so frequency is 1 / (2 * 13.125) = 38095"
                                     // This results in 37.83 kHz on the Uno R3 clone board
                                     // Changed to 208 - this results in 38.01 kHz
}  // end of setup

Copied from: https://forum.arduino.cc/index.php?topic=102430.0

I hooked-up an IR LED (or just plain vis LED) with cathode to pin 3, anode via 1kOhm to pin 11. Running the sketch on pin 11 38kHz/50% duty cycle is always present. Pin 3 is just to turn the LED on/off.
Using any of the SoftSerial libraries allows you to modulate the Baud rate on the LED 38kHz emission. The thing is: That code does not interfere with any of your loop code.

Best
Thorsten 

Edited by Toastie

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