LARCing around.... (DIY Lexicon LArc?)

Got hold of a 224xl a short while back. going to start playing around with it soon.
However, we don't have a LARC.

Been flicking through the service manuals etc to see what they are all about.
From what I can see they are just spitting out some data across the rs232 serial buss.
This makes me think that it wouldnt be too difficult to come up with a replacement made using an arduino. I know that LARCs seem to be think on the ground, so moving towards the future could be great to have some replacement system in place..

Anyone know more about the language they speak?

I guess we're going to have to get one and stick a serial monitor on it and try and figure out what its doing.

If anyone has any ideas on its implentation and wants to chime in with some ideas this would be an interesting subject to discuss I think.

I think we'd have to call it 'LARD"

Nice idea - and perhaps it could be used by the Lexicon 300 & 480L owners out there?

I think Lexicon had a switcher to go between multiple units but I am sure a more elegant solution should be arranged

Nick Froome

Yeah that would be great. I really dont think it would be all that difficult to accomplish.
But right now I dont know exactly what information it is that the larc spits out (and receives).
I've ascertained so far that the larc was built around intels first ever microcontroller. the 8749

This was a cpu, clock, ram and rom combined into one chip. the rom was a UV erasable eprom, and so probably wouldnt be hard to extract the code from. although it would probably be easier to start that from scratch if using a more modern microcontroller such as an arduino etc.

I see we stuck here If anyone did do anything on this case, i would ike to participate or help.....so to not start from begining over again. i just finished servicing from 224XL and one is without larc, so doinfg some small controller would be greate, rather than downgrading unit to 4.4 firmawere and using old blue control, which is easy to clone as is only multiplex and demultiplex reading of buttons/slider.

Been thinking about this for a while, I have already done remotes for the AMS RMX and DMX, just need to sit down and work out the protocols.

bradholland said:

Yeah that would be great. I really dont think it would be all that difficult to accomplish.
But right now I dont know exactly what information it is that the larc spits out (and receives).
I've ascertained so far that the larc was built around intels first ever microcontroller. the 8749

This was a cpu, clock, ram and rom combined into one chip. the rom was a UV erasable eprom, and so probably wouldnt be hard to extract the code from. although it would probably be easier to start that from scratch if using a more modern microcontroller such as an arduino etc.

Click to expand...

If the interface between the LARC and the brains is RS232, the only thing standing in your way is finding the protocol.

For my monitor controller, I used an RS232 interface between the main control box and the wired remote.  There is a Silicon Labs C8051F314 microcontroller and MAX3221 level shifter in both units.  Power for the wired remote comes through the RS232 cable, too. The micro in the remote scans buttons and an encoder and controls various LEDs. It is the "master" in that it sends commands to the micro in the main unit, which receives those commands and decides how to set the volume controls and the switches.

As for using an Arduino, remember that for this project, you'll end up spinning a PCB, so why restrict yourself to making it fit as a shield?

And, as usual, the most difficult part of this project will be making a suitable enclosure.

Its actually RS422.

radardoug said:

Its actually RS422.

Click to expand...

So it's still a UART, just with differential transmit and receive lines. (RS485 would be half duplex with some control for who talks.) I assume that the cable assembly has twisted pairs for the signal lines?

Yes, it is RS422, but that doesn't matter as is just voltage level.....protocol is thing to figure out, since there is no written in any of lexicon documents.

On serial interface pcb where RS422 driver is, there is also option port (but connector itself is not soldered on  any of 224xl) and on pin 8 of U1, which is also passed to option connector you can have both communication (from lex to larc, and from larc to lex) depending on setting of W1 and W3 jumpers. So there i can steal signal and take it to com port of pc, since i do not have log analyzer and to check what is going on. Will try that later.....

As for pcb and enclosure......hardest thing is to make sample of code working from some arduino shield to lex, rest is a game to do

Another thing for XL is to "downgrade" it to X, by using 8.1 software (which was highest version of 224X) and to use either blue controll or made one, as it is just mupltiplex, demultiplex reader of bottuns and led's, which is directly read/controlled by 224 SBC.....also, except adding rom's with 8.1 firmware, there are some jumpers which needs to be set, along with parallel port driver ic on sbc (most right connector on sbc pcb from fron side, serial is most left one).

Just playing with it......it's working, one thing, 224 is expecting "48" i hex format offcourse to be sent to it, before it starts power up diagnostic......

marinbnm said:

On serial interface pcb where RS422 driver is, there is also option port (but connector itself is not soldered on  any of 224xl) and on pin 8 of U1, which is also passed to option connector you can have both communication (from lex to larc, and from larc to lex) depending on setting of W1 and W3 jumpers. So there i can steal signal and take it to com port of pc, since i do not have log analyzer and to check what is going on. Will try that later.....

Click to expand...

I used to have PC-based COM port spy software. It displayed and allowed you to save to a file whatever came over the wire.

wouldn't it be smarter to use a PC based USB-Serial port and get a GUI (with recall) written?

Rochey said:

wouldn't it be smarter to use a PC based USB-Serial port and get a GUI (with recall) written?

Click to expand...

This requires having a PC connected to the thing, and someone writing PC software.  Which is fine, as this is likely to be used in a studio that has a DAW.

My monitor controller design splits the difference. It has a real RS-232 port on the front. You can plug it into a computer that has a COM port (I use a USB-to-serial dongle on my Mac) to connect to it so you can drive it from the computer, or you can plug in a hardware control box.

It's best to use genue RS232, i tried to use many usb to rs232 converters with varous machines and mosty of the time i had problems.......

I mainly will develop hardawar larc clone, first new pc's don't have com port and adapters are no realiable, as stated before specialy when 224 use RS422 whih have even higher voltage levels than RS232.
And another, hardware is more "real thing" than to stare at pc, as many users i talked would like to have.

marinbnm said:

I mainly will develop hardawar larc clone, first new pc's don't have com port and adapters are no realiable, as stated before specialy when 224 use RS422 whih have even higher voltage levels than RS232.

Click to expand...

RS-232 levels are +3 to +15 for space and -15 to -3 for mark. RS-422 is basically TTL output levels differentially driven, so an output will be be at least 2.5 V and up to the +5 V rail (assuming the canonical AM26LS31 driver). RS-422 receivers do have a wide input voltage range because there is the expectation of ground differentials over a 1,000-meter cable run.

I've seen 224XL Larcs going between 150-500 EUR on ebay this week. Maybe not necessary to DIY one yourself?

Those are the older parallel ones. Only work on the 224 and 224X. Not the 224XL (L for LARC)

I have an old LARC lying around. Came from a dead 224 and is not in the very best shape. But if one is interested: Give me a sign!
Chris

Is it plastic or metal?

Eh? It's plastic - I've never ever seen a LARC made of metal. Have you?