Text communication over 2 wires

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tblunt

New Member
Hi everyone.
Im brand new to picaxe and Ive been looking around over the last few days doing some research and I have a question for you all wise ones.

What i want to do:
I work in theatre in the auditorium with patrons very close to me. What i would like to do is make a silent com system consisting of 2 small lightweight portable boxes with a screen eg 40x2 or large LCD that can do large font & a keyboard and link them together and be able to type a message on one keyboard and have it display on the other boxes screen.

For a bit more complexity I want it to be able to make a beep in the receiving box & also control the back light so it is off until a message is received then turns on for a time then goes off again & I would like to be able to use the 'F' keys to print an often used word eg. pressing 'F1' '1' 'F2' = Mic 1 Not Working
Oh and the cable to link them together has to be 3 Pin Mic cable eg shield + 2 cores, the power doesnt have to be run on here I can have power supplies for both boxes.

Is this possible with a picaxe or do i need something else?
I know this will be a huge learning curve for me in programing something like this but if it will do what i want i am willing to put in the effort.


Thank you for your advice in advanced
Tom
 
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MartinM57

Moderator
But TB has the luxury of 3 wires so standard RS232 comms and an investment in some X1/X2 PICAXES that have serin timeouts would surely make the job pretty easy.

@TB - download the Programming Editor (free) and have a good read of manuals 1, 2 and 3, especially the KBIN (also the KEYLED command where it shows you how to wire up an (old-fashioned, not USB) keyboard) and SERIN commands

Everything you seem to require is very do-able, but overall reasonable advanced when put together. How much general electronics/microcontroller/programming experience do you have, and have you invested in any of the PICAXE development boards available from Rev-Ed/TechSupplies?
 
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moxhamj

New Member
35 metres of shielded microphone cable may not even need RS232. I've run 150 metres of unshielded cable at 0v/5V at 1200 baud with no problems. The only catch with directly connecting picaxes some distance apart is what happens if you send 5V down the cable and the other picaxe is unpowered. That could be solved with a series resistor (eg 1k) at each picaxe input pin. So just two resistors.

Another thing that would help is to use N polarity on serout/serin. N polarity 'rests' at 0V (T polarity 'rests' at 5V).

Get the serial comms working on the bench with two picaxes next to each other (should take less than half an hour with a breadboard) and then add the cable in. Flash a led when a particular character comes in.

The harder part will be the LCD and the keyboard, though there are examples you can follow in the manuals.
 
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lanternfish

Senior Member
What an elegant idea. A theatre I provide technical services to could do with something similar. Will keep an eye on this project and contribute where I can. Cheers
 
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manuka

Senior Member
Good idea! One imagines such control box messages as " This is so boring! Hey- the fat lady doesn't sing for 20 mins- fancy popping out for a quick pint? " PICAXE 18A/X readable PS/2 style keyboards are thick on the ground, & many draw only a few mA. See a 2003 era 18A/X serial keyboard => http://www.picaxe.orconhosting.net.nz/keyb18xa.gif and http://www.picaxe.orconhosting.net.nz/keyb18xa.bas

Shame that I should mention a non PICAXE approach, but with screens & keyboards needed each end it may even be worth looking at direct PC-PC wired serial linking with a just couple of old laptops? This'd no doubt allow such valuable extras as message time stamps too- handy when explaining to the director why you were a tad late back from the local for the final curtain.
 
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MartinM57

Moderator
Dr_Acula said:
35 metres of shielded microphone cable may not even need RS232. I've run 150 metres of unshielded cable at 0v/5V at 1200 baud with no problems.
Click to expand...
Oops - my mistake - I meant generic serial comms (that you can do with 0V/5V) rather than specific RS232 voltage levels. Well I'd start with that anyway, and if I found interference problems then I would look at MAX232-like chips to use full signalling voltages.
 
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lanternfish

Senior Member
manuka said:
Shame that I should mention a non PICAXE approach, but with screens & keyboards needed each end it may even be worth looking at direct PC-PC wired serial linking with a just couple of old laptops? ...
Click to expand...
That concept has its merits. A problem I can see is the time it takes for a reboot at the worst possible moment. With tblunt's idea a reboot would be quick and have minimal impact, especially if a "no response - please resend" error routine was incorporated in the 'transmitting' console.

manuka said:
... This'd no doubt allow such valuable extras as message time stamps too- handy when explaining to the director why you were a tad late back from the local for the final curtain.
Click to expand...
LOL. Was slow on a lighting cue once because sound trogg and myself were looking out a window at some rather lovely young ladies walking past on the street below. Needless to say, didn't repeat that mistake!:eek:

Well, off to the manual to read up on PS/2 keyboard interfacing. After I have written up post on BDU compression and get my GPS2SMS project up and running again.

Cheers
 
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tblunt

New Member
Thanks everyone.
@MartinM57 I'd say im intermediate in electronics. Microcontrolers little and programing intermediate.

The cable length is anywhere from 30-150m. I work in many different venues for short periods and sometimes the mic room is a long way away.
I have just got the software and will now read the manual in detail.
I will spend some time researching this some more and educating myself and the report back on this little project.
As far as I can remember we have always had power available at both ends so having an unpowered box isnt really an issue it was just a thought i had.

The laptops was our initial thoughts however abandoned because of a few things mainly reboot time and space available. We need it to be low profile and the small LCD are perfect but anything bigger than a 7"screen is not useable.

Thanks again

TB
 
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manuka

Senior Member
Fair enough about the boot times, but keep in mind today's XP/Vista bulk has conditioned us all considering lengthy start up delays as normal. Even 10-20 years back, older & slower PCs booted under W98 & DOS in a comparative flash! Many solid state organisers (I still keenly recall my nifty 1984 era Tandy Model 100) were instant on.

Command prompt options exist (Net Send ?), & even quite some decades back in the steam computer era (pre Windows, BT, WiFi & Internet),all sorts of null modem linking batch utilities, "DOSChat" software & commands abounded. Was it Laplink? Interlnk/Intersvr , PCAnyWhere ? I'm showing my age... Stan.

EXTRA:One assumes your control booths are sound proof? Do you use headset & mikes for voice links anyway?
 
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vttom

Senior Member
Another thread on this forum is discussing old PDAs that have real serial ports and terminal emulator software. You could direct-connect a pair of these with a null-modem cable and be good to go.
 
hippy

hippy

Ex-Staff (retired)
Psion 3's and Psion's 5 with a clam-shell design and full keyboard may be ideal for this, either direct connected or as keyboard / display to a PICAXE system. I expect there are other PDA's with suitable keyboards.

The downside of using a PDA is that it's relying on old technology which may be hard to find or get replacements for. One could spend longer getting those to work than building a PICAXE-only system.

Point-of-Sale '7-segment LCD's / VFD's on a stick' would be good for high visibility. I don't know if anyone has any knowledge of how you'd interface to them ... ?
 
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Haku

Senior Member
From my vague memories of being in school plays (many, many, many years ago ;) ) it's always dark behind the scenes, so would a backlit keyboard along with a backlit screen be the way to go?
Something like this if you could find a wired PS2 version - http://gadget-reviews.org/2008/12/brando-wireless-tiny-keyboard/
I always find using my friends laptop a right pain the backside because of the black keyboard in a low light room, so used to using my white Eee where I can actually see the keys in low light.
 
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lanternfish

Senior Member
manuka said:
... EXTRA:One assumes your control booths are sound proof? Do you use headset & mikes for voice links anyway?
Click to expand...
In his original post tblunt said the audience was close to him. The little theatre I supply (volunteer) tech services to has the same issues so com sets are not ideal.

The PDA idea put up by vttom and hippy has serious merit given the cheapness of 2nd hand PDAs.

Back to the original idea. Is it worth starting out with something simple like the SM's console having some buttons that call the half, quarter, standby, go. Other buttons to signal cue number, alert audio, lighting and misc error. Of course the latter assumes operator/tech is savy enough to diagnose the error quickly.

The operator console would have acknowledge, please repeat, "what the ... ", "back in 10 minutes" buttons to respond to messages.

A bit abstract but very simple to implement.

cheers
 
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joely87

Member
I have been doing a little bit of work with serial two wire and LCDS, I have not expiremented with the length of wire you require so i will leave that up to the others.

I will suggest a SERLCD sparkfun backpack will make your life easier if you only have little programing experience. As you are in australia i get all my sparkfun gear from Little Bird Electronics
http://www.littlebirdelectronics.com/products/serial-enabled-16x2-lcd-white-on-black-5v.

They did not have a good rep a while ago but they are amazing now. They have a chat feature you can used for simple question. Also you do not have to get this particular screen. you can also just buy the backpack and solder it to any HD44780 LCD. Have a look on the sparkfun site aswell, if there is any thing you want that Little Bird dont have on their website just ask them and they will get it.

are you going to use computers/laptops as the keyboard imput OR an old standalone keyboard?
 
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