1011001011100010101 etc.....

 So, it's been a few weeks since the last update, and overall, while there has been progress, it's also been a case of two steps forward one step back regarding the Arclight(nee Arcturus) signal transmission.

 

From previous, you'll know the plan was a 50ms pulse @ 1800hz followed by 5 bytes of serial data. 

This was done by outputting a PWM signal at 1800hz(50% duty) via the CCP module in PWM mode, then after 50Ms switching to the output from the Eusart module to transmit the serial data.

 

On the picaxe, this worked. It could be transmitted and received.

 

When switched to a Pic, it didnt. A lot of time was spent working on this and working on WHY it wasn't working - on the principle that "It works on X, so why not on Y"

It turns out that a lot of people where having similar problems with Eusart modules when they are transmitted over IR. Wierd but hey-ho. Mind you, those modules were only ever intended to trsansmit data over wires.

 

But wait... it works on the Picaxe Chips....

Yep. it did. And I think I've figured out why.

 

Now, the Picaxe chips are based on PIC chips (You can revert them back to pic chips if desired, but can't then reset them back to picaxe). I was using the Pic 08M2 for the sensor and the 14M2 for the transmitter. The relevant pic chips underpinning each are: 08M2 = Pic12F1840 POicaxe 14M2 = Pic16f1825

On these two Pics, the output pins for the Eusart modules, as well as being able to be fed into the DSM module to create a modulated signal are on a set output pin, which can't be changed.

The PICAXE chips have two serial output and two serial input commands. SERIN/HSERIN and SEROUT/HSEROUT to input/output respectivley. I was using the SERIN/SEROUT commands, which looking through the details of each commands, and the fact that Serin/Serout use different pins than the fixed pins on the Pic leads me to beleive that these, while using part of the hardware Eusart module, also have a fair amount of Firmware wrapped around them, and as such, don't quite work the same way.

 

And that's the difference. 

I suspect if I canged the Picaxe output to the HSERIN/HSEROUT command that the transmission would likely fail as it does on the Pic chips.

 

Bit of a bugger really.

 

So... how to get around it?

 

More research followed, around the various IR transmission protocols that are out there in the world, and the majority all work on a similar priciple. That of a variant of Pulse witdth modulation. In this, a signal is sent with varying duration pulses, and the length of each pulse dictates wether the pulse represents a binary '1' or binary '0'. These pulses can be sent at a set frequency or not depending on how you set it up.

The drawback is you have to manage the pulse width yourself - "Bit-Bang" the data in common parlance, which needs a chunk of calculations* for both transmit and receive setup.

But the priciple is straightforward, and I can also transmit the data at the 'classic' 1800hz so that legacy equipment (WoW gear, and the kit made for the Bab 5 game) will see the signal as a single hit, and Arclight sensors will see their signal as a single hit. Will it work with other systems that have grown from the old WoW standards? Don't know. If they look for the 1800hz 'hit' signal by counting pulses then probably, but I beleive the data part will be ignored. If they check the frequency by checking the pulse width, then it'll likely not work. Still, don't know as I haven't got any of the kit to try it with, and, if I'm honest, I'm only including the 1800hz frequency in to support the Picaxe based PPG's that were made for Babylon 5.

 

Still, overall despite effectivley taking a year off developing anything, it's coming along nicely.

PIC'ing the chips :)

Well, PIC migration has started in earnest now…

 

Following a few setbacks…..

Bit of a pain when the programmer you have is no longer supported.

More of a pain when the new programmer doesn’t have one of the useful features of the old one – I’ve moved to Pickit3 programmer from Pickit2. The only drawback I’m finding is that the Pickit3 programmer does not seem to have the capability to act as a serial communication interface – by which I mean with the Pickit2 (and picaxe cables) you could use them to communicate with a terminal program on the PC so you could see the results of serial output, or simulate a serial input – which was rather useful.. actually.. fairly critical in being able to get the serial communication part of the Arcturus signal working. It’s also useful in seeing what is being sent to the audio modules to ensure the correct commands are being sent.

I can’t do that with the Pickit3.

Bugger.

I CAN get a usb-serial interface doohickey that will let me do that and that should be arriving tomorrow all being well. Even though it’ll mean an extra thing cluttering the workbench – But that’s a definite 1^st world problem 😊

Once that arrive I’ll be able to figure out what I’m doing wrong with the serial signal at the moment and get it sorted. Then after that all I need to do is internally modulate the signal and the hardware side of the migration is sorted – It’s just a case of writing the code to slot it all into.

YAY 😊

 

HOWEVER…. Yeah.. There is always a however ain’t there 😊

 

What I CAN’T do (at least for the emitter circuits) is a pin for pin replacement of Picaxe for Pic.

Why? Well, it seems that for some of the functions of the processor, rather than using the hardware modules on the underlying Pic, the Picaxe uses software equivalents.

For example: Interrupts

Interrupts are useful little things that enable you to tell the processor that something has happened and to well.. interrupt what it’s doing and deal with it. This is useful for things like detecting button presses or incoming signals (Y’know… nothing much.. just something that makes up most of what I want 😊 ).

Now, the Picaxe 14M2 chip I use has external interrupts (for button presses) available on pins 5,6 & 7. The underlying Pic chip (16F1825) has external interrupts on PortA – that is, pins 2,3,4,11,12 & 13 – While this is handy as I need more interrupts, it’s a pita – not a HUGE pita as it’s a  minor change going forwards. The biggest problem is the sensors – Luckily the interrupts on the pic used in the sensors are fine – the possible issue with those is the signal input/reading may need to change pin. Handily though if that’s the case, the sensors boards are modular so it’s not too much to change them out (at the cost of some Veroboard, couple resistors, IC chip socket and some soldering).

It’s a similar case with the serial comms, the Picaxe has it on a number of the pins, but the Pic there are a choice of 2 pins – and one of those is the one that will output the modulated signal so that narrows it down even more. The Picaxe has a dedicated command to output/input via the same pin as the Pic.

 

Still. Things are coming along steadily, and given that the Picaxe chips were initially intended as a teaching/learning tool, they have certainly done that, as if I’d have gone straight into the Pic development, I wouldn’t have known where to even begin so in that respect they have been perfect.

 

But it’s time to move on.

Mind you, it also helps that the Pic chips are slightly less than half the price of the Picaxe based on them 😊