open source modular pda (Picaxe Inside)

i've been looking at pda's lately and looking that most of them realistically they don't seem to feature what i want not even the high end ones

so in my own little world (my garage) i've thought of a "modular pda" concept,

the idea consists of 1 chip eg a picaxe on an 8bit parallel bus + module select lines

there would then be a few modules on the bus each with their own chip which would control the hardware it is connected to, eg a screen module ,an sd card module, ps/2 keyboard module,

then i'm thinking of a simple to learn scripting language where access to all of the modules is easy and simple addressing system

any ideas


Senior Member
I don't think the Picaxe will provide the kind of response times that you get even with older PDA's (less than 100MHz processors) and certainly won't match the 400MHz CPUs currently available.

If you want to adapt an existing PDA to do things your way. you can get NSBasic for Windows/CE and Palm OS PDAs. I've done some work with the Palm version and find it very easy to use (aside from the quirks of any PDA OS).

I'll second Papa's thopughts. At 2000 instrdcutions per second (at 4mHz) response time will be very slow

You can pick up Palm PDA's pretty cheap ($25) on eBay. There is a lot of computing and display power built in. The Picaxe chips make a great front end to interface to the real world.

One note, the Handspring Visor PDA has a TTL level serial interface and can be directly conected to a Picaxe.

Search the forum for more info.

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Technical Support
Staff member
I suppose it comes down to what features you want, in what format, and at what price but I'd have to be pushed hard to promote a PICAXE PDA over a commercial design.

Given that we're seeing the emergence of £99/$199 PC's I wouldn't expect to better that with a PICAXE. The disadvantage as technology improves is lack of access to previous core technologies; serial in particular. WiFi and Bluetooth are great but costly to connect to PICAXE / Real World (TM) hardware, a USB to Serial interface can be 10%-20% extra on price.

Too old and the PDA's have serial but often aren't easily programmable, too modern and it's all new fangled wireless, but there should be something in between which gives serial and is very programmable. Something with serial and wireless is useful. There should be plenty of good, cheap, second hand options on eBay and elsewhere.


Senior Member
Agreed- 4MHz ( & interpreted at that) will never compete with a raw 400MHz! All the slickly integrated features would be impossible to neatly replicate too. Further more-with the rise of ever smarter cell phones-PDAs at any speed are increasingly viewed as quaint,& you'll probably be given a swag of dusty ones just by putting your hand up. I've recently been handed a <3 yo. $$$ Palm Tungsten T5 (with particularly good BlueTooth features) that a cat had apparently piddled on -the owner couldn't be bothered cleaning things up! 5 minutes with a soapy cloth & it was as good as new.
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for speed the main big boss chip i was thinking somthing along the lines of one of the newer pic32's when they comeout, or even somthing like the pic18f8722 at 40mhz there are also other processors out there that run quicker as well

the picaxe's would be more suited to the modules

the lack of access with most of the interpreters to things like some of the ports is what gets puts me off them

the wonder of a modular pda is that if you don't need a bluetooth module then it simple could be unplugged

if you need say a serial connection then it's a case of hook it up write scripted application and away you go,

another idea that hit me is instead of having a scripted language
this would be possible with the pic18f8722 just copy over whatever program that is required to be executed over to some sram and have it executed from there that way applications for it could be wirtten and executed by the raw pic rather than an interpreted script

it would have to be compiled for the pic specifically but it would speed things up and give access to everything


Senior Member
As others have pointed out, the idea of trying to compete head-on with an iPhone or similar is silly, but I do think there is some demand for a handheld "device" that is easy to interface to electrically (for hobbyists), yet still provides a screen and keypad for i/o (like the picaxe, not all things require tons of real-time number crunching). There is a commercial attempt at that you might think is neat: - In fact, this is probably exactly what you're thinking of.

If you insist on going the Picaxe-route, yours truly and a fellow named XNederlandX have already made our own attempts at it:

Picaxe-based "Laptop":
-My laptop was just an 18X, 24LC512, serial display and a keyboard, and it even had a simple peripheral bus (along with a programming language/compiler/interpreter and text editor)

Picaxe-based "Organizer":
Well, I thin there is some mileage in a simpler device that can be easily programmed. But sadly it'll take more than an 18X. And if it's anything like DPG's trans-oceanic canoe then we'll be waiting a long time :)
trying to compete with other pda's isn't really the idea in fact would be nuts ,

i was probably being a little liberal when i said "pda"

what i've got in mind is more of a general use by hobbyists/techi nerds thing, somthing you could say have your shopping list on tied in with a barcode scanner and be able to look at price changes while you shop (after the program is written for that prupose)
i'd like to see a barcode scanner on somthing low cost like a palm zire...
you could then take the same device and say plug in a serial port and use it for a serial terminal for your picaxe project,

the transatlantic canoe is quickly turning into a high altitude balloon since i got given a full cylinder of helium a few months ago


Senior Member
the transatlantic canoe is quickly turning into a high altitude balloon since i got given a full cylinder of helium a few months ago
You could always combine both ideas? I'll keep my eyes peeled,both marine & aerial,over here in NZ!