The Shield... Why?

[cactusface]

Hi All,
I like the idea of the shield and was quick to cobble it together, and make it do something. Firstly just use an EEprom and flash the on board LED, wait! no you can't do that!! Who put the LED on the 12c bus, could it not just go on a plain old I/O pin like A4,B6,7 etc..

And why those ST voltage regs, that don't have the standard pinouts, while those from TI, Nat semi, etc DO, and you could then choose to fit any you care too, LDO or otherwise.
I may have missed something, often can't see the wood for the trees..

Moan over. Thanks for a great forum.
Regards
Mel.

 

[hippy]

The on-board Shield Base LED is on the signal line used for best compatibility with other shield system designs. Atmel processor based shields have hardware I2C placed on the analogue A.x pins but that is not compatible with PICmicro hardware. Unfortunately that means there can be a conflict and compromise required if using hardware I2C and wanting to control the LED. That's one of the reasons there is a header-link which can be removed to disconnect and disable the LED.

The on-board Eeprom is something that is considered to be a useful feature for PICAXE users who want to use it, but that again involves a compromise on use of the LED. On balance the compromise is usually a cost worth paying. The LED can be fairly easily wired to another signal line or a LED on a plug-in shield can be added.

If one wants I2C and LED control, is prepared to have I2C Eeprom on a Shield rather than the Shield Base, using analogue pins or others, it would be possible to code bit-banged software I2C and have that operate in parallel with LED control on the default signal line.

As to the regulators, I don't have an official answer to hand, but would imagine it was a question of capability, cost and performance and perhaps other factors.

 

[Technical]

And why those ST voltage regs, that don't have the standard pinouts, while those from TI, Nat semi, etc DO, and you could then choose to fit any you care too, LDO or otherwise.

It depends on your viewpoint here, different regulators have different pinouts for a reason, in that there is no such thing as a 'standard pinout' within industry.

We specifically did not want people to use 7805 type, as they would not work well in this circuit. One advantage of this different pinout is it actually physically stops people using these popular, but very dated and inefficient, old regulators.

However the vast majority of customers buy a kit anyway, so the type is not that important to most customers, as they get them provided in the kit!

The LDO regulators used are low-cost, very common and readily available from our shop and places like Farnell/RS/Digikey etc.

www.techsupplies.co.uk/REG006
www.techsupplies.co.uk/REG007

 

[cactusface]

The Shield..

Hi All,
Well I suppose I should have known it was a matter of compatibility!! Not having taken much notice of the original Atmel designed Shields.... As Hippy says it's no trouble to wire the LED on to another pin on the shield proto-board, as this is where all the extra bits go anyway!!

Voltage regs well I've just used a TI UCC283-5 LDO reg on a board powered by 4xAA HiMh batts and get a consistent 5.2v from less than 6v, so I see the point of using them, but not the point of forcing people to use them. If the unit is to be mains powered it does'ent really matter, do's it?

PS: Technical just tied the links you supplied, did'ent think the LDO regs were that cheap, perhaps I saw them somewhere else (at about £1.25) , so I will be ordering a few next time round. It rather blows a hole in my comments above...
Regards
Mel.