28x2 Shield Question

[rmtucker]

Finally got my shield soldered up today.
I have changed the 5v regulator for an lm2937et -5.0,And noticed it is getting rather warm when running from 12v.
It will eventually run on a 13.5v supply so the heat worries me.
Anyone got any ideas about a suitable heatsink that would fit in the tight confines of the shield pcb?
I am sure i read somewhere that the 2 regulator tabs have not got to touch each other,maybe the manual?

 

[Buzby]

Are you driving any relays or stuff, or does it just get warm with no loads ?

 

[rmtucker]

No Loads.Just flashing S.13 Led

 

[Buzby]

Er, that doesn't sound right !.

No load = low current = no heat.

Time for some pictures methinks.

 

[rmtucker]

Pictures of what?
What ampage does the shield draw when running at 8mhz?
The manual does mention heatsinking above 12v.

 

[rmtucker]

Oops!,Just checked and the power supply was not regulated,it was putting out 16.5v.
Also checked and the board is drawing 2-3ma when running.
Is it the excess voltage that is causing the heat?

 

[rmtucker]

Can not understand maybe the meter is knackered,i get a higher reading when the s.13 led is off,than when it is on?

 

[Buzby]

Still doesn't seem right.

You've got 11v drop across the regulator, and a 3mA load,

Watts = Volts * Amps = 11 * 0.003 = 0.033W = nearly nothing !.

Your regulator should not be getting warm. ( Unless it can't handle 16v, I've not checked the spec. )

 

[Buzby]

Higher what reading, volts or current ?

Are you sure the supply is DC ?

( We seem to have had a spate of wrong PSUs tonight ! )

 

[rmtucker]

OMG
I have just checked the pinout and they are different for the lm2937 and the ld50v.GULP
How the hell have i done that?????

 

[rmtucker]

Now i am knackered,i can not find a 5v regulator for automotive use with the same pinout,the ld50v is a bit of an oddball pinout?
Wonder if i have knackered anything,strange thing is that it was running and programming ok,Go Figure?

 

[eclectic]

OMG
I have just checked the pinout and they are different for the lm2937 and the ld50v.GULP
How the hell have i done that?????

Welcome to the Cockup club.
Not that anyone here has ever made a mistake.

Bet you'll always read the Datasheet in future.

e

 

[rmtucker]

That beggars belief how it still ran.!!!!
I wonder if i should order a new kit just in case

 

[Buzby]

Welcome to the Cockup club.
Not that anyone here has ever made a mistake.

My latest senior moment was when I was driving B.2 and B.3 in anti-phase to run a piezo louder.
Plugged in two jumper leads which link to the scope on my breadboard.
But they weren't two leads, they were opposite ends of the same jumper.

Now I've got a 28X2 module with two dead pins, and I can't change the chip !.

 

[inglewoodpete]

That beggars belief how it still ran.!!!!
I wonder if i should order a new kit just in case

From my experience, regulators can be fairly tough. I've reversed a 7809 and it got hot but still worked after being connected correctly.

The PICAXE 28X2 contains a voltage regulator of its own and may have survived if it was not loaded.

1. Remove the PICAXE from its socket!
2. Carefully lift (or snip) the offending regulator leads from the board.
3. Solder pieces of single strand wire into the board
4. Bolt the regulator down and criss-cross and solder the wires as they should be connected.
5. Without the PICAXE inserted, apply power and measure the voltages over a 20 minute period. Check the temperature too.
6. If bad, replace the regulator. If good, plug your PICAXE back in and see if it still works OK.

Depending on the voltage actually applied to the PICAXE, parts of it may already be damaged so you don't have much to lose at this point.

 

[Dippy]

Good advice.

But, IPete: "The PICAXE 28X2 contains a voltage regulator..."
- where does that information reside?


I vaguely remember talk of another PICAXE based on the 16F1827 having one.
It was incorrect, though I blame this on Microchip.
In an old data sheet Microchip referred to a capacitor for an LDO.
WRONG.
I queried it with Microchip and they had removed it from latest Data Sheets.
I hadn't seen that.
So, I would hate to see anyone getting wrong info from an error.
Please check latest manufacturer's Data Sheets BEFORE smoking your PICAXE.


Lessons we've learnt:
Just because they look the same NEVER assume....
And ALWAYS read the Data Sheet.
And for some componenets, double-check Tab connection with multimeter.(It only takes a minute of your life).
Always check the circuit schematic/artwork when changing things.


Oh yes, we've all made mistakes!

 

[rmtucker]

Lots of comforting words thank you.
I think i will re-order the shield base (ready Built) and add the lm2937 regulator to the plug in shield that i am making.
Then i can just power the base through the 5v header pin and forget the regulators on the base.
All this just so i can add a Regulator for automotive use?.(i know that is a taboo subject on the forum).
Unless someone can suggest a pin for pin swap for the ld50v regulator.

 

[inglewoodpete]

Rev-Ed's Words

But, IPete: "The PICAXE 28X2 contains a voltage regulator..."
- where does that information reside?

I haven't tried to trawl through Microchip's documentation for these PICAXEs. However, both the M2 and X2 Product Briefs say something along the lines of (this quote taken from the X2 brief):

"They have an internal 3.3V silicon die, but also contains an internal Low Drop Out Regulator, which is automatically enabled when required."​

So I'm trusting the words of Rev Ed. I expect that they have done their research.

Of course, we have no way of knowing what voltage rmtucker's 28X2 was subjected to. That may have been outside the capabilities of any regulator!

Lots of comforting words thank you.
I think i will re-order the shield base (ready Built) and add the lm2937 regulator to the plug in shield that i am making.
Then i can just power the base through the 5v header pin and forget the regulators on the base.
All this just so i can add a Regulator for automotive use?.(i know that is a taboo subject on the forum).
Unless someone can suggest a pin for pin swap for the ld50v regulator.

Good thinking! A good alternative.

Using a PICAXE in an automotive situation is not a problem as long as you stay away from all engine, transmission and safety systems. And you take take full responsibility and accountability for your actions and any consequences of your actions.

 

[rmtucker]

Removed the lm2937 and replaced the ld50v (Well sort of tagged on to the pins that i cut off and it seems to be working fine.)
So off to design a shield and get it cut on my cnc.