28x and voltage regulator getting hot..

M

mark.duyvesteyn

Member
My basic download circuit for a 28x isn't working, and both the voltage reg and pic is getting hot. I borrowed the picaxe of a friend so not to sure about its history. If it has been perviously damaged will it continue getting hot and drawing large current?? the only parts that are connected is the download circuit and two outputs to a transistor (through a 10K res) the reset pin is held high. No resonator is fitted as is is optional i think..

any words of wisdom?
 
W

westaust55

Moderator
28x and voltage regulator getting hot

Can you upload a sketch of your circuit, or better still a photo showing the wiring to the voltage regulator and PICAXE chip.

Have you measured the voltage output from the voltage regulator?
Is it 5Vdc?

Is the PICAXE supply connected the right way around?

Try with say a 25 Ohm resistor as the only load on the voltage regulator.
Is it getting as warm with 200mA current flow?
 
C

chipset

Senior Member
if its getting hot you are either overloading the cicuit by excess current draw however if you only have the basic download circuit set up its shorted. Im going to guess that something is either hooked up incorrectly. What makes me go that route is that the power supply is getting hot. You need to work backwards to find out what is causing the short. Either way you have something hooked up wrong an dmay have already damage the components. Time to get a logic tester, test light or meter and start diagnosing the problem. I think you wired something up wrong.
 
M

mark.duyvesteyn

Member
heres a shot from above and below

DSC00639.JPG
DSC00640.JPG

Any ideas, sorry bout the non color coded wires..

the reset pin is broken in the picture, but was connected. circles indicate joints. Everything down stream works fine (a 5v input on the transistors trip the relays)
 
Last edited:
D

Dippy

Moderator
Sorry I can't spend time checking the photos.

Have you done ANY continuity checks with a multimeter to check for short-circuits?

Did you insert PICAXE in the right way round?

Any stray hairy bits of solder? (Check with magnifier).

Doesn't that regulator need any capacitors? Have you 'scoped it?

Did you check the power at the i.c. pins before inserting PICAXE?
Or did you just shove it and switch it on and pray?

Have you got a proper Rev-Ed board to test the PICAXE?

Oh dear. Your friend will blame you for breaking his PICAXE and will demand a replacement :(
 
S

SilentScreamer

Senior Member
I'm betting you have a short somewhere, either that or are your transistors connected incorrectly? Try removing components as a process of elimination.

I'm assuming the connected tracks on the bottom right hand corner of the 2nd photo are intentional.
 
E

eclectic

Moderator
It's probably not relevant now,
if the Picaxe is baked, but
from post #1

"..for a 28x . .... No resonator is fitted as is is optional i think.."

If it's a 28X, then it requires a resonator.

e
 
hippy

hippy

Ex-Staff (retired)
This has all the hallmarks of a short somewhere, probably on tracks to PICAXE pins as it's getting hot. Remove the PICAXE and check every socket pin to every other with a continuity tester.

Then check there's no continuity across any holes which should have cut the veroboard tracks.

Also check for unexpected continuity across adjacent tracks. I tend to run a craft knife between tracks to clear any potential shorts.

Make sure the PICAXE is in the right way round. It's traditional to show a board so that the notches / pin1 of chips are to the top, your board appears to be rotated to that.
 
H

hax

New Member
I don't see any capacitors anywhere!!

You need a 100uf before the regulator, a 10uf after the regulator and a 0.1uf at the picaxe power pins.


You probably have the whole circuit PWMing at the moment and broadcasting over the radio waves!
 
H

hax

New Member
Also, are you using an unregulated plug pack? You should use a regulated 9V plug pack with this circuit to decrease the heating seen in the regulator.
 
M

mark.duyvesteyn

Member
i was powering it directly of a fused 12v SLA battery

that should provide a pretty clean source shouldn't it?

Ive checked again for continuity between pins and tracks, still nothing so i might put it down to a dead picaxe.

Will grab another one tomorrow and see how things go. thanks for your help.

mark
 
D

Dippy

Moderator
Do you have a PICAXE proto board of any type to test the PICAXE in?

It really is a 'must have' for testing and for newby 'My First Download'.
It removes several 'variables' to eliminate faults.
I risk suffering the Wrath of Stan, but I'd always recommend that before My First Breadboard - unless you can have over-the-shoulder advice from someone like Stan.
 
hippy

hippy

Ex-Staff (retired)
mark.duyvesteyn said:
i might put it down to a dead picaxe.

Will grab another one tomorrow and see how things go.
Click to expand...
Assuming your PICAXE is now dead and you have nothing to lose by 'killing it further'. With the PICAXE fitted check the regulator gets hot. Without the PICAXE not fitted, does the regulator still get hot ? If so it's probably a fault on the board.

If you plug a new PICAXE into a board with a fault then you may destroy that as well. So ideally you want to find what the fault is first.

There's more on the board than was originally suggested so perhaps the circuit design is flawed or there is a construction error. If those are relays, one mistake can be installing the back-EMF diode in reverse; when the transistor/FET driver is enabled it then presents a near short across power rails, though that should not overheat the PICAXE.
 
W

Wrenow

Senior Member
Dippy said:
Do you have a PICAXE proto board of any type to test the PICAXE in?

It really is a 'must have' for testing and for newby 'My First Download'.
It removes several 'variables' to eliminate faults.
I risk suffering the Wrath of Stan, but I'd always recommend that before My First Breadboard - unless you can have over-the-shoulder advice from someone like Stan.
Click to expand...
Following this advice, and also not cobbling my own serial download cable, would have saved me literally hours of frustration on my first attempt to get it all working.......

But... I did learn something (icluding to buy the ... download cable and some official Picaxe project boards).:D

Cheers,

Wreno
 
H

hax

New Member
If you use an SLA battery you still need capacitors around the regulator and the chip.

The 12V is going into the regulator and is being "chopped up" to make 5V. So while a SLA is better than a transformer, you still need to filter after the regulator.

You also need to filter at the chip because the picaxe itself creates noise on the power line and it can be affected by the noise it produces.
 
B

BeanieBots

Moderator
Agree with Haxby.
Some regulators are oscillators without any capacitance.
A regulator alone is NOT a power supply any more than a transistor alone is an amplifier.
 
L

lanternfish

Senior Member
Haxby said:
The 12V is going into the regulator and is being "chopped up" to make 5V. So while a SLA is better than a transformer, you still need to filter after the regulator.
Click to expand...
Just a couple of corrections to the above discussion -

A 7805 is not a switch mode power supply (SMPS), so it doesn't "chop up" the 12V. It regulates it down to 5V. The 7805 contains a current source, voltage reference and error amplifier to maintain the output at 5V for an input of approx. 7V to approx. 30V.

One problem with running a 5V regulator above 15(ish) volts is the internal heat generated. A rule of thumb I was given was that the input voltage should be no more than 2 times the output voltage (when operating close to 75% max. current) to keep this loss to a minimum.

My understanding of the 7805 regulator capacitors are:

Input Capacitor - To smooth ripple on the input voltage, especially if from a half-wave rectifier. Even a full-wave rectifier will have a small ripple voltage.

Output Capacitor - To improve stability and transient response. Sudden switching of high(ish) current loads can cause the output to dip slightly if not kept up by this capacitor

Have built/noticed on some 7805 circuits for microprocessors, 100n caps from input and output to ground to provided added 'noise' filtering on the supply lines.

Hope this helps the discussion and understanding of linear voltage regulators.

Cheers
 
M

MartinM57

Moderator
^^^^
Nice post :)

One trick I have seen, but not used myself, is to put two 78xx regulators in series if there is a reasonably high current draw and a large Vin-Vout difference e.g. a 7812 then a 7805, to reduce heat build up in a single regulator
 
A

Andrew Cowan

Senior Member
Power dissipation = voltage drop times current.

12V to 5V at 1A = 7W.

T0220 package = 15 degrees/W

7 x 15 = 105 degree rise in temperature. I think a heatsink is needed at high currents.

Maximum load of PICAXE: 25mA.

12V to 5V at 25mA = 0.175W = 2.6 degree temperature rise. No heatsink needed.

A
 
Last edited:
B

BeanieBots

Moderator
We might be straying a little here.
A simple regulator with nothing more than a PICAXE as load should not be getting luke warm let alone hot even with 20v on the input to the regulator.
Absolutley no need for any pre-regulation or load dumping/sharing.
 
M

mark.duyvesteyn

Member
I took the pic out of the circuit and put it in a friends breadboard which was already set up and it worked!

I took it out of the breadboard and put it back in mine and it didn't work.

Checked my circuit, everything looked fine, so put a new picaxe in and it worked first time.

Its working fine now, but i am at a loss as to why this 1 picaxe didn't like my circuit and did like the on in the bread board.
 
S

SgtB

Member
If you wire a PICAXE up wrong on the power side it dies in about a second. If you feel it get warm it's done. I've also fried logic pins in a fraction of a second. They stay high forever after that. Turn off the power supply when building is the moral of the story. :)
 
hippy

hippy

Ex-Staff (retired)
It seems odd that the PICAXE works in your friend's breadboard but not your own circuit yet a new PICAXE does work in your circuit, but perhaps the two circuits are not exactly the same ?

A PICAXE can run with outputs shorted to 0V and will respond correctly to firmware checks and downloads, even run some programs, but as soon as a program sets those outputs it will likely fail and cause damage to the PICAXE - And things will start getting hot.

Hopefully whatever the problem was has cleared itself in the process of poking about and swapping chips over.
 
A

Andrew Cowan

Senior Member
Last time I plugged in an 18X the wrong way, it got hot and broke EEPROM locations 15-20.

Works perfectly apart from that (although I wouldn't put that chip into a project).

Heat does odd things to chips.

A
 
You must log in or register to reply here.
Top