LED on/off Time Issue They Keep Dying

Thread Starter

Walkerandy48

Joined Oct 7, 2018
16
Hi

I have recently used a Pic16F883 to run an LED network 12 by 4 hence 48 blue LEDs.
A 100ohm resistor was used to limit current. fwd volt drop of LED 1.2v, 0402, 5v supply. K8048 vellerman programmer using ICSP.
E.g. A4 is used as the positive supply to 4 LEDs, C0,C1,C4,C5 used as negatives all with 100ohm Res.
Program turns on A4 and then C0,1,4,5 respectively in a loop, A4 remains on, however I have tried clrfPORTA after first loop and back on again to no avail.
I sped up the flash rate from 1/s until the LED appeared to be on, I am not sure what the flash rate is but it's not that fast
All worked well until suddenly C5 used as the open drain or negative side of the LED started staying sort of half on,by this I mean all LEDs in the network that used C5 as their negative stayed on half lit until their turn came up and then illuminated correctly.
My next attempt to reprogram IC is not recognised, presumed blown.
My best guess is that one or more LEDs failing have shorted and blown the IC.
The LEDs were purchased quite cheaply from U.K. Company via China.
Anyone has any ideas would be appreciated.
 

crutschow

Joined Mar 14, 2008
25,631
Are you trying to power all the LEDs directly from the Pic?
If so, that will overload the Pic.

Post your shemtic as it's not clear what you are trying to do.
 

dl324

Joined Mar 30, 2015
11,822
Anyone has any ideas would be appreciated.
Start by posting a schematic instead of trying to describe your circuit with words.
The LEDs were purchased quite cheaply from U.K. Company via China.
You should assume that any semiconductors you purchase from China are probably rejects or counterfeit. Save yourself some aggravation and buy from reputable sources (Mouser, Newark, Jameco, Digikey, etc). Don't buy from eBay, Amazon, AliExpress, etc.
 

KeithWalker

Joined Jul 10, 2017
1,288
Start by posting a schematic instead of trying to describe your circuit with words.
You should assume that any semiconductors you purchase from China are probably rejects or counterfeit. Save yourself some aggravation and buy from reputable sources (Mouser, Newark, Jameco, Digikey, etc). Don't buy from eBay, Amazon, AliExpress, etc.
I buy all my electronic parts from Aliexpress. I have only ever received one item which did not work, a 2.8" OLED display. My money was immediately refunded. I re-ordered the part and received a good one.
 

oz93666

Joined Sep 7, 2010
737
..You should assume that any semiconductors you purchase from China are probably rejects or counterfeit. .
Nearly all semiconductors are made in China ... the few which are made in the west , are made on the same machinery the Chinese use in their factories ... usually western companies buy from china , triple the price and sell to people who believe west is best ...

I buy vast amounts of leds , always from eBay at the cheapest price ... Usually the problem with leds is heat dissipation ... drive below max current for a long life.
 

nsaspook

Joined Aug 27, 2009
7,722
Nearly all semiconductors are made in China ... the few which are made in the west , are made on the same machinery the Chinese use in their factories ... usually western companies buy from china , triple the price and sell to people who believe west is best ...
This is just not true. It manufactures less than 20% of the semiconductors it uses domestically. Their semiconductor import costs are about $200 billion annually.
China does buy a lot of junk from final test operations in Asia or have older process technologies that are below quality standards.
 

oz93666

Joined Sep 7, 2010
737
I was of course referring to leds , not computer chips or semiconductors in general....



the "Americas" accounts for 10% of production , and that figure must include those made in Sth America too ....

There's also the myth that there's massive amounts of "junk" substandard led's ... there maybe a few % from the production line that fall into this category, but if an led manufacturing line was turning out more than this , the problem would be fixed ....

My experience is the led chips are fine , but when buying complete lamps or light fittings ,Chines manufacturers quoted power cannot be trusted , a lamp sold as 18W will often consume only 6W of electricity
 
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Thread Starter

Walkerandy48

Joined Oct 7, 2018
16
I am flashing them in turn so only one LED is on at any time.
I am maxing the IC outputs a little @25mA.
A lot of the LEDs have blown and had to be replaced.

Thanks
 

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dl324

Joined Mar 30, 2015
11,822
I am flashing them in turn so only one LED is on at any time.
I am maxing the IC outputs a little @25mA.
A lot of the LEDs have blown and had to be replaced.
With a 5V supply, the maximum LED current would be I = V/R = (5V-1.2V)/100 = 38mA.

It's questionable whether the PIC can sink that amount of current. But without timing information, max PIC sinkcurrent, and LED specs, we can't venture a guess as to why the LEDs are burning out.
 

ElectricSpidey

Joined Dec 2, 2017
1,316
First I find blue LED’s having a forward voltage drop of 1.2 a little odd.

Second the OP stated that there were 48 LEDs, so from the description of the lighting sequence there have to be 12 lighting at a time?

So I’m just too confused to help.
 

Thread Starter

Walkerandy48

Joined Oct 7, 2018
16
Ok thanks all.
I have purchased some LEDs from RS and will try these.
I will also try increasing the current limiting resistors.
Lastly I will check all of the parameters of my components.
 
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