28 pin project board problem

Gramps

Senior Member
Greetings from Ft. Myers Florida,
We're lighting 8 LEDs on pins B.7 through B.0.
Using input pin C.1 as a momentary contact switch.
Pin B.0 will not light, Can a pin be burned out?
Here's the code:
Thanks, Gramps
Code:
main:
    let dirsA = 16
    let dirsB = 0
    let dirsC = 0

Cell_7_3:
    high B.7
    if pinC.0=1 then
    goto Cell_7_5
    end if
    goto Cell_7_3
Cell_7_5:
pause 1000
    low B.7
Cell_7_7:
    high B.6
    if pinC.0=1 then
    goto Cell_7_9
    end if
    goto Cell_7_7
Cell_7_9:
pause 1000
    low B.6
Cell_7_11:
    high B.5
    if pinC.0=1 then
    goto Cell_7_13
    end if
    goto Cell_7_11
Cell_7_13:
pause 1000
    low B.5
Cell_7_16:
    high B.4
    if pinC.0=1 then
    goto Cell_7_18
    end if
    goto Cell_7_16
Cell_7_18:
pause 1000
    low B.4
Cell_7_20:
    high B.3
    if pinC.0=1 then
    goto Cell_7_22
    end if
    goto Cell_7_20
Cell_7_22:
pause 1000
    low B.3
Cell_7_24:
    high B.2
    if pinC.0=1 then
    goto Cell_7_26
    end if
    goto Cell_7_24
Cell_7_26:
pause 1000
    low B.2
Cell_10_4:
    high B.1
    if pinC.0=1 then
    goto Cell_10_6
    end if
    goto Cell_10_4
Cell_10_6:
pause 1000
    low B.1
Cell_10_8:
    high B.0
    if pinC.0=1 then
    goto Cell_10_10
    end if
    goto Cell_10_8
Cell_10_10:
pause 1000
    low B.0
    goto Cell_7_3:
 
Last edited by a moderator:

westaust55

Moderator
Hello Gramps,
A quick look through your code on an iPhone (away from home and no access to the PE to simulate) found no reason it should not work.

So onto your question:
YES it is possible to burn out an IO pin if the current draw is too high.
The limit is 20 mA per pin and typically around 100 mA max for the entire chip.

A few questions:
What voltage is your circuit operating at?
What value of resistor do you have in series with each LED.?
Does the LED operate ? - remove the PICAXE and use a jumper from supply to the B.0 pin on the socket to power from the socket through the resistor to the LED.
 

westaust55

Moderator
Further questions:
Are you using the PICAXE AXE020 project board?

If so, then are controlling the LEDs through the ULN2803 driver chip?
If not then a link to what you are using will help.

If so these are rated at 800 mA per channel and a somewhat less if all channels are in use/on at once.

Are you sure that the LED for Pin B.0 is corrected the right way/polarity?
 

Gramps

Senior Member
"PICAXE AXE020 project board?"
Yes.
"controlling the LEDs through the ULN2803 driver chip? "
Yes.
If we swap the LEDs around pin B.0 still doesn't work. Polarity is right, LEDs check good on another pin..
Don't recall ever using B.0 on this board.
I suppose the ULN2803A chip could have failed on that pin, too.
Operating voltage 5 volts regulated power supply.
Resisters are 300 ohms each diode.
 

premelec

Senior Member
Try loading a program that just turns the problem pin on and off a second or two at a time and check the voltages [with multimeter] on PICAXE driver chip to localize the problem.
 

Gramps

Senior Member
We popped out the 28X2 And installed the 28X1 chip that came with the board.
Behold it's working!!
Edit, So that pretty much proves the pin is smoked, correct?
 
Last edited:
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