5 volt regulated Supply

lbenson

Senior Member
Ok. First, I misspoke. I thought I had been running the 14M at 5V, but it was actually 3V3. I switched to 5V, and aside from greater current draw and greater brightness, there was no difference in the ability of the picaxe to light the LEDS repeatedly with no resistors.

since you're in "Destructo Mode" ;), try tying the anode of the LED to V+ and let the PICAXE sink the current
That works too.
14ledtest_0a.jpg

And with all LEDs lit:
14ledtest_all_a.jpg
Here are my measurements of the voltages at 3V3 and 5V with 0V common and with 5V common.
Code:
0V common to cathode
at 3V3
orange 1.97
yellow 2.0
bright green 2.7
purple 3.04
white 2.82
blue 2.77

0 milliamps registered on LCD Volts+Current module for any LED; for all (on for 200ms), 44mA.

at 5V
orange 2.0V 45mA
yellow 2.06
bright green 3.24
purple 3.27
white 3.12
blue 3.05

45 milliamps registered on LCD Volts+Current module for any LED; for all (on for 200ms), 101mA.

V+ to LED anode

at 3V3
orange 3.28 to 1.27V 45mA
yellow 1.20
bright green .35
purple .19
white .35
blue .39

67 milliamps registered on LCD Volts+Current module for any LED; for all (on for 200ms), 77mA.

at 5V (measuring 4.84)
orange 2.81
yellow 2.68
bright green 1.30
purple 1.34
white 1.46
blue 1.48

all (on for 200ms), 190mA.
The code, using pinC.0 to select 0V common for LEDs or 5V.
Code:
' 14LEDtest ' runs leds without resistors
#picaxe 14M

w6=30000
if pinC.0 = 1 then
high b.0,b.1,b.2,b.3,b.4,b.5
do
  for b1 = 0 to 5
'    lookup b1,(5,4,3,2,1,0),b2
    lookup b1,(0,1,2,3,4,5),b2
'    sertxd(#b1)
    low b2
    pause w6
    high b2
    pause 1000
  next b1
  for b1 = 0 to 9
    low b.0,b.1,b.2,b.3,b.4,b.5
    pause 200
    high b.0,b.1,b.2,b.3,b.4,b.5
    pause 500
  next b1
loop
else
do
  for b1 = 0 to 5
'    lookup b1,(5,4,3,2,1,0),b2
    lookup b1,(0,1,2,3,4,5),b2
'    sertxd(#b1)
    high b2
    pause w6
    low b2
    pause 1000
  next b1
  for b1 = 0 to 9
    high b.0,b.1,b.2,b.3,b.4,b.5
    pause 200
    low b.0,b.1,b.2,b.3,b.4,b.5
    pause 500
  next b1
loop
endif
I'm not sure what to make of it all, and I'm not going to quit using resistors. Alleycat's caveat well noted that behavior may well differ between picaxe families (and chip models).

I used these LEDs. The "emerald green" and white ones were quite glaring at 5V.
 
Last edited:

premelec

Senior Member
I guess the bottom line relates to how much power is dissipated inside the IC - from your figures up to .135 watts [.045a & 3 volt drop] - I'm staying with series resistors as well ;-0
 

lbenson

Senior Member
I'm staying with series resistors as well
Right you are. This is in the category of "interesting information", but nothing one should change design practice over.

For what it's worth, it ran for 18 hours with the LEDs commoned low (PICAXE pins going high to turn on), with each of 6 LEDs on B.0 through B.5 with no resistor on a 14M with each LED sequentially on for 30 seconds and then all LEDs on for 200ms and then off for 500ms 10 times.

Then I switched it and it has run the same cycle for 24 hours with the LEDs commoned high (PICAXE pins going low to turn on). No problems detected.
 
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