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LED 'smoothing' question

F

frenchy

Jan 1, 1970
0
If a regular incandescant bulb (like a #44) is replaced with an LED,
and the original bulb was made to sometimes have a slow on-to-off
effect (by flashing it very fast for different amounts of time for
each pulse), is there a simple way to give the same smooth look to the
led, like with a capacitor or something like that? The bulb strobes
smoothly since the filament does not cool off between the pulses, but
the led is either totally on or off thus it has a flickering
appearance when this strobing is being used. (When on solid, the led
looks normal of course.) This application is a pinball machine, 6v
ac, using one of the new LEDs specially made to be directly
substituted for the #44. Thanks!
 
D

D from BC

Jan 1, 1970
0
If a regular incandescant bulb (like a #44) is replaced with an LED,
and the original bulb was made to sometimes have a slow on-to-off
effect (by flashing it very fast for different amounts of time for
each pulse), is there a simple way to give the same smooth look to the
led, like with a capacitor or something like that? The bulb strobes
smoothly since the filament does not cool off between the pulses, but
the led is either totally on or off thus it has a flickering
appearance when this strobing is being used. (When on solid, the led
looks normal of course.) This application is a pinball machine, 6v
ac, using one of the new LEDs specially made to be directly
substituted for the #44. Thanks!

Well...it's not basic but I used a PIC microcontroller to solve that
problem.
D from BC
 
F

frenchy

Jan 1, 1970
0
Well...it's not basic but I used a PIC microcontroller to solve that
problem.
D from BC>>

To add - this would need to be something connected directly to the
bulb, or between the bulb and the voltage going to it, I can't modify
the circuitry that's sending the power to the bulbs.
 
J

Joerg

Jan 1, 1970
0
D said:
Well...it's not basic but I used a PIC microcontroller to solve that
problem.


I did the same thing with the MSP430, resulting in an aircraft beacon
type light that blinks "softly". It can also be done with a cap but
since the LED is basically a current driven device with a (somewhat)
fixed voltage across it the cap would have to be larger than with a bulb
of same current level. However, one has to carefully check whether the
electronics can drive such a concoction. Opamps can oscillate, other
stuff could fry when it sees a huge capacitive load.
 
J

Joerg

Jan 1, 1970
0
frenchy said:
To add - this would need to be something connected directly to the
bulb, or between the bulb and the voltage going to it, I can't modify
the circuitry that's sending the power to the bulbs.
Do you know what kind of circuitry that is? Reason I ask is that it
might not like a capacitive load.
 
R

Rich Grise

Jan 1, 1970
0
Do you know what kind of circuitry that is? Reason I ask is that it might
not like a capacitive load.

The electronic pinballs & such that I used to fix used SCRs and half-wave
rectified AC. To turn the light on, you'd bias the SCR's gate, to turn it
off, you'd ground the gate.

So I don't think an LED circuit would hurt it - what I'd try is replace
the dropping resistor with two of half the value, in series, with a cap
from the junction to power return.

Have Fun!
Rich
 
R

Rich Grise

Jan 1, 1970
0
I did the same thing with the MSP430, resulting in an aircraft beacon type
light that blinks "softly". It can also be done with a cap but since the
LED is basically a current driven device with a (somewhat) fixed voltage
across it the cap would have to be larger than with a bulb of same current
level. However, one has to carefully check whether the electronics can
drive such a concoction. Opamps can oscillate, other stuff could fry when
it sees a huge capacitive load.

Nothing to do with the OQ, but I wouldn't "softly" blink an aircraft
beacon - I'd use strobes, because they're so much better at catching
your eye in your peripheral vision.

Cheers!
Rich
 
J

Joerg

Jan 1, 1970
0
Rich said:
The electronic pinballs & such that I used to fix used SCRs and half-wave
rectified AC. To turn the light on, you'd bias the SCR's gate, to turn it
off, you'd ground the gate.

So I don't think an LED circuit would hurt it - what I'd try is replace
the dropping resistor with two of half the value, in series, with a cap
from the junction to power return.

AFAIU he wants to smooth the flicker when the drive is PWM'ed. If it's a
SCR as you said maybe they do that by skipping half-waves unless it's a
dimmer circuit. A SCR might not like the current spikes a "smoothing
cap" causes. It probably depends how much margin it has. Worst case
there could be a loud pop and whiff of smoke.
 
J

Joerg

Jan 1, 1970
0
Rich said:
Nothing to do with the OQ, but I wouldn't "softly" blink an aircraft
beacon - I'd use strobes, because they're so much better at catching
your eye in your peripheral vision.

On many aircraft you have both types. Soft blink is also needed for
obstruction lighting where you are often not allowed to strobe. You'll
see that on some of the radio towers, for example.
 
F

frenchy

Jan 1, 1970
0
AFAIU he wants to smooth the flicker when the drive is PWM'ed. If it's a
SCR as you said maybe they do that by skipping half-waves unless it's a
dimmer circuit. A SCR might not like the current spikes a "smoothing
cap" causes. It probably depends how much margin it has. Worst case
there could be a loud pop and whiff of smoke.>>

I definitely don't want to have a risk of damaging the circuitry, this
pinball is not cheap and this isn't really some
big problem, just makes the leds stand out when they are being pulsed
so they are noticeable as being leds.
I wouldn't mind trying it on one of my older pinballs but none of them
do this pulsing, only my very new (and expensive) ones do.
You are correct they are just powered by a transistor either on or
off. They are slowly
strobed by turning on and off and changing the length of each pulse.
I wouldn't have any
idea of what cap or resistor values to use for this app.
 
J

Joerg

Jan 1, 1970
0
frenchy said:
I definitely don't want to have a risk of damaging the circuitry, this
pinball is not cheap and this isn't really some
big problem, just makes the leds stand out when they are being pulsed
so they are noticeable as being leds.
I wouldn't mind trying it on one of my older pinballs but none of them
do this pulsing, only my very new (and expensive) ones do.
You are correct they are just powered by a transistor either on or
off. They are slowly
strobed by turning on and off and changing the length of each pulse.
I wouldn't have any
idea of what cap or resistor values to use for this app.

You'd have to experiment. Some data would help, like voltage and wattage
of the lamp that was in there before, and the peak current of the new
LED. The resistor in front of the LED works to protect the circuitry but
only if the lamp voltage had been much higher than the LED voltage.

The cap would have to be experimented with. Make it as large as it takes
to remove the flicker. But have others look at it, too, because one
person might see flicker that others don't.

If the lamp voltage had been so high that the resistor has to drop
several volts life gets easier: Then you can use two resistors in series
and tap off for the cap in the middle. -> Smaller cap.
 
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