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8 transistors = 1 tip120?

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Pulsing w/ 60ma

not 120ma
maybe by puting in parallel ??
with 64 leds total I wonder if the viewing angle really matters?
the arrays are on 1/2" wide - 8 seperate boards to fit into a 2" round tube
shall we say high density.
question is will the 7556 drive the 8 darlingtoin transistors and the piezo unit.
another item I need to consider will a 50ms pulse allow the leds to achieve full brightness.
the triggering of the 7556 needs a low signal. If the signal stays low will the circuit continue to keep triggering? or will it cease after one cycle./
 
not 120ma
maybe by puting in parallel ??
the LEDs will survive 50ms blinks at 60mA. Two strings are 120mA total.

with 64 leds total I wonder if the viewing angle really matters?
the arrays are on 1/2" wide - 8 seperate boards to fit into a 2" round tube
shall we say high density.
If the LEDs shine around the circle then they might have a narrow searchlight pattern, not much up and not much down.

question is will the 7556 drive the 8 darlingtoin transistors and the piezo unit.
The piezo might need 5mA and each darlington needs 0.5mA so the total current of 9mA can be driven by the 7556 IC.

another item I need to consider will a 50ms pulse allow the leds to achieve full brightness.
A 50ms pulse duration appears at full brightness.

the triggering of the 7556 needs a low signal. If the signal stays low will the circuit continue to keep triggering? or will it cease after one cycle./
if the trigger pin stays low on a monostabe timer then the output stays high and it never times out. You can capacitor-couple the trigger signal so that it gives a pulse.
 
f the trigger pin stays low on a monostabe timer then the output stays high and it never times out. You can capacitor-couple the trigger signal so that it gives a pulse.

just put a capacitor in series with trigger switch to ground?? or
 
Uncle $crooge,

I learned something new when I looked at the ONsemi data sheet for the 2N2222A. They actually have a graph of the the saturated gain for various collector currents. Although Fig. 4 is "Typical" it is very interesting. I ignore the Fairchild data sheet since it still contains typographical errors from the first edition published forty years ago (VCEsat test condition 10V???).
 
f the trigger pin stays low on a monostabe timer then the output stays high and it never times out. You can capacitor-couple the trigger signal so that it gives a pulse.

just put a capacitor in series with trigger switch to ground?? or
The trigger pin must have a resistor to the positive supply to make it high after the capacitor-coupled pulse ends.
 
add this??

the circuit I am using is the same as the 2 stage time delay circuit I have attached.
the circuit says the time out even if the trigger is held low.
but will it start to retrigger again?? if held low.
In the circuit I am using the 7556 all the (#) refer to the 555 pins.
I added a resistor cap combo but thinking I should drop the cap and just go with 100K or ? resistor??
will get back to you
hover snap has a problem??
 
You really need to state your exact requirements as we are just going around in circles.

How many LEDs do you want to illuminate?
What colour are they?
What is your supply voltage?
What is the flash-rate and what is the ON time and OFF time.

From this we can offer an instant solution.
 
How many LEDs do you want to illuminate?
looking at one flash of 50ms. a total of 64 white LEDs
have 8 led arrays driven by 8 darlington transistors (see previous posts w/ diagrams). Each array=1 darlington has 2 sets of 4 LEDS in series w/ 100 ohm resistor or there abouts for each set of 4 leds. Caculated at 120ma per led array of 8 leds.
supply voltage is 18v for leds and 12v for 7556 timer(output drives the 8 darlingtons and a pizeo buzzer.
leds planing on using
**broken link removed**
the led arrays are mounted as an 8 sided unit inserted into a 2" dia. tube
not sure if the flash will be blindly bright or ??
 
add resistor cap for trigger

inserted a resistor/cap to trigger but maybe just the resistor. The switch is showen as a monintary NO switch but the unit will basically be triggered as a NO switch (not monentary)
need to avoid retriggering when switch is closed for extended time. Just want one flash.
the 7556 is set up as per **broken link removed**
the 2 stage time delay circuit. It says circuit will time out if the trigger is held closed.
the (#) denote the pins on the 555
 

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A 100 ohm current-limiting resistor for the Chinese LEDs does not allow 60mA:
1) If the LEDs are typical at 3.4V each then their total is 13.6V for four in series.
2) The saturation voltage loss of a darlington transistor is typically 0.75V.
3) Then the 100 ohm resistor has a voltage across it of (18V - 13.6V - 0.75V)= 3.65V.
4) Then the current is 3.65V/100 ohms= 36.5ma.

If the LEDs are 3.0V then their current is 52.5mA.
If the LEDs are 3.8V then their current is 20.5mA.
Measure each LED, sort them then calculate the resistor for each string.

Like I said, a 555 will never time-out if its trigger pin is held low. It says so in the datasheet and that is why the input capacitor that I recommended is used in the 555 article you found. The article does not have page numbers so I attached the schematic here. His capacitor is 10 times more than yours but I think yours is better because it responds quicker.
 

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Your circuit already had the trigger pulse parts.
I wish you made the addition of the resistor/cap combo in RED so i could see it.
Get rid of these parts.
 

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The surface-mount Chinese LEDs might be a nightmare to solder.
They have 3 LEDs inside. Are you allowed to connect them in parallel?
Is the max allowed continuous current in each LED 30mA or is the max 10mA for each for a total of 30mA?
 
I don't know

I will contact the company and ask
the pads for connection are different than what one would think.
I can't read the data sheet from the internet site. looked up plcc-6 leds and got the pad demensions.
weather there right??
will contact company.
my circuit already has the rsistors and caps so I guess it will run as pictured.
 
A single Darlington transistor will drive 16 strings of 4 LEDs.
The maximum current for the LEDs should be 30mA, making a total current of about 480mA.
I buy 5mm white LEDs for 3 cents each. These are 20,000mcd and a total viewing angle of 30degrees. The characteristic voltage across each LED ranges from 3.2v to 3.7v. These are readily available from Chinese manufacturers.
You must check the total voltage across each string of 4 to determine the value of the current limiting resistor.
The previous 555 circuit just needs pin 4 taken HIGH.

Colin Mitchell
TALKING ELECTRONICS.com
talking@tpg.com.au
 
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