I see it as 1.4 seconds on, 1.8 seconds off. Is that what you want?

Yes,i was getting about 1.5 seconds on and 2.0 seconds off.

If you want it to light while it is in the light then flip the LDR and variable resistor over again.

Forgot to change that back,thanks....

Btw,general purpose diode like 1N4148 should be fine to use...right?

 

Bill changed the output transistor to an emitter-follower so it no longer inverts.

Yeah,i didn't notice that...thanks for mention it.

The duty-cycle is so high that a 9V alkaline battery will last for about 26 hours with the LEDs slowly dimming the entire time if the output transistor is fixed. The LEDs will look bright for only about 7 hours.

Would it be any difference if i get 9v from 6 units of AA....will the battery last a bit longer.

I blink my very bright LEDs for only 30ms and the battery lasts for months. But I use Schmitt-trigger Cmos logic ICs, not Cmos 555 ICs.

My project is to flash kinda like x-ray radiation safety warning light....so i'm not sure if yours fit to what i want. Maybe if you can help me with the design if it can save the battery a lot time longer.

 

Would it be any difference if i get 9v from 6 units of AA....will the battery last a bit longer.

Six AA cells weigh about 5 times as much as a little 9V battery (that uses six tiny AAAA cells) so they will last about 5 times longer.

My project is to flash kinda like x-ray radiation safety warning light....so i'm not sure if yours fit to what i want. Maybe if you can help me with the design if it can save the battery a lot time longer.

Yours turns the LEDs on then off then on then off .....
Mine blinks the LEDs briefly so the battery lasts a lot longer. Blink at a faster rate if you want.

 

When I designed my long life flashers I designed for 30ms of on time (that is 0.03 seconds). I believe AudioGuru did something similar. If you want long life, make that duty cycle small. Timing for 30ms on/1 second off works out to 3% duty cycle.

I thought you were after a light source before (still do).

 

You guys are right....it would be better if i shorten the on period so it would saved the battery a lot time longer. As for it i also might change power supply to 12 v with 8 units of AA but still use 4 units led to light,so the current will be less used.

Another problem is to make Schmitt Trigger with less hysteresis. I didn't get about to put a pot of pin 5 of the 555 connected to the LDR.
How does it operate?
Does the circuit look like this?

 

You should use a much lower duty-cycle (reduce the value of the 1M resistor until its current is too high when the LEDs are supposed to be off) to save battery current.
The lower value of the 1M resistor wasting current is the problem with using a 555 IC in this application. If a Schmitt-trigger logic gate is used instead of this 555 IC then there is no current when the LEDs are turned off.

You should add a 2.2k resistor in series with the base of the transistor to limits its current to 2.5mA.

 

You guys are right....it would be better if i shorten the on period so it would saved the battery a lot time longer. As for it i also might change power supply to 12 v with 8 units of AA but still use 4 units led to light,so the current will be less used.

Another problem is to make Schmitt Trigger with less hysteresis. I didn't get about to put a pot of pin 5 of the 555 connected to the LDR.
How does it operate?
Does the circuit look like this?

Nope. Look at the internal structure of a 555. One of the nice things about 555s is the simplified schematic is pretty accurate.

Put a simple variable resistor on pin 5 to ground. It has some draw backs, but it also works. When the resistance gets under 1KΩ the voltages on those points will also be pretty low.

 

You should use a much lower duty-cycle (reduce the value of the 1M resistor until its current is too high when the LEDs are supposed to be off) to save battery current.

I like to reduce it as low as possible,but it would be a meaningless (as a flash warning light) if it hardly to notice at all. If it could flash brightly continuously around a day or two,that should be perfect.

 

When an LED has an "on" time less than 30ms then it begins to look dimmed. If its "on" time is 30ms and it blinks at twice per second then it will be a very visible warning light that uses low current so the battery will last a long time.

If the electronics uses low current, the LED "on" time is 30ms and it blinks at twice per second at 25mA then the average current from the battery is only 1.5mA per string of series LEDs so the battery will last a long time.

 

When I designed my long life flashers I designed for 30ms of on time (that is 0.03 seconds).

Bill,i just noticed that you design your flasher without diode but still manage to have a small duty cycle(3%). A bit confuse from the cookbook that the basic multivibrator can adjust from 50.1-99% duty cycle.

 

Point to the circuit you are talking about.

If it is this one...

CMOS 555 Long Duration LED Flyback Flasher

Then you missed Q1, which is a simple transistor inverter.

97% duty cycle inverted is a 3% duty cycle.

Using the Vcc power supply rail instead of ground is pretty much the same thing.

 

Now ,i get it...between the duty cycle and frequency.with the whole reason to put and inverter to switch the cycle. Now,i have reduce the cycle around 10% which i think would be ok for my project and try use back the transistor as the switch for ldr. Seems to be ok,but there is one problem which the led supposed to off when dark is present.What happen is it stays on the whole time...i would guess it might relate to the inverter but still didn't get it. Here i attached my schematic.

 

You removed the connection off Pin 7 to between R1 and R2. This is not an optional connection, refer back to the links I gave on post #53. Pin 7 discharges the capacitor, a critical function for this kind of oscillator.

 

Sorry,my mistake....the connection is actually there.I accidentally remove it from the schematic without notice. Is still like that where the leds kept on illuminate the whole time when dark,but it work fine when there is light where the leds is flashing like i want to.

 

When an LED has an "on" time less than 30ms then it begins to look dimmed. If its "on" time is 30ms and it blinks at twice per second then it will be a very visible warning light that uses low current so the battery will last a long time.

If the electronics uses low current, the LED "on" time is 30ms and it blinks at twice per second at 25mA then the average current from the battery is only 1.5mA per string of series LEDs so the battery will last a long time.

I'd take your advise,its better to get minimal flash but enough to give warning sign.

 

Is still like that where the leds kept on illuminate the whole time when dark,but it work fine when there is light where the leds is flashing like i want to.

I explained in my post #60: "Bill changed the output transistor to an emitter-follower so it no longer inverts. Then the circuit lights the LEDs continuously when the second Cmos 555 is reset (you want them to be off)".

You should wire the 555 and LED driver transistor like the second 555 in post #65.

 

You should wire the 555 and LED driver transistor like the second 555 in post #65.

If i change it,will it effect the duty cycle?

 

If i change it,will it effect the duty cycle?

Of course the inverting transistor will invert the duty-cycle. Then you must add the diode as shown in post #65.

 

Hi guys,its been a while....been busy doing something else but at last i manage to get back to my project. I have been testing on duty cycle for my circuit and it seem getting a much much lower cycle is not bad at all .And finally it work like i want it to do....thanks to you guys that been helping me a lot. I really appreciated it.

Now,i trying to add up some led to 8 units(red,2.5v fv,25mA) and using 12 v supply voltage.

There is one more thing i would like to ask.What consideration should i take on the value of the bypass capacitor. Does it matter if i use a lower one like 100 uF for the circuit?

here i attached my circuit.

 

The base-emitter diode of the transistor is shorting the output of the Cmos 555. Use a 1k resistor in series with the base.

Your LEDs are not 2.5V. They might be anywhere from 2.2V to 2.8V. If they are 2.2V then the 82 ohm resistor will create a current of 39mA and burn out the LEDs. If they are 2.8V then they will be dim with only 9.7mA.

So buy thousands of LEDs and measure them all and select 2.5V LEDs or use strings of three LEDs with a series 200 ohm current-limiting resistor. Then if they are 2.2V then the current is 27mA and if they are 2.8V then the current is 18mA.