556 timer power supply

[unseen wombat]

So I've discovered that you can't power a 556 timer with a joule thief. The pulsed DC current causes the timer to reset every time it pulses. (I think that's the reason anyway). I'd like to run my lucid dreaming mask circuit with the smallest battery possible, which also actually has a decent capacity. The 12V A23 works, but the battery life of 60 mAh is abysmal. (My circuit draws about 7mA when it's not flashing, and 17 when it is). I'd much rather put an N size in there, but it only outputs 1.5 volts, and it needs to power two 555 timers, and two red LED's. Is there anything I can use to do this? With as few components as humanly possible. Could I somehow (simply) modify the joule thief to supply a constant DC supply instead of pulsed DC? Or would that be defeating its purpose?

Thanks everyone.

 

[ericgibbs]

So I've discovered that you can't power a 556 timer with a joule thief. The pulsed DC current causes the timer to reset every time it pulses. (I think that's the reason anyway). I'd like to run my lucid dreaming mask circuit with the smallest battery possible, which also actually has a decent capacity. The 12V A23 works, but the battery life of 60 mAh is abysmal. (My circuit draws about 7mA when it's not flashing, and 17 when it is). I'd much rather put an N size in there, but it only outputs 1.5 volts, and it needs to power two 555 timers, and two red LED's. Is there anything I can use to do this? With as few components as humanly possible. Could I somehow (simply) modify the joule thief to supply a constant DC supply instead of pulsed DC? Or would that be defeating its purpose?

Thanks everyone.

hi,
You could try adding a 1N4001 on the collector of the transistor, as a half wave rectifier charging a small cap.
See what dc voltage you get.

 

[k7elp60]

Another possibilty is use CMOS versions of the 555 timer, and go to coin size lithium battery that is 3V. Most Red LED's only need about 2V to turn them on.

 

[unseen wombat]

So put the diode in series with the one leg of the toroid going into the collector?

Would a 1N4148 work? I have a bunch of those on hand.

 

[unseen wombat]

Another possibilty is use CMOS versions of the 555 timer, and go to coin size lithium battery that is 3V. Most Red LED's only need about 2V to turn them on.

Unfortunately, I have to turn on 2 of them. And will the 3V battery power the timers? I thought they needed 4.5 volts minimum. Maybe CMOS timers are different though.

 

[pc88]

If you want to make a low-power device, I'd use a microcontroller:

The Lucid Dream Machine - Instructables - DIY, How To, tech, life - Let It Glow! Entry

cre.ations.net - Creation: Face-mounted Lucid Dreaming Mask

 

[ericgibbs]

So put the diode in series with the one leg of the toroid going into the collector?

Would a 1N4148 work? I have a bunch of those on hand.

hi,
Not in series.

Keep the transistor and transformer wiring the same, connect the anode of the diode to the collector
of the transistor, connect the cathode of the diode to say a 100nF cap.

Connect the other end of the cap to 0v.

Measure the dc votage on the cap with a meter, lets know what it is,?

 

[unseen wombat]

Eric. Thanks for the suggestion. I only have one 1N4148 with me, and I do have a 0.1uF cap, so I tried those. I don't have my multimeter with me, so I couldn't measure the voltage, but it didn't work to run the 555 timer. It only stayed in "on" mode, like before. Is there a difference between the 4148 and the 4001 though? And since the joule thief supplies all positive DC voltage (though it is pulsed DC), won't a rectifier just output the same pulsed DC? I thought rectifiers were only for clipping off the negative portion of an AC sine wave. Am I wrong?

PC88, I'm not a smart man, but I know what a 555 timer is.</forrest> LOL. Microcontrollers and programming are beyond me. Also, won't that increase the cost of my device dramatically? Timers and resistors and caps are cheap. A programming board is expensive, right? I never looked into it, so I don't know.

 

[crutschow]

And since the joule thief supplies all positive DC voltage (though it is pulsed DC), won't a rectifier just output the same pulsed DC? I thought rectifiers were only for clipping off the negative portion of an AC sine wave. Am I wrong?

A rectifier (diode) allows current to flow in only one direction. Thus the rectifier allows the positive pulses to pass which are filtered by the capacitor to smooth the pulses and give a dc voltage, but it keeps the voltage on the cap from being drained by the transistor when it is in the "on" part of its cycle.

 

[audioguru]

Look in Google for Solar Garden Light Circuit. Many garden lights use a fading red, green and blue LED that has a driver chip in it. It operates from 3.6VDC and the solar garden light has a circuit to stepup the 1.2V AA size rechargeable battery cell. The circuit is a little more complicated than a Joule Thief.

If your LED needs 3.6V at 20mA then a 1.5V battery cell must provide nearly 60mA which is too high for a small button battery cell. A 3V coin cell might provide 30mA for a few minutes.

An ordinary 555 has a minimum operating voltage of 4.5V and has an operating current of 3mA to 6mA.

A Cmos 555 has a minimum operating voltage of only 1.5V but its output current is low when its supply voltage is less than 5V. Its operating current is almost zero.

Adding a 1N4148 diode and a capacitor makes a peak detector. Then there will be DC across the capacitor. A 1N4001 diode is too slow.

 

[Krumlink]

@Audioguru: Do you have any links to a good circuit as described? I google but did not find any great ones.

 

[Krumlink]

Never mind found a good one, just remove the battery if needed:

**broken link removed**

 

[audioguru]

Hi Krumlink,
You found a Joule Thief circuit with another transistor to turn it off when there is enough light for the solar cell to charge the battery.

 

[Krumlink]

I did, tricky!

 

[Boncuk]

How about low current LEDs?

They consume just 2mA. Using a CMOS timer circuit chances are good for a long battery life.

 

[audioguru]

How about low current LEDs?

They consume just 2mA. Using a CMOS timer circuit chances are good for a long battery life.

I have never seen an LED that is bright with a current of only 2mA, except the cheap narrow focussed ones that can't be seen if they are not beamed at you.

 

[unseen wombat]

Thanks guys. So, is this what you're saying I should do? I should wire my 555 in parallel with the capacitor on the joule thief? I made a sketch of how I understand it. Is it right?

I looked into the microcontroller they used for the lucid dreaming circuit that PC88 posted. It's very nice, and simple, with hardly any components. I also saw some DIY PIC prorgramming boards and some for sale for < $30. Maybe it's not beyond my ability, especially if I just have to download the code from the Instructables site. I'll definitely research this more. Thanks.

 

[ericgibbs]

hi,
Ive redrawn the diode.

I have no idea what voltage to expect across the capacitor.

Just connect the LED's with a small resistor in series across the 100nF.
Leave the 555 out of circuit for the test.

Measure the voltage on the cap.

If the voltage can drive the LED's, try a 1uF in place of the 100nF

 

[unseen wombat]

I just checked it, and the voltage across the 100 nF cap is 3.3 volts. When I connect the LED's in parallel with the cap, it's not powerful enough to drive more than one of them. The single LED lights up nicely though. But when two are connected, they flash brightly for a second, then dim down to almost nothing so I can only see that they're on at all in the dark. When I connect the 555 timer, I get one flash, then nothing at all, not even a dim light, as far as I can see. I checked the voltage on the 555's capacitor, and it's oscillating between 2.1 and 2.2 volts. (I think for some reason, it's not discharging like it should).

Is there any other thing I can try?

 

[HarveyH42]

I've had no problem running several of my flashing LED boards off a Joule Thief, with a 1N914 and 1 uf cap. Theses use low voltage AVR microcontrollers, even an RGB fader with separate LEDs.