2013-12-08 Blue Blinky Used As A Remote Control Finder

I got a frigid greetings by email from Kirk, where it’s a bone-chilling -20 deg. F in Winnepeg, CA.   He’s building a similar device to find a misplaced object.  I have a few other Ideas I’d like to go over.

The Blue Blinky uses a Joule Thief circuit, which works with any color LED because it can overcome the 3 or more volts that white or blue LEDs require.  However if you can use some color other than blue or white, there are other circuits that might work well.

The Blue Blinky consists of two parts: a Joule Thief and a flasher which turns the JT on very briefly.  This flasher is capable of flashing a LED by itself if the supply voltage is greater than the LED’s forward voltage.  So if the supply voltage is two 1.5V cells in series or a single 3V coin cell, the flasher circuit alone should run most colors other than blue and white.  Some green LEDs require up to 3V, so they may have to be tested beforehand.

The TE Flasher

Now, the above flasher uses a supply voltage of 3V, and works okay with most lower voltage LEDs.  But say I want to use a lower voltage LED with 1.5V cell.  How do I increase the voltage up to 2 or more volts to light the LED?  The Joule Thief is an easy way to do this.  But there is another way, without a coil or transformer.  This is by charging a capacitor across the 1.5V cell,  then connecting it in series with the 1.5V cell to give 3V.  This is what I did with the TE flasher.  The schematic shows the 100 uF capacitor.  When the BC327 turns on, it puts this capacitor in series with the 1.5V, so up to 3V is across the LED.

I have also built a few of the Blinky Boost flasher that uses two capacitors, so it can put out over 4V to the LED.  This is even more complex than a Joule Thief, but it seems to use less power and the battery seems to last longer.  However every Joule Thief can be modified to use less current, but no one has explored this method in depth, so Blue Blinky type flashers that use a JT having low current are not often found.  One point has to be remembered: a Joule Thief has a typical efficiency of 50%, which means you get less light for a given supply current, or you need more supply current to get the same amount of light.

A couple things about the Blue Blinky

I used two 680k resistors because they were easier to find than a single 1.3 Meg resistor.  Also I figured that I might like to put a 1 meg resistor in one place on the circuit board, and a 470k trimpot in the other location.  That way, I could adjust the flash rate somewhat.

Also, the 68k resistor determines the flash length.  The smaller its value, the shorter the flash duration. A longer flash uses more current.  The .01 uF capacitor could be any value down to .001 uF and it shouldn’t make much difference.

Capt. Hook’s Ticking Sound

Another thing I’d like to go over is the use of sound to locate the remote control.  If I connect a receiver out of a telephone handset between the  LED and negative, it gives a clicking noise.  The high voltage that could be generated by the inductance of the receiver’s coil can be damped by putting a resistor across the receiver.  This also lets me control the volume, so that the remote doesn’t become an annoyance when it’s near.  The receiver could be too big, so another possible ‘speaker’ that could be connected in series with the LED is an ear bud.  They are small, but they are typically low impedance, around 16 to 32 ohms.  I haven’t tried this yet, so it’s something I’ll have to experiment with later.

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