I love LED chasers. A bunch of LEDs neatly turning on and off on a precise timing - lights running one way, then the other way… It's relaxing, soothing, and hypnotic.
There are so many LED chaser/scanner/sequencer circuits out there, some are made with discreet transistors, some based on logic ICs, and more and more others are using microcontrollers.
There is one thing in common with all of the LED chaser circuits you find on the net - none of them can operate with just one alkaline battery!
Most of us know that LEDs need at least 2.2V or so to light. Blue and white LEDs require even higher, typically 3.2V. So obviously you can't use just one AA battery to operate an LED chaser. But we all know that there is Joule Thief that boosts voltage high enough to light any LEDs. Why not use that to operate an LED chaser?
Missing Link
Joule Thief is a nickname for this simple voltage boost circuit, predominantly used to light LEDs with one battery cell. However Joule Thief can be used to power more than just LEDs. I decided to power a microcontroller circuit with Joule Thief. (Although I ended up still lighting LEDs.)
There are so many LED chaser/scanner/sequencer circuits out there, some are made with discreet transistors, some based on logic ICs, and more and more others are using microcontrollers.
There is one thing in common with all of the LED chaser circuits you find on the net - none of them can operate with just one alkaline battery!
Most of us know that LEDs need at least 2.2V or so to light. Blue and white LEDs require even higher, typically 3.2V. So obviously you can't use just one AA battery to operate an LED chaser. But we all know that there is Joule Thief that boosts voltage high enough to light any LEDs. Why not use that to operate an LED chaser?
Missing Link
Joule Thief is a nickname for this simple voltage boost circuit, predominantly used to light LEDs with one battery cell. However Joule Thief can be used to power more than just LEDs. I decided to power a microcontroller circuit with Joule Thief. (Although I ended up still lighting LEDs.)
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Wave JT is not only powered by a single AA battery, but it's feature rich. Here are the highlights of the Wave JT.
- Compact & streamlined design.
- Uses only one AA battery (or any 1.5V battery you can hook up to).
- Works well with rechargeables (NiMH or NiCd) too.
- Eight LEDs, each with its own 256 level brightness control.
- Energy efficient - works even with a run-down battery, down to 0.6V (0.8V to startup).
- Versatile PIC microcontroller based LED chaser/scanner/sequencer.
- Many light animation patterns to choose from.
- Speed control via multiple taps of a button (double/triple taps to speed up/down).
- Start up "Quick-select" mode to choose from top 8 of over 16 patterns.
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But my biggest question is, if you are starting and stopping the current through the inductor with the uC pwd, what waveform are you using? PWM, clear timer on compare?
The microcontroller simply turn the PWR pin on and off to keep the voltage within target. No PWM. I'm using the A/D converter to read the supply voltage of the microcontroller, and turning the PWR pin accordingly.
Aki
With this project, the Zener diode only comes in to play when the switch SW1 is closed. Microcontroller turns of the base current to Q2 when the voltage is high enough, but lower than 5.1V. This effectively regulates the output voltage of the Joule Thief without letting the Zener to conduct. (Explained in the above chapter.)
This method not only saves a few parts, but is also more energy efficient - since there's no current wasted by Joule Thief when there's enough voltage.
Thank you for posting your circuit though. Other people looking to use Joule Thief as a standalone DC power supply will benefit from your circuit.
Aki
For inductor I recommend to stay within 47 to 100 uH, but higher values would work ok. Capacitor C2 also can be larger, but larger ones are also physically larger - not good for this project...
Aki
Referred you to a Question and voted ;-)
What question?
A
You can purchase the kits and PCBs at theLEDart.com.
http://www.theledart.com/blog/wave-jt-kit