Aurora Mini 18

My obsession of this year is full-color LED. I have made Aurora 9x18 as a result. As much as I love the scale of Aurora 9x18, I also wanted to have something smaller, perhaps something that can go on a costume.

Here's Aurora mini 18. It has 18 full-color/RGB LEDs on a smallest possible circle. With a single PIC microcontroller, changing 18 RGB LEDs smoothly is reaching the technical limit. With the new PIC with wider supply voltage, the circuit is simplified compared to Aurora 9 bar, and use of two AA or AAA batteries (3V operation) or one Lithium battery is now possible.

Step 1: Concept & Circuit

Like Aurora 9 bar, Aurora mini 18 borrows its circuit from Aurora 9x18. Operating principle is exactly the same. Just extended the hardware and software to control more LEDs.

One of the new 24F line of PIC microcontrollers is PIC24FV16KA302. Unlike the similar PIC24F series controllers which are 3.3V limited, this controller can operate fully up to 5V. This eliminated the need for the 3.3V voltage regulator, and simplified the LED driving circuits. The resulted circuit with fewer parts count made this Aurora to be very compact.

Step 2: PCB & Parts

Aurora mini 18 uses surface-mount technology (SMT). If you've never built anything with SMT, this might be a good opportunity to try out. You will most likely realize that there's nothing to fear about SMT. (If you are not familiar with soldering, you might get your feet wet with something simpler than this though.)

The high-quality, custom made PCBs as well as the full kits are available at a reasonable price. Please view the details at "For Sale" section of the forums.


Parts

Here is the list of parts. All except LEDs are available at Digi-Key (digikey.com).

• 1x 10k Ohm (0603)
• 3x 220 Ohm (0603)
• 3x 2.2k Ohm (0603)
• 18x 150 Ohm (0603)
• 2x 0.1uF (0603)
• 2x 10uF (1206)
• 3x Q1x: MMBT2907A
• 1x PIC24FV16KA302 (SS)
• 18x Tricolor LED (common-cathode) (SparkFun COM-09264 should be identical) http://www.sparkfun.com/products/9264
• 1x Tactile Switch
• 1x 3 - 5V power supply: regulated AC adaptor, 4 NiMH, 2 AA/AAA batteries & case, single cell Lithium battery, or USB cable
• 1x 2 pin Molex header (right-angle recommended) (optional)
• 1x 2 pin Molex connector with corresponding terminals (optional)

There are many places to purchase LEDs. I source LEDs directly from China via AliExpress. Takes a few weeks for delivery, but the prices are great. (If you are purchasing a lot of LEDs.)

You can substitute transistors if you have something compatible.

Step 3: Tools & Supply

• Tweezers
• Soldering iron
• Solder (flux core. go for the highest quality solder you can afford.)
• Soldering flux (Use high quality flux. Low quality flux causes problems! ChipQuick brand recommended.)
• Wire cutter (I recommend this one.)
• http://www.amazon.com/Xuron-170-II-Micro-Shear-Flush-Cutter/dp/B000IBSFAI
• Microchip PIC programmer (supports PIC24FV16KA302 and capable of In-circuit programming through a standard 6-pin ICSP connector, such as PICKit 3, ICD 2, ICD 3.) (PICKit 2 does not support PIC24FV16KA302.)
• Computer running Windows or Mac OS
• Magnifier visor or other visual aid device (optional, but highly recommended)

Step 4: Notes on SMT

If you are already familiar with SMT, you can skip this step.

There's no need to use reflow method (solder paste & bake) to build Aurora mini 18. Since there are only a few components to solder, it's quicker to just hand solder everything.

It's very helpful to use high quality flux when you solder SMT components. I'd say it's the key to successful hand soldering of SMD. Apply a small amount of flux to the PCB pads before placing the device, then solder. If you haven't done this before, you'll feel like your solder skill has suddenly improved :)

Step 5: Assembly

Please download and print the "Parts Placement Chart". Use this to identify/guide where all the parts go.

I recommend following the order listed. Also be mindful of electrostatic charge. Use anti-static desk mat if you have one. Or place aluminum foil under the PCB like I do.

Washing the Board
Solder everything _but_ the switch. Then wash the PCB with water. I've had many problems of LED flickering a while after the assembly due to the slight short circuit caused by flux residue. Even with high quality flux, solder joints can accumulate dust, and with moisture in the air creates electrical conduct. The problems went away after I started washing my PCBs.

Wash PCB in warm water and detergent. Use old toothbrush to scrub the solder joints, making sure all of the flux is off. Rinse very well with warm water, and dry completely using a hair dryer. (Very important)

If you solder the switch by mistake, please don't wash the board. Switches can not be wet. Instead, use cotton swabs and alcohol or flux cleaner to clean the flux residue.

After the PCB is cleaned and dry, solder the switch, and assembly is finished!

Step 6: Choose Power Supply Connection

The power supply voltage needs to be between 3 to 5V DC. If you are using a wall wart, make sure it's regulated. (Most of 5V wall warts are regulated type, but if you are unsure, measure the output voltage. Unregulated wall warts output much higher than 5V without a load.)

The supply can be as low as 3V (with a decreased LED brightness of course), so you can use variety of batteries; two Alkaline batteries, one Lithium cell, three or four NiMH batteries, etc.

Square pad on the PCB is negative, and round pad is positive. Be very careful not to apply voltage in reverse polarity! It will most likely destroy the unit - can't tell - I never tested.

Another cool thing is to use USB power. Aurora mini 18 draws less than 150 mA, so most (if not all) USB ports should work.

Step 7: Electronic Check & Program the PIC

Check carefully for bad solder joints and parts placements errors. Before moving on further, take out your multi-tester and check the Ohm reading of the power connector and ICP connector pads. Make sure there are no shorts.


Then fire up your PC, launch Microchip IDE. If you don't have it, please download it from Microchip website. Scroll down to the bottom of the page to find the downloads. (http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en019469)

Here are the steps for the IDE ver.8.xx:

1. Select programmer - click on "Programmer -> Select Programmer" choose your programmer here. (Note: PICKit 2 doen't support PIC24FV family)
2. Select device - click on "Configure -> Select Device" and choose PIC24FV16KA302 under "Device" menu.
3. Import HEX file - click on "File -> Import", and open the HEX file downloaded.
4. Click on "Programmer -> Settings", and click on "Power" tab. Then turn on "Power target circuit from PICKit 3", and set the voltage to 5V. (Note: this setting may not be available with some programmers. If that's the case, connect power source to the Aurora.)
5. Click on "Programmer -> Reconnect". Click "OK" if you get the "Voltage Caution". You should see some messages in the "Output" window. Check connections, etc. if you get errors. 
6. Programm the PIC - Make sure to insert the header pins into the ICSP holes of the Aurora and hold it securely. Click on "Programmer -> Program" to start the programming. It should only take 20 seconds or so, and you will see "Programming/Verify complete" message in the "Output" window.

That's it!

I used PICkit 3, but other programmers such as ICD2, ICD3 should work. (PICKit 2 doesn't work with PIC24FV16KA302)

Just use those 5 holes/pads on the PCB as though they are the female connector. Give a bit of tension sideways to make sure the electrical connection is stable.

*** Firmware update is available - download at http://www.theledart.com/blog/archives/1012 ***

Step 8: Enjoy!

I hope you enjoy the beautiful and hypnotic color patterns as much as I do. I have a few well tweaked patterns in current firmware to chose from. A push of the switch changes the pattern. Hold down the switch for two seconds turns the lights off.