32x RGB stick
The RGB stick has 32 individually controlled RGB LED’s. Each color is dimmable with 12-bit resolution. All you have to do is shift in 12 bits for each of the 96 channels, and toggle the latch signal. The four on-board TLC5947′s handle the rest. At 20mA output per channel, the board can draw almost 2A of current and can get pretty bright! Daisy-chain them together with the included headers and control as many as you want.
Note: I originally designed this board to be used as a really good propeller clock, but I haven’t been able to figure out how to spin it and supply power. If someone could give me some pointers I’d really appreciate that
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Please post your questions in the comments section so that everyone can see the answers. Thanks!
|Input voltage:||3.0 – 5.5V
Note: Heat dissipation is directly proportional to input voltage! 4V is recommended, but 5V will still work fine
|Controller:||4x TLC5947, HTSSOP-32|
|Current output:||20mA (±3%) per channel. Customizable from 0-30mA, see below.|
|Maximum serial clock:||15MHz|
|PWM frequency:||~4MHz. Internal oscillator|
|Drop-out voltage:||0.5V (Supply voltage must exceed LED forward voltage drop by this amount)|
|Maximum current:||2A per board. PCB traces support 8A continuous current in daisy chain config|
|Dimensions:||8″ by 0.75″. When chained together via the supplied headers, there is no gap.|
Full brightness in the dark. It’s too bright for my camera to capture properly!
Interfacing this board with an Arduino is extremely simple. Just connect SCLK, IN, and LAT to your Arduino, along with power connections. You can either use software bit-banging to send serial data, or use the SPI hardware peripheral on the ATMega for faster speeds. Here’s an example using software to do the serial transfer: sample code
Shipping costs will be $5 additional for USPS first class mail (estimated two-day delivery). International orders will cost between $10-$15 depending on the country. I’ll include free shipping if you order a bunch of boards.
I will include 4 extra LED’s with each full board/kit in case any burn out or lose proper colors. All headers will be included and soldered (it is slightly difficult to do this with proper vertical alignment)
I’m no longer selling these since it takes a lot of time to assemble and test them, which I don’t have anymore. If you want to buy PCB’s and instructions on how to assemble them yourselves, I’ll be selling them for $5 each.
|$70||Fully assembled with LED’s.|
|$45||Same as $30 below, except with 36x RGB LED’s included.|
|$30||All surface mount components soldered. Provide your own LED’s (cheap off ebay). These boards will be fully tested (making sure all channels have proper current driven).|
|$5||Bare PCB. Bill of materials will be provided with your orders.|
The TLC5947′s are a linear regulator, meaning that the power dissipated by the chip, per LED channel, is proportional to:
Pdriver = (Vcc – Vled) * Iled
This is problematic when having lots of LED’s on. Even with the 2oz copper PCB’s I use, 4 controllers on such a small PCB will heat up quickly. The controllers have an internal temperature shutdown feature, so they cannot be damaged, but for best lifetime of the LED’s, use a low supply voltage. 4V works pretty well without losing any LED drive capability. The board will run fine from a 5V supply though, just don’t touch it with your bare fingers! In the future I may sell inexpensive DC/DC converters that output 4V specifically for use with the RGB stick.
Two RGB sticks daisy chained together, total of 16″.
Multiple RGB sticks can be daisy-chained together side-by-side with no gap, operating as one big shift register. However, the board traces are only rated for 8A max current through it. Higher currents will cause excessive heat dissipation in the board copper itself, but are safe for short periods of time. This is useful if full brightness operation is only used rarely, allowing you to run many boards off one power supply.
If you want to drive a large number of boards from the same serial data stream, simply cut the header pins that connect VCC and ground and connect your power supply to that board. Ensure all power supplies share the same common ground.
I will make available a clock buffer board that goes between two boards (connecting them without a gap). It will buffer both the SCLK and LAT pins with low propagation delay. This is necessary for driving very long chains of RGB sticks. I will include a free one with every cumulative order of four boards, or sold separately inexpensively. More details once they come in.
Custom current value
The TLC5947′s are rated to output between 0 to 30mA maximum. By default, I will send out boards for 20mA. I can customize the current to whatever you like if you’re willing to wait a couple of days. Or do it yourself by modifying the four 0603 resistors R1 according to page 13 of the TLC5947 datasheet (PDF).
Since the human eye is logarithmic, you’ll get more dynamic range out of the LED’s if you run them at lower currents. ie. going from 20mA to 10mA is barely perceptible compared to going from 2mA to 1mA.
The thermal pad is essential for operation at high currents, doubling the TLC5947′s rated maximum power from 2.8W to 5.3W at 25C. In general, soldering the HTSSOP-32 package including its thermal pad (TI’s PowerPad) can be difficult with just a plain soldering iron. However, due to the specific geometry of this board, the thermal pad can easily be soldered with just a plain iron and some alligator clips. Pictures/video coming soon.
- Flux the thermal pad and board. Apply a very small amount of solder onto the thermal pad.
- Apply a lot of solder to the thermal pad on the board, putting just enough to keep the top surface relatively flat.
- Clean both board and chip thermal pads with some isopropyl alcohol. Reflux.
- Place chip onto board. While holding onto the chip with one hand, clamp down on the chip using alligator clips.
- Clamp the other side. You’ll notice that the chip probably doesn’t lie perfectly flat on the board, since we put solder onto the thermal pad. This is okay and actually desirable.
- Flip the PCB upside down. Apply soldering iron to the thermal pad on the backside of the PCB, at around 650F. Keep the iron on the pad for a few seconds after all the solder starts melting.
- Give the chip a little bit to cool down, then remove the alligator clips. It should be firmly attached to the board.
- Now apply lots of flux to the leads and touch a lightly tinned iron to the leads. You won’t get any shorts if you don’t apply too much solder.