I am going for 32 LEDS but I may change my mind. It depends really on the size and spacing achievable as well as current draw and voltage drop. Lets see what works first.
I'm confident I could design this PCB straight away but it is always a good idea to read through the datasheet and do some calculations...there may be something critical I have missed or didn't know. I've used neopixel tape several times but I've never really bothered to read up on their technical aspects.
The datasheet isn't the worst I've looked at but it isn't the best either...
After some reading...and some more reading here is what I have found:
The package contains 3x LEDS and a control circuit. According to the research the control circuit draws 8 mA with all the LEDS not active (Off).
The Red LED draws 13 mA when fully on.
The blue LED and green LEDS also draws 13 mA when fully on.
Therefore each pixel (3x LEDS in one package) draws 60 mA.
If we have 32 pixels our current draw with each LED fully on (White colour) will be:
So if the calculations are correct...then we need to account for this 1.6 Amp current draw on our PCB layout. Our connector and wiring also need to handle 1.6 Amps - I'm going to design for 2 Amps to provide a little margin.
Here is the circuit diagram:
NeoPixel Lamp Schematic
Next we need to design a PCB layout. I'm going for a circular PCB which will fit behind the 84 mm polycarbonate cover. Lets set the diameter of the PCB to 80 mm - that way I know it will fit with room to spare. I will need a mounting option too...not worked that out yet! I suspect some stand offs and attached to the cover will work fine.
Here is the PCB layout:
NeoPixel Lamp Top Layer - PCB Render
NeoPixel Lamp Bottom Layer - PCB Render
I added an extra pixel in the centre of the PCB as there was room. I also added some mounting holes which weren't on the schematic. The layout went quite well and only took me a couple of hours...must be getting better at this although it isn't because of practice! I did have a nights sleep between the hours...maybe that helped...
I have exported the gerber files...next job is to get a quote from JLPCB and then assuming the price is right get some boards made. I'm going to go with black silkscreen.
In a previous post (nearly a year ago!) I mentioned I was going to design an Arduino shield to allow DMX control to Neopixels. I actually did design a board but never wrote a blog post about it. Here is where I rectify that.
I decided to design my own DMX shield for the Arduino R3 as although there are commercial off the shelf versions available they don't have electrical isolation between the RS485 transceiver and the IO (Input Output) ports. This can be quite critical when connecting up DMX lamps as some of them are not well designed and lets just say ground loops and cheap DMX lamps becoming live when they shouldn't and releasing of magic smoke and electric shocks being a very real and present danger...don't ask me how I know...
The circuit itself is pretty much the same as those already available. It has opto-coupling present on the IO, the power supply and has DIP switches on board to set the DMX start address.
Here is the circuit diagram:
DMX to SPI Converter Shield
I suppose I had better explain the circuit - This is as much for me as for the casual reader...I'll be honest I haven't looked at this for a year and some decisions taken were odd to me at first...
12 V dc input to 5 Vdc out circuit (Switch-mode)
The circuit section shows the 12 V dc input coming from the connector J1 going to C1 (100 nF) - this is a filter capacitor. Then a DC to DC converter module is present. Three 100 nF capacitors are then present to filter the output of the DC to DC converter. These switching converters are known to often cause electromagnetic interference. The capacitors are present to try to mitigate those issues.
The switching converter (PS1) used is a TRACO TEA_1-505 and it's datasheet is here:
The next section is the opto-coupled RS485 (DMX)section:
The serial and control signals from the Arduino R3 are connected to Jumpers (JP1 to JP4). This allows the user to isolate the connections from the serial pins of the Arduino R3 to allow for code upload and control of whether the DMX device will be active (in control of the DMX network and sending data packets) or passive (receiving Data packets).
I'm going to discuss each opto-coupler in turn to simplify things:
Resistor R1 (4.7 kΩ) is connected to output of Opto-coupler U1 and is present to current limit the signal presented to the serial input RX of the Arduino R3 (or clone). Resistor R6 (470 Ω) is present to current limit the signal presented to the input of U1 coming from the RO output of the RS485 transceiver (U4 - MAX 481E).
Resistor R2 (470Ω) is connected to the input of Opto-coupler U2 and is present to current limit the signal presented to the internal diode of the device. The output is current limited by resistor R4 (4.7 kΩ) and is connected to the DE and RE (inverted) inputs of the RS485 transceiver (U4 - MAX 481E).
Resistor R3 (470Ω) is connected to the input of Opto-coupler U2 and is present to current limit the signal presented to the internal diode of the device. The output is current limited by resistor R5 (4.7 kΩ) and is connected to the DE and RE (inverted) inputs of the RS485 transceiver (U4 - MAX 481E).
The Opto-Couplers are powered by 5 V dc coming from the regulated Arduino R3 supply and are isolated from the 5 V dc signal coming from the DC to DC converter
The IO (A and B) signals of the R485 transceiver (U4 - MAX 481E) are connected to three resistors (R7 - 562 Ω, R8 - 133 Ω, and R9 - 562 Ω). These are present to provide the 120 Ω impedance matching for the RS485 transceiver. The input and output to the RS485 transceiver are connected to screw terminals with an isolated return (GND2). These will connect to the signal cable used to connect this circuit to the DMX controller.
The next section is present to allow the user to pre-set the DMX address:
The 8 way DIP switches (SW1) are connected to the Arduino R3 spare pins and 330 pull up resistors. It is a standard way of connecting switches to microcontroller input pins. The current presented to the microcontroller inputs when the switch is closed is 15 mA which is within the specification of the device (ATMEL 328).
The SPI output of the circuit is taken from Pin 12 of the Arduino R3 along with supply voltage and ground to a three terminal screw connector. This is a nice robust way of connecting to off the shelf Neopixel circuits.
The final section is the standard layout used for connecting a shield circuit board to an Arduino R3.
It saves time designing PCB layouts as all of the dimensions and connections are present and contain NET labels.
Here is the bill of materials in case it is needed:
I haven't ordered any of these parts yet but I already know that some are not in stock...the fallout from the pandemic is very real. Some are due in next week so I can get ordering!
Here is the PCB layout:
The 3D render is probably easier to see and understand:
The DMX to SPI Converter shield - Top Layer
The DMX to SPI Converter shield - Bottom Layer
There isn't much to say about the PCB layout. I've tried to make sure that all of the traces carrying high current are nice and thick. The silk screen labels are visible and it is fairly easy to populate by hand if required. I wish I had labelled in the inputs and outputs so I know where the GND and +12 V input connections are and where the DMX and NeoPixel connections are. There are always things I would do differently if given a chance to repeat.
I got ten boards made by PCBWay for a reasonable price and they were delivered in very short order!
Here is a picture of the unpopulated board:
My plan is to populate and test this board as soon as possible as I intend to use it in my next project - the DMX controlled patio lamp :)
That is all for now - take care always - Langster!
A friend of mine has approached me to make him some Patio lights. He wants them to be interactive! I'm thinking the best idea would be to make him some sort of DMX controlled light with WS2815 LEDS. I can build on the previous design work I have already done which should save me some time.
For the enclosure my plan is to take an existing garden rock lamp and re-engineer it for this purpose. This should save me having to design some clever aesthetics.
To that end I have bought a cheap (£3.20) garden lamp from B & Q - A popular Home / garden improvement chain in the UK:
The lamp housing appears to made of some sort of ABS moulded plastic. The Reflector and LEDS are protected by a simple circular polycarbonate shield. There is a battery housing and a button on the base of the housing.
Don't turn it on - Take it apart!!!
The deconstructed lamp
The light actually came apart very easily...it was mainly hot glued together! The reflector, battery box and solar panel will be discarded as they won't have any purpose in the upcycled lamp. I will probably leave the solar panel on as getting it off will be difficult and it won't do any harm.
There is ample space inside the lamp for a couple of circuit boards and some ballast (weight) to stop the lamp moving too easily. My current thinking is to design two circuit boards. One for the DMX and one for the lighting. The controller will be a small microcontroller board which accepts DMX and outputs SPI to the lighting board. The lighting board will be a circular PCB with WS2815 LEDS arranged in a sensible pattern. If I'm luck it will be possible to fit 32 LED pixels on the display board.
I have not decided which microcontroller to use yet...probably an arduino or teensy variant. There is no need to go for a wifi enabled micro as the plan is to use wire to carry both power and the DMX signal.
The diameter of the reflector is 84 mm. I think the lamp PCB will need to be the same dimensions. Hopefully we can get 32 W2815 LEDS (Pixels) to fit!
So to recap our electronic and mechanical requirements:
Design a lamp PCB with 32 pixels. I think powering the lights via 12 volts might be a good idea however I will consider this more once I get to the PCB layout. We will need to ensure the tracks are suitably rated for the current flow. We will fuse the voltage signal on the control board with a user changeable fuse.
Nice to haves: 32 pixels - allows for simple channel assignment via DMX controllers. Each lamp on one universe...with 96 channels.
So the design tasks so far:
Design a Lamp PCB
Design a DMX to neopixel PCB with optocoupled DMX in and out ports - possibly using the one I've already designed.
The micro is yet to be decided.
The circuit will also be powered via 12 V dc but we will probably need to regulate that down to 5 V dc for the micro and other circuitry...sound detection, light detection etc.
I haven't got a budget set however cheaper is always better!
I've been playing about with RS485 and DMX for some time now. I am particularly interested in being able to control NeoPixels via DMX. The amount of software and experience available for using DMX to control lights and LEDS in particular is vast. YouTube is full of lighting shows and displays which range from humble but functional to truly epic and vast. Here are a couple of videos which I thought were amazing:
Submergence - Squidsoup
Tom Betgeorge's Excellent 2020 Christmas Light Show
I must admit I watched all 35 minutes of that Christmas Show...It is incredible work. Any way this is achieved is by controlling lots of LEDS in pre-programmed sequences using DMX control software and LED lights. DMX is a lighting protocol based upon RS485. Here is a brief primer on DMX:
So basically lighting technicians control the lights in theatres, discos and concerts using the DMX protocol to control the brightness, colour and state (off/on) of a light or lighting fixture (many lights in one package).
DMX uses RS485 which is a differential serial protocol that electronic equipment has been using for communication since the standard was approved in 1998 and probably earlier than that.
I'm not going to go into too much detail on R485 or DMX for now other than to say it's very useful stuff for electronics and lighting fans to know about.
I have a confession to make: I'd like to be able to control lights...not just one or two but many. If I had my way every light in my house would be sequenced and remote controlled. Unfortunately not everyone I live with approves of this plan and as such most of my lights are still just regular lights....(boring!!!).
I have been asked in the past to assist with light shows and recently I have been asked to assist with the technical development of a light show using NeoPixels.
To that end I started to look at the DMX shields available for the Arduino and have a play. I noticed that most of them have a flaw - they aren't isolated...that means that the electrical supply used to power the lights is also connected via the return (or ground) to the controller. In most cases this isn't an issue but it can be in very large lighting displays with lots of wiring and fixtures because of something referred to as a 'ground loop'.
There is nothing functionally wrong with them and I bought two of the Concineptics variants to play with. They arrived in good order and worked as described once I understood the code and the jumper settings.
In order to actually use DMX properly with the software one needs a controller. Something I was aware of but not completely in understanding of at all. I'd always used a hardware controller in the past.
So to really make use of DMX you will either need to make your own controller or buy one off Ebay or Amazon or wherever you might wish to. I wanted to use an external computer and software to control my lights as I don't own or have access to a hardware DMX controller.
I bought a USB to RS485 dongle off Amazon which works perfectly...It didn't at first but that's because I cannot wire things up for love nor money sometimes. I then bought a USB to DMX dongle and that worked straight out of the box without any issues whatsoever! Don't tell anyone but I'm very disappointed in my engineering abilities sometimes...Not being able to wire up simple circuits competently is worrisome for somebody who works in electronic engineering!
Here are the two devices I bought which I heartily recommend:
Once you have a method of controlling DMX lights it's time to either buy some or make some...user's choice. I was trying to make some so I got hold of some NeoPixel Tape and then connected everything up.
Before doing anything I tend to do some research...Planning is everything so they say....I watched several videos on YouTube and read some blogs on DMX and in particular this one stood out:
Gadget Reboot has an excellent channel and I recommend subscribing!
In it the narrator discusses exactly what I'm trying to achieve and provides all of the equipment required and some code. The only issue I had was that it didn't work for me! I didn't have the exact same setup and tried to rush things...never a good situation. Their setup uses an Arduino mega and some potentiometers, an RS485 breakout module, Buttons and some wire for the connections - for the hardware controller. For the receiver they use an Arduino uno and an RS485 breakout and some WS2812B LEDS. I suspect armed with what I know now I could probably get this setup working...
Suitable connection wire for making the connections between the arduino and the breakouts etc as well as some 4 core 120 Ohm signal cable for the RS485 communications. For testing any wire would do but once something longer distance or more permanent is required get proper cable. Belden 9842 is a pretty good option. At a pinch some old ethernet cable would work...cut the R45 connectors off and use four of the cores...
The actual setup!
You will need to flash the following arduino code onto your Arduino R3:
// Target Hardware: Arduino Uno#include <DMXSerial.h>#include "ws2812.h" // a specific LED controller that disables interrupts to work better#define NUM_LEDS 30 // number of RGB LEDs on strip - 3 LEDS in one W2182B9#define DMXSTART 1 // first DMX channel#define DMXLENGTH (NUM_LEDS*3) // number of DMX channels used (3*30 LEDs)voidsetup () {
DMXSerial.init(DMXProbe); // initialize DMX bus in manual access mode
DMXSerial.maxChannel(DMXLENGTH); // "onUpdate" will be called when all new ch data has arrived
setupNeopixel(); // setup the LED output hardcoded to pin 12 in ws2812.h
}
voidloop() {
// wait for an incomming DMX packet and write// the RGB data for 60 LEDs on the stripif (DMXSerial.receive()) {
updateNeopixel(DMXSerial.getBuffer() + DMXSTART, NUM_LEDS);
}
}
You will need to download a copy of the DMXSerial Library. It is available here:
Here is the source for ws2812.h - Cut and paste it into a text file called ws2812.h and store it in the same directory as your arduino sketch.
// neopixel.h/* The Neopixel driving routines are taken from the article and sketch from bigjosh http://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/ where the interrupt cli() and sei() are included in the sendBit function. At the sources from his github this is not the case but it's important for the usage with DMXSerial library. (see https://github.com/bigjosh/SimpleNeoPixelDemo ) These routines fit very good to the DMXSerial implementation because they switch on and off the Interrupt On DMX usual channels are used in the red then green then blue order. Neopixel wants colors in green then red then blue order so the 2 channels are switched.*/// ----- global defines from josh: -----// These values are for the pin that connects to the Data Input pin on the LED strip. They correspond to...#define PIXEL_PORT PORTB // Port of the pin the pixels are connected to#define PIXEL_DDR DDRB // Port of the pin the pixels are connected to#define PIXEL_BIT 4 // Bit of the pin the pixels are connected to// This re3sults in the following Arduino Pins:// Arduino Yun: Digital Pin 8// DueMilinove/UNO: Digital Pin 12// Arduino Mega PWM Pin 4// You'll need to look up the port/bit combination for other boards.// Note that you could also include the DigitalWriteFast header file to not need to to this lookup.// These are the timing constraints taken mostly from the WS2812 datasheets// These are chosen to be conservative and avoid problems rather than for maximum throughput#define T1H 900 // Width of a 1 bit in ns#define T1L 600 // Width of a 1 bit in ns#define T0H 400 // Width of a 0 bit in ns#define T0L 900 // Width of a 0 bit in ns#define RES 6000 // Width of the low gap between bits to cause a frame to latch// Here are some convience defines for using nanoseconds specs to generate actual CPU delays#define NS_PER_SEC (1000000000L) // Note that this has to be SIGNED since we want to be able to check for negative values of derivatives#define CYCLES_PER_SEC (F_CPU)#define NS_PER_CYCLE ( NS_PER_SEC / CYCLES_PER_SEC )#define NS_TO_CYCLES(n) ( (n) / NS_PER_CYCLE )#define DELAY_CYCLES(n) ( ((n)>0) ? __builtin_avr_delay_cycles( n ) : __builtin_avr_delay_cycles( 0 ) ) // Make sure we never have a delay less than zero// Low level function with mixed in assembler code.// Actually send a bit to the string. We turn off optimizations to make sure the compile does// not reorder things and make it so the delay happens in the wrong place.inlinevoidsendBit( bool bitVal )
{
if (bitVal) { // 0 bitasmvolatile (
"sbi %[port], %[bit] \n\t"// Set the output bit".rept %[onCycles] \n\t"// Execute NOPs to delay exactly the specified number of cycles"nop \n\t"".endr \n\t""cbi %[port], %[bit] \n\t"// Clear the output bit".rept %[offCycles] \n\t"// Execute NOPs to delay exactly the specified number of cycles"nop \n\t"".endr \n\t"
::
[port] "I" (_SFR_IO_ADDR(PIXEL_PORT)),
[bit] "I" (PIXEL_BIT),
[onCycles] "I" (NS_TO_CYCLES(T1H) - 2), // 1-bit width less overhead for the actual bit setting, note that this delay could be longer and everything would still work
[offCycles] "I" (NS_TO_CYCLES(T1L) - 2) // Minimum interbit delay. Note that we probably don't need this at all since the loop overhead will be enough, but here for correctness
);
} else { // 1 bit// **************************************************************************// This line is really the only tight goldilocks timing in the whole program!// **************************************************************************asmvolatile (
"sbi %[port], %[bit] \n\t"// Set the output bit".rept %[onCycles] \n\t"// Now timing actually matters. The 0-bit must be long enough to be detected but not too long or it will be a 1-bit"nop \n\t"// Execute NOPs to delay exactly the specified number of cycles".endr \n\t""cbi %[port], %[bit] \n\t"// Clear the output bit".rept %[offCycles] \n\t"// Execute NOPs to delay exactly the specified number of cycles"nop \n\t"".endr \n\t"
::
[port] "I" (_SFR_IO_ADDR(PIXEL_PORT)),
[bit] "I" (PIXEL_BIT),
[onCycles] "I" (NS_TO_CYCLES(T0H) - 2),
[offCycles] "I" (NS_TO_CYCLES(T0L) - 2)
);
} // if// Note that the inter-bit gap can be as long as you want as long as it doesn't exceed the 5us reset timeout (which is A long time)// Here I have been generous and not tried to squeeze the gap tight but instead erred on the side of lots of extra time.// This has thenice side effect of avoid glitches on very long strings becuase
} // sendBit()// Neopixel wants bit in highest-to-lowest order// so send highest bit (bit #7 in an 8-bit byte since they start at 0)inlinevoidsendByte(uint8_t byte)
{
for (uint8_t bit = 0; bit < 8; bit++) {
sendBit(byte & 0x80);
byte <<=
1; // and then shift left so bit 6 moves into 7, 5 moves into 6, etc
} // for
} // sendByte()/* The following three functions are the public API: ledSetup() - set up the pin that is connected to the string. Call once at the begining of the program. sendPixel( r g , b ) - send a single pixel to the string. Call this once for each pixel in a frame. show() - show the recently sent pixel on the LEDs . Call once per frame.*/// Set the specified pin up as digital outvoidsendPixel(uint8_t r, uint8_t g, uint8_t b) {
sendByte(g); // Neopixel wants colors in green then red then blue order
sendByte(r);
sendByte(b);
} // sendPixel// ----- defines and routines from josh - End -----voidsetupNeopixel() {
bitSet( PIXEL_DDR , PIXEL_BIT );
} // setupNeopixel()// read data from the DMX buffer (RGB) and send it to the neopixels...voidupdateNeopixel(uint8_t *ptr, uint8_t pixels) {
uint8_t r, g, b;
// no interrupt is welcome.
cli();
for (int p = 0; p < pixels; p++ ) {
r = *ptr++;
g = *ptr++;
b = *ptr++;
// send to Neopixels// sendPixel(r, g , b);
sendPixel(r >> 2, g >> 2, b >> 2);
} // for// interrupt may come.
sei();
// Just wait long enough without sending any bots to cause the pixels to latch and display the last sent frame
_delay_us((RES / 1000UL) + 1);
} // updateNeopixel()// End
Once you have everything setup you will need to download some DMX software. There is a great deal to choose from. Some of it is very complicated and expensive and some are open source, still complicated but free for fair use.
I chose to use Q Light Controller Plus. I have heard good things about Xlight and JinX.
You can down load Q Light Controller Plus from here:
Once installed on the operating system of your choice, load up the software:
You will be presented with the following screen:
Click on the Inputs/Outputs button in the bottom middle of the screen.
Ensure that DMX USB is selected and that it relates to the USB Dongle. It was already selected for me.
Next it is time to add a fixture. Click on the fixtures icon in the bottom left corner. You will be presented with the following screen:
Click on the green '+' Icon in the top left corner to add a DMX controlled lighting fixture.
I called mine 'LED_strip' but yours can be anything you wish. I chose 90 channels as that is what was set in the code and I have 30 NeoPixels on my strip. Each colour = one channel. I noticed that Q Light Plus can only control 99 channels in one universe...Start from address 1 as there is only one fixture and therefore quantity = 1 and address gap = 0.
Anyway...Click OK and then Click on the Simple Desk button in the bottom middle of the screen. The following window will be presented:
Now we are getting somewhere! If you look at the display it looks quite like an audio mixing desk and in a way it is...just for lights...If you increase the slider on channel 1 you should see your first LED light up and it will be RED. If you were to increase channel 2 It would light up up the GREEN LED in the first NeoPixel. Channel 3 = BLUE LED etc. The big red slider at the left hand side of the screen controls the master brightness.
Here is what I did to quickly test things:
It gives the following responses on the LED strip:
That is about as much as I currently know on how to control Q Light Plus! There are a million tutorials available however and a very active forum. Go check them out!
I also had a quick play with JinX which can be downloaded from here:
I'm not going to go into how it works as the manual is OK but here is a quick video showing it in action:
That's all for now. The next post will be about how I designed an isolated DMX shield and go into how the code works and probably a bit more on how to use DMX software. I need to research more into the software and setting up scenes etc.
