Diurnal Reef Controller for Lighting and Tides

I just uploaded a pdf of work to date, including various random bits of design and analysis.  I have a working prototype using a Raspberry PI3

It is in the "FILES" section of this project:  "new diurnal light".

The prototype PCB's got here from China:

..
for the topside ....

here is the backside:

... not bad for $8.00 (for 5 boards) ... populating the board with the voltage regulators now.

I promised information on my 3 LED prototype:

3 50 watt LEDs (each the radiantly equivalent to a 350 incandescent)  3x350=1,050 W)
and here is the backside/upside:

It has worked for some months ... used it for hydroponic tomatoes for a while (they loved it!)

I've built and I am using some of these LED's in my reef tank setup.  Most notably, I have a rigged a 50W broadband (chlorophyll absorption friendly) LED over the refugium  of my 55 gal tank.  It's been running about 12 hours every night for the last 6 months:

This LED uses 115 VAC.  The refugium grows chaetomorpha to reduce nitrates and phosphates in the tank.

I also have  a three-50W LED prototype that runs on 36VDC over another tank (2 cool white's with a broadband in the middle).  I'll post images of that soon.

Using a chart from Wikipedia (link here), I created the following chart in order to get some equivalency between bulbs and LED illumination:

The wiki chart only goes up to 300 W (incandescent), so I curve fit the data to get some idea of higher values.   Since the polynomial curve fits show a round off beyond 300, I use the linear fit.  According to that, a 50 Watt LED produces the same radiant power as a 350 Watt incandescent bulb – that should be 106 W for compact fluorescent bulbs. Of course, only the linear curve fit gets to 50W ….

ordered proto pcb's from china ... 5 boards, as described previously, 2-sided, delivery in 14-18 days ... LESS THAN $8 !

oh, here is the look up table for the normalized diurnal insolation curve:

The PCB we make will control the current with 8 bits, use a PIC24F16KA controller, and a MCP7940 real time clock.

The PIC talks to the RTC over SDA & SCL lines using I2C.  Power input (P1) comes from a 36VDC LED driver that plugs into 115 VAC.  Voltage regulators down-shift the 36 V to 12V (for the cooling fan) and ultimately Vcc (which is 3.3 V).  You see all eight current control MOSFETs, and there is a single mosfet controlling the fan speed.

The diurnal curve previously shown is programed into the PIC's memory as a list of 8-bit integers (from 0 to 255 representing a normalized insolation of 0 - 1.0).  The two-sided PCB is 59mm x 47mm.

A five-pin header is provided (P2) for programming the PIC.

This should be sufficient to prove that the concept works.

Next, I intend to add an I2C flash memory to the bus.

Then add control for a blue LED (for lunar).

Then, USB ...

Then, Bluetooth, so one board can control many.

The first cut design of a PCB to control the 50W LED by digital current control is complete.  Making Gerbers now.  8-bit control gives 256 levels of brightness from the LED.

It is important when making lights for biological systems to use CURRENT CONTROL ... not voltage/PWM.  An LED controled by a PWM signal only APPEARS to brighten or dim.  It's not really ... it's just fast blinking all on/all off .  The strobing effect is undesirable by lots of plants and animals.  On the AVERAGE, the PWM signal looks analog, but it's really just strobing digital.

I arrange eight mosfets in parallel - each controlling 1/2 the current of its most-significant neighbor, and twice the crrent of its least-significant neighbor.  The most current is controlled by the most-significant bit in the control word/byte. 

To control the 50W LED, the most-significant MOSFET turns 25W on or off (b7).  Then next MSb turns 12.5 W on/off (b6), then 6.25 W, then 3.125 W ... etc etc.

control bit               power controlled

7                                    25 W

6                                    12.5 W

5                                     6.25 W

4                                     3.125 W

3                                     1.5625 W

2                                     781 mW

1                                      390 mW

0                                     195 mW

Voltage is a constant 36 VDC, regardless of current.

Power level on each MOSFET is controlled by a current limiting resistor on the drain.  The sources of ALL MOSFETS are tied straight to the anode of the 50 W LED.

50W/36V=1.4 Amps

36V / 1.4 Amps = 27.5 Ohms resistor on the most-significant MOSFET (a high power beastie, I put two 55 Ohm 12Watt R's there in parallel)

Number 2 MOSFET requires 55 ohms

Number 3 MOSFET:  110 ohms

#4:  220 ...

... you see the trend, I think