10/03/2019 at 17:27 •
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".
07/01/2019 at 16:59 •
The prototype PCB's got here from China:
for the topside ....
here is the backside:
06/21/2019 at 21:13 •
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:
06/18/2019 at 15:21 •
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.
06/17/2019 at 15:18 •
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 ….
06/12/2019 at 20:57 •
ordered proto pcb's from china ... 5 boards, as described previously, 2-sided, delivery in 14-18 days ... LESS THAN $8 !
06/12/2019 at 15:20 •
oh, here is the look up table for the normalized diurnal insolation curve:
06/10/2019 at 17:21 •
The PCB we make will control the current with 8 bits, use a PIC24F16KA controller, and a MCP7940 real time clock.
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.
06/07/2019 at 21:24 •
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.
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