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Author Archive | Paul Badger

RGBW COB LED driver board


We created a board for driving  RGBW COB (Chip-On-Board) LEDs. We also sourced some RGBW (red, green, blue, white) COB LEDs, and heatsinks to put together a complete LED lamp kit. The drivers are constant-current source drivers based up the same topology as a buck switching regulator, so there is very little heat generated by the drivers. The other advantages of the driver, and the reason that switching regulators have taken over the world, is that any voltage supply may be used (at or above 12V) without losing efficiency. In other words if the supply voltage is raised, the current draw at the supply is reduced while the current supplied to the LEDs will remain constant.

The COB LEDs however do get hot, and definitely need a heat sink. We put a thermistor on the board, with a voltage divider, so you can monitor the heat on the heatsink if you are using a microcontroller board.

We also sourced the COB leds and the heatsinks so we can provide this either as a complete kit or an complete assembly.

A great thing about the LED driver we found is that the LED AL8861 driver chip inputs can accept an analog input, as well as PWM, allowing you to build a nice variable color RGBW lamp with only four potentiometers. The driver board inputs work equally well with PWM outputs from an Arduino or other microcontroller, and dim easily from 0 to 100% in a nice linear curve. The driver board will accommodate either one or two COB LEDs with currents up to 600 mA.

There is also nothing to say that you couldn’t drive a whole host of other types of LEDs such as 24 or our 1 watt LEDs arranged in a 3 series x 2 parallel x 4 channels, or  120 5mm LEDs arranged in 3 series x 10 parallel x 4 channels. The mind boggles at the possibilities.

Some custom applications might include:

    • Controllable LED signage
    • Custom / DIY LED Lamps
    • Theatrical Lighting
    • Grow Lights
    • Colored Strobe Light Experiments
    • Impressive and blinding Halloween costumes

Specifications for the COB LEDs:

These are the specifications from the manufacturer for one COB LED.

Channel Volts Current Lumens
red 6-7V 350mA 200-220
green 9-11V 350mA 320-340
blue 9-11V 350mA 80-100
white 9-11V 350mA 320-340

We’ll have product links up as soon as get done editing the product pages. Also a discount code for the first few buyers.

Calibrating The Rev. P Wind Sensor From A New Regression

I reprocessed some old data to add some software temperature compensation for the Rev. P wind sensor. The sensor itself has hardware temperature calibration built in, but the hardware compensation isn’t perfect.

You can see by these trend lines in this ADCunit vs static pressure graph that the curves diverge slightly at the upper end of the graph. I used the static pressure data from a pitot tube along with humidity and temp data, to convert the pitot tube data to wind velocities. I then set up a regression and derived an equation that matched the curve of the sensor.

I did the regression, solving for the output voltage instead of the wind speed, as I probably should have done. When the regression was done I had to factor the final equation, solving for the wind speed (in MPH) instead of for the volts, which is what the sensor outputs. This resulted in slightly less clear math, than it might have been, had I done the regression the other way around. I’m far from an expert Excel jockey, but knowing how to use the “Solver” in Excel makes me feel like at least I could play one on TV, after maybe a clean up and a shave.
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33 Amp 12 Volt Power Supplies

These are 12 volt, 33 amp switching power supplies suitable for a range of high current uses. We used them for a public art installation that we were hired to engineer and install and they performed admirably for 3 months. We powered more than 200 feet of WS2812 LED strips with a couple of these power supplies.

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RFM69 Radios

New Radios!

The RFM69CW radio module by HopeRF is a compact, powerful radio transceiver module for swapping data packets in the 868 MHz ISM band, using standard and enhanced FSK modulation. The radio is great for sub-compact designs; just 4mm of mounted height from using an SMD precision crystal.

Though consuming a similar level of power, the RFM69CW receiver section can decode fainter signals than the classic RFM12B, so it has better receive sensitivity. The transmitter section *maximum* output power is +13dBm, considerably higher than the +5dBm of the RFM12B. The current drain at these (adjustable) higher power settings is correspondingly higher though. With the better receiver sensitivity, many applications will not need to use the higher transmit power settings, potentially saving on battery life.

Compared with the RFM12B, pairs of RFM69 modules will generally have greater range and/or better penetration of walls/ceiling than when using pairs of the classic RFM12B.

The physical module is compatible with the PCB footprint on all current JeeNodes and JeeLinks. For details of the fast-evolving level of software support, see this Forum topic on the JeeLabs forum.

Control is via a fast SPI bus with reduced loading on the microcontroller, another nice advantage with the radio. The recommended power supply range of 1.8 < Vdd < 3.6 V can squeeze almost the last energy out of depleting batteries without needing a boost converter.

An antenna must be connected to RFM69 module – for 868 MHz, an 82-mm (quarter wavelength) wire can be used (not included). Operation without an antenna at the higher transmitter power levels risks permanent damage to the output stages.

Marking Convention: a yellow spot on the top of the transceiver chip indicates optimized for the 868 MHz ISM band. You can have confidence that you are building your project with a fully functional module!


  • More transmit power than the RFM12B (but more current required).
  • Better sensitivity on receive.
  • An RF signal strength is available
  • Fits the current RF12B footprint
  • The JeeLabs driver fully supports the radio with only one definition change at the top of a sketch.
  • RFM69 and RFM12B radios may be mixed in a JeeNode network and talk to each other.

For detailed specifications, see HopeRF’s RFM69CW documentation.

The RFM Board provides convenient signal breakout with an option for connecting to 5V power systems.

Digital Smarties (The JeeLab Shop) stocks a 868 MHz version of these modules with EU prices. Both Modern Device and Digital Smarties (Jeelab Shop) have the 434 versions.

Right now we are selling these on RRM12B boards and JeeNode kits.