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Author Archive | Paul Badger

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!

Summary:

  • 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.

Wires, more wires, in all gender combinations

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These are 12″ long ribbon-wire jumper cables suitable for a wide variety of temporary or permanent wiring tasks. These are much more robust than flexible breadboard wires which are fine for quick prototypes, but do not hold up to soldering.

We’re even including some double-long male headers with the female pins, as handy gender changers.

They’re in the shop and ready to go.
I’m giving away ten of ten of them for free. Use coupon code RIBBON_WIRES. Limited to one per person on orders over $10.