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JeeNode USB

The JeeNode USB is a low-cost combination of radio, microcontroller board, and USB interface:

Version 3
Version 5

The JeeNode USB is a JeeNode with an built-in USB interface. It has exactly the same size and has the same connectors (except FTDI) as the original JeeNode.

Differences from the original JeeNode:

  • FTDI connector is replaced by a USB plug and on-board FTDI chip
  • Two LEDs to signal RX and TX activity
  • A blue “activity” LED, connected to PB1
  • A small reset button between ports 3 and 4
  • An on-board Lithium Polymer battery charger with a “charge” LED (near the USB port)
  • The PWR pin operates at 4.2V when plugged into USB
  • Total current draw is limited to 280 mA (max LiPo charge current)
  • All compontents are surface-mounted instead of through-hole

How to Get It

Pre-assembled units and boards are available in the Shop.
Or create your own boards with these EAGLE files: see below.
Dimensions: 23.0 x 82.0 mm
Everything is provided as open source, both hardware and software.

Changes in v5

There are some minor changes from v3 in the most recent version (v5) of the board:

  • The values of some power rail (Vbus, 3.3V) capacitors changed to improve decoupling and regulation when powered from the USB port.
  • The “charge” LED is now RED (see warning note about using excessive charging times).
  • The rarely-used Vbatt/PWR voltage divider (R7,R8) is no longer populated on the board to reduce the quiescent load when running only from the lithium battery.

N.B. v4 was not produced in volume due to problems with an alternative type of the Lipo charger chip (see the Weblog reference 2013-01-26 - Bad Lipo charger chip). The shorting link across the charger chip is pre-installed, providing a 5.0V PWR - this is NOT configured to connect a LiPo.

How to Build It

There are no specific build instructions for this board other than the RFM12B module hints below.

RFM12B module hints

The antenna (Ant) is required and can be a simple 1/4-wavelength piece of wire soldered at the ANT position:

  • for 433 MHz, use a 165 mm wire
  • for 868 MHz, use a 82 mm wire
  • for 915 MHz, use a 78 mm wire

The wire supplied with the kit is a little longer to allow for trimming - simply bend a few mm. back on itself at the floating end of the wire and cut to length when adjustment is complete.

Without access to some measurement system, simply trim to the length shown for the corresponding Band entry listed above - that is close enough for most systems.

If you have access to a field strength meter, or are using the soft NRfMon-nano Spectrum Analyzer , you can adjust this temporary “shortening” for maximum effective output power (take care to not disturb the aerial position between tests for consistency - the radiation pattern is affected by all conductors within ~ 2-3 wavelengths of any part of the aerial, including hands!)

The ground (GND) connection is not required when using a simple, single wire aerial. The GND pad is reserved for when the aerial is mounted remotely through a length of co-axial cable. Solder the outer sheath of the coax here, leaving the shortest length of unshielded inner insulation that is practical.

How to Use It

With RF12demo loaded, you can turn on the blue LED with “1l” (figure 1 + lowercase L).
The opening dialog of the RF12demo describes the command set available.
There are pinout diagrams in the Pinouts section.

Lipo Charging Cautions

Note that the Lipo charging function is designed for topping up the battery from USB power for subsequent use offline. When a sketch is running, the charging current splits between the ATMega load and the battery, leading to longer charging times. In some circumstances, the end of charge determination is ambiguous, leading to either an undercharged battery or excessive LiPo “trickle” charge times. For best energy storage and battery life, charge the Lipo with the ATMega sleeping or if the ATMega is running, avoid lengthy charging times.

The target constant current charge value is set at 280mA. You can estimate the minimum charge time for an “empty” battery from the cell capacity divided by this charge current. Use a large enough battery ‘C’ rating to ensure that this charge rate does not exceed 1C. Less than 1C charging is not a problem within reasonable limits - the battery will just take proportionally longer to receive a full charge.

Do not run the Lipo battery charge level down too low (<3.0v) - this can shorten its effective life dramatically. The charging circuit will safely attempt to charge a “flat” battery by entering a low current mode until the battery voltage recovers to the normal range.

See Also

The JeeLink is a smaller version with a case. No headers, but with flash memory added.
The JeeNode is a through-hole kit variant which connects via FTDI instead of USB.

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