- RFM12B Board
The RFM12B Board is a compact breakout board for HopeRF's RFM12B radio module.
The board works with a whole range of Arduino (compatible) boards. For ease of use, the header pins are labeled with signal names as well as Arduino pin numbers.
The supply voltage (Vdd) for normal operations of the RFM12B radio module is limited to 3.8V. When connecting to a 5V context (e.g. Duemilanove), there is provision for a voltage regulator circuit and voltage level converters for the signal pins.
An antenna must be connected to the module - see the discussion below.
See the RF12 library for source code and examples.
For use at 5V:
- Include all the components (C1, C2, C3, VR, R1, R2, R3, R4, R5, R6) to activate the signal voltage-level converters and the voltage regulator (VR).
The VR reduces the 5V supply to 3.3V for the RFM12B module. A regulated 3.3V output is available from the connector pin marked '3V3' for light loads from other circuits needing 3.3V.
For use at 3.3V: (the signal logic levels and the power supply voltage level already match)
- Omit R4, R5, R6. Omit R1, R2, R3 and bridge across the respective topside solder jumpers SJ1, SJ2, SJ3. This disables the voltage-level converters.
- Omit the voltage regulator (VR) and supply 3.3V into the connector pin marked '3V3'.
- Insert C2, C3 to improve decoupling of the 3.3V supply.
Dimensions: 21.1 x 38 mm
CadSoft EAGLE design files: see below.
Construction hints - RFM12B module¶
You will see in the picture below that some RFM12B module pins are left unsoldered. This is because those pins are for signals that are not used in this design. For example, the module can output a clock signal to be used with an MPU lacking its own clock generator - that does not apply here. If you look at the zoomed false-color snapshot below, only pads with red traces need soldering (hard to see but this includes ANT and GND). If you want to count the pins carefully, then this method is fine. But soldering them all is fine as well.
An antenna 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 only when adjustment is complete.
Without access to some measurement system, simply trim to the length for the corresponding Band entry shown 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 about one wavelength 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 white insulation that is practical.
How to Get It¶
Related Weblog Posts¶
- 2011-02-02 - Meet the RFM12B Board