Table of contents
RFzero specifications
| Characteristics | Value | Notes |
|---|---|---|
| Voltage | 5 V | Voltage on JP1. On the USB connector the max voltage is 5 V. Absolute max voltage is 9 V for shorter periods |
| Current | 70 mA, 1) 110 mA, 2) 500 mA, 3) | 1) No LCD or GPS antenna connected. Program with empty setup and loop 2) Beacon program with LCD and GPS antenna connected 3) Maximum total current |
| Supply connector | 2 pin terminal block | Ø1 mm wire |
| GPS connector | SMA female | 3,3 V DC to GPS pre-amp. Optional GPS USB connection on bottom side |
| Frequency range | 2289 Hz to 200 MHz | Above 200 MHz is outside the Skyworks specification. However, many Si5351A will work beyond 290 MHz. |
| RF power | 13 dBm | 400 kHz to 200 MHz |
| RF clock | 27 MHz, 10 PPM | Short term stability less than 105 mHz and less than 13 mHz with foam cover |
| RF connector | SMA female | |
| USB connector | USB female | v.1.x: USB B, v.2.x: USB C |
| Micro controller | ATSAMD21G18 | 32 bit ARM Cortex M0+ |
| MCU clock | 48 MHz, 10 PPM | |
| Flash memory | 256 kB | |
| EEPROM | 8 kB, v.2.x 1 kB, v.1.x | Optional EEPROM in 8 pin DIP socket using the same I2C address 0x50 Changeable. 8 pin DIP in socket |
| DC current per I/O pin | 7 mA | |
| MCU connector | 10 pin Cortex | 2 x 5 pin 50 mil connector |
| Analog inputs | 8 | 12 bits |
| Analog output | 1 | 10 bits |
| Digital I/Os | 28 | Hereof up to eight can be analog |
| Driver | ULN2803A | 8 bit Darlington array 50 V and 500 mA. In socket for easy replacement |
| PWM pins | 16 | Pins D0-D11 and A2-A5 on TCC0/1/2 and TC3 |
| I2C, SPI and UART ports | 3, 4, 4 | SERCOM ports |
| LCD connector | SIL 12 pin 2,54 male | Pin 1-6 to LCD pin 1-6 (VSS-E), and pin 7-12 to LCD pin 11-16 (DB4-Cathode) Not factory mounted |
| LCD voltage jumper¹ | SIL 3 pin 2,54 male | 3,3 V or VI that is about 0,5 V below the supply connector or USB voltage whichever is highest. Not factory mounted |
| Headers | SIL 2,54 mm male | Not factory mounted |
| Ground loop | Ø1,5 mm cobber wire | Not factory mounted |
| LEDs | 3 mm | The four 3 mm LEDs are not factory mounted. One on-board Test LED |
| Size | 99,5 mm x 79 mm | Half Eurocard PCB. Fits into a standard metal sheet box (Weissblechgehäuse) 102 mm x 82 mm x 30 mm for optimum RF shielding |
| Weight | 30 g |
¹: The LCD can be supplied either by 3,3 V or VI using the JP13 jumper. But the control and data lines are always 3,3 V logic. Different contrast and backlight values apply. The backlight can be increased by adding a blob of solder to the SJ1 solder joint shorting the R16 backlight resistor.
The reason for not factory mounting the LEDs and headers is to allow for individual configuration e.g. mounting the LEDs through a front plate and only install the relevant jumpers/headers.
LEDs
You can choose to mount the 3 mm LEDs directly on the RFzero board straight up or bent so they fit through holes in a front plate. You may even mount a 2 pin header per LED, and run wires to the front plate further away.
All the LEDs have to be connected/mounted correctly. On the RFzero the positive side of the LEDs (the anode is the long terminal) have to be mounted to the left on the board when the USB connector faces you. There is also a small plus sign “+” printed on the board. If you mount the LEDs the wrong way they will not light up. So please remember this phrase: Long Leg Left.
You may verify if your intended way to solder the LED in place is correct by putting the LED terminals through the holes, but without soldering them, and connect power to the RFzero. Then gently, using a finger, apply force to the LED terminals to make sure that there are physical contacts between the terminals and the holes in the PCB. If the LED is lit then you have connected the LED in the right way.
Examples of mounting the LEDs where the PPS LED is connected through a pair of wires to a two pin header instead of directly on the board.
If you are in doubt, after soldering the LEDs to the board, you can easily verify if you did it in the right way. If you look closely at the LEDs you will be able to see if the big part of the internal of the LED, the cathode, is to the right. You can see this clearly in the green LED in the picture above.
LCD connections
The RFzero can use both 3,3 V and 5 V liquid crystal displays (LCD), but, if using a 5 V LCD the logic communication has to work on 3,3 V level. Most modern 5 V LCDs are able to do this but if you have an old 5 V LCD it may not work. If you are to buy a new LCD please ask the seller specifically for a 3,3 V LCD.
RFzero, and Arduino in general, supports LCDs that are compatible with the Hitachi HD44780 specification. You can use other standards but in this case you may have to find a third party display library or write it yourself.
The RFzero supports other displays than the HD44780 in parallel mode. Please see the displays page for more information.
LCD voltage jumper
Before you connect any LCD to the LCD header please ensure you have set the correct drive voltage for the LCD on the LCD voltage select header – JP13. Alternatively, if you know that you will always be using one of the voltages you could short the relevant jumper position with a small piece of wire that is soldered in place.
The LCD voltage header JP13.
The LCD voltage set to use VI
Please note that if you run the LCD on the VI level the contrast and backlight will change if the VI is changed.
The LCD voltage set to use 3,3 V (3V3).
LCD header and connections
The RFzero LCD header JP12 is prepared for LCDs that comply with the Hitachi HD44780 specification. Using two cables with six wires in each you can easily connect the LCD to the RFzero board. One cable should go to the left side of JP12 (GND, V LCD, CON, RS, R/W and ENA) and the other cable to the right side of JP12 (DB4, DB5, DB6, DB7, Anode and Cathode).
The LCD header JP12.
On the backside of the LCD connect the two cables to “each end” of the 16 pads/pin header leaving the four in the middle unused.
Two six wire cables connected to a LCD pins 1-6 and 11-16.
The RFzero LCD header is designed to run the LCD in four bits mode, i.e. LCD data on DB7 to DB4. If you need to run your LCD in eight bits mode you will have to take the remainder four bits from some of the other pins available on the RFzero and connect them to the DB3 to DB0 pins on the LCD.
LCD contrast and backlight
The contrast of the LCD can be controlled on the R15 trimmer. Please note that if you run the LCD on the VI level the contrast will change if VI is changed.
If you think that the backlight is not strong enough for the place where you will use your RFzero you can add a blob of solder to the SJ1 solder jumper. Doing so shorts R16 so the backlight resistor goes from 20 Ω to 10 Ω allowing more current to the LCD.
The R15 LCD contrast trimmer and SJ1 solder jumper.
Please note that if you run the LCD on the VI level the backlight will change if the input voltage is changed.
GPS back-up
You have the possibility to connect a back-up battery or supercapacitor to the RFzero (does not apply to PCB v1.0). If you don’t want to back-up the GPS almanac it is a good idea to short JP7-1 (+/VB+) and JP7-2 (VB) using the supplied header and jumper.
Having the GPS backed-up may result in slightly faster satellite acquisition, thus valid GPS data. However, if the GPS almanac is more than two weeks old the back-up has no practical relevance.
The JP7 header and back-up connections.
The RFzero has built-in components for charging an external supercapacitor. According to the datasheet the typically back-up current, I_BCKP, is 15 μA. Thus, a 1 F supercapacitor with an ESR of 100 mΩ should provide about 15 hours of back-up time.
The below table shows how to connect the jumpers vs. back-up type.
| Back-up type | JP7-1 (+/VB+) | JP7-2 (VB) | JP7-3 (BU+) | JP7-4 (GND) |
|---|---|---|---|---|
| No back-up | Short with JP7-2 | Short with JP7-1 | Not connected | Not connected |
| Supercap. (3,0 V to 3,3 V) | Short with JP7-2 | Short with JP7-1 | Positive terminal | Negative terminal |
| Battery (3,0 V to 3,3 V) | Not connected | Not connected | Positive terminal | Negative terminal |
The GPS data out (GDO) and GPS PPS out (GPO) connections on JP7 are not used for GPS back-up purposes.
Example of a battery holder for two AA batteries, Ø14 mm x 50 mm.
GPS signals to external devices
You may be in a situation where you want other devices to receive the GPS that are received by the RFzero. For such use the GPS data out (GDO) and GPS PPS out (GPO) connections on JP7 are available.
The JP7 header showing the GDO and GPO connections.
Please note that you may have to buffer and level shift the GDO and GPS signals, before they reach the receiving device.
Debugging, test points and GPS USB
The RFzero board contains a number of test points that can be used for troubleshooting or optional access. Keep in mind that you can also use the Test LED as an aid in the software debugging.
| Name | Description | Value | Type |
|---|---|---|---|
| TP1 | VI (about 0,5 V below the supply voltage) | ~4,5 V if supplied from 5 V or USB | Analog |
| TP2 | Voltage on the digital circuit | 3,3 V | Analog |
| TP3 | Voltage on the Si5351A | 3,3 V | Analog |
| TP4 | USB DP | USB serial data | Digital |
| TP5 | USB DM | USB serial data | Digital |
| TP6 | GPS data out (TX, GDO) | Serial data | Digital |
| TP7 | GPS control data in (RX, GCI) | Serial data | Digital |
| TP8 | GPS PPS (GPO) | One pulse per second and 100 ms wide (default) | Digital |
| TP9 | GPS pre-amplifier voltage | 3,3 V | Analog |
| TP10 | I2C/Wire internal SCL | Serial data to/from the EEPROM and Si5351A | Digital |
| TP11 | I2C/Wire internal SDA | Serial data to/from the EEPROM and Si5351A | Digital |
| TP12 | Ground on bottom side of the PCB | Ground | Analog |
| TP13 | Optional GPS USB DP on the bottom side of the PCB | USB serial data to/from the GPS | Digital |
| TP14 | Optional GPS USB DM on the bottom side of the PCB | USB serial data to/from the GPS | Digital |
The TP12, TP13 and TP14 test points on the bottom side can be used to access the u-blox NEO-7 directly via an USB port, e.g. for synchronizing a PC to the GPS network. By default this optional GPS access is disabled. To enable it simply short the SJ2 solder jumper on the bottom side.
The bottom side of the PCB showing the optional GPS solder points where G = Ground, M = DM, P = DP and the SJ2 solder jumper (square pads).
Pin outs, schematic and component locations
RFzero MCU, names and board pinout
RFzero versions 1.x come with a 1 kB EEPROM in a DIP8 socket.
RFzero versions 2.x come with an 16 kB EEPROM SOT323-5 mounted on the PCB. Holes are provided for an optional EEPROM in a DIP8 socket that uses the same I2C address as the SOT323-5. Thus the factory mounted EEPROM has to be removed to use the optional EEPROM.
An on-board low/high pass filter can be designed with your favorite filter design program. If you don’t have a filter design program the free Elsie by Tonne Software Jim, W4ENE, is a highly recommended.
RFzero component locations, PCB v.2.0
RFzero component locations, PCB v.1.2
RFzero component locations, PCB v.1.1
RFzero component locations, PCB v.1.0
Shield
If you want to expand the RFzero board with your own circuit you can easily add a shield that covers the analog and digital MCU pins found on JP2: GND and VI, JP3: USB, JP4: A0-A5, JP5/JP6: D0-D7, JP10: D16-D19, JP11: D8-D15, and JP12: LCD.
The size of the shield should be slightly larger than 19 modules x 24 modules (~50 mm x ~63 mm) to make a perfect fit.
You can make your own shield from a standard Vero-board.
If you have a shield mounted on your RFzero and want to access the GPS module you can do this via JP7. You may even connect several shields by daisy chaining the GPS Data Out (GDO), GPS PPS Out (GPO) and ground (GND) from the RFzero to the shield.