From a H/W point of view all you need to get started is to connect your RFzero via a USB cable to your computer. If you want to do a bit more you may connect a GPS antenna and mount the headers, LEDs and a display too as described below. Once you have become familiar with your RFzero you may take a look at all the H/W modifications possible.


If you later on decide to use a shield it is a good idea to mount the headers carefully and standing straight up. Otherwise you may find it difficult to mount a shield later on.


You can choose to mount the 3 mm LEDs directly on the RFzero board standing 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 experience, 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.

GPS back-up

You have the possibility to connect a back-up battery or super capacitor 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 a 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 super capacitor. According to the datasheet the typically back-up current, I_BCKP, is 15 μA. Thus, a 1 F super capacitor 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 typeJP7-1
No back-upShort with JP7-2Short with JP7-1Not connectedNot connected
Supercap. (3,0 V to 3,3 V)Short with JP7-2Short with JP7-1Positive terminalNegative terminal
Battery (3,0 V to 3,3 V)Not connectedNot connectedPositive terminalNegative 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.

Ground loop

The ground loop, JP15, to the right of the RFzero is a good signal ground, and makes it very easy to attach an alligator clip to, if you want to measure something on the RFzero.

The ground loop wire soldered in place.

To mount the wire please strip the wire supplied, and bend it using a pair of pliers. Then cut the two legs to the same length; 12 mm to 15 mm. Since the wire is rather thick, and it is to be soldered to the ground, a fair amount of heat from the soldering iron is required. The easiest way to solder the wire is to start from the top side. Then you can align it properly before soldering it from the bottom side too.