Pololu’s basic relay carrier board makes it easy to incorporate a “sugar cube”-style power relay into your electronics project. An integrated MOSFET allows the relay to be controlled with a low-current digital input, and a pair of indicator LEDs show when the relay is activated. The three control pins have a 0.1″ spacing compatible with standard solderless breadboards and servo cables, and the switch pins are available for use with 5mm-pitch terminal blocks or 0.2″-spaced pins.
The Pololu basic relay carrier makes it easy to control a single-pole, double-throw (SPDT) power relay that has the common “sugar cube” pinout and footprint. This product is just the carrier board PCB assembled with all of its surface mount components, including a MOSFET for controlling the relay, indicator LEDs, and a flyback diode; it does not include a relay or connectors. This board is also available with 5 V and 12 V power relays (assembled or as a partial kit):
The carrier board routes the three relay control pins to 0.1″-spaced pins compatible with standard solderless breadboads and female servo cable connectors. The relay switch pins are routed to a set of large pads intended for use with a 3-pin 5mm-pitch terminal block and a set of smaller pads with a 0.2″ pitch, making them compatible with 0.1″ perfboards. The carrier board has four mounting holes that work with #2 or M2 screws.
Advantages over similar products
Comparison to the dual-channel version
Our basic relay carrier boards are available in single-channel and dual-channel versions. The single-relay carrier is less than half the size of the 2-channel carrier (due in part to its smaller mounting holes and lack of barrel jack footprints), so it might be more appropriate to use two single-channel boards instead of one 2-channel board in some space-constrained applications. The following table shows some of the key differences between the two versions:
Using the relay module
The switch portion of the relay is accessible on one side of the board while the control pins are routed to the other. The relay coil is powered by supplying the appropriate coil voltage for your specific relay across the VDD and GND pins, and it is activated by a digital high control signal on the EN pin. The control signal is fed directly to a BSS138 N-channel MOSFET, which in turn actuates the relay coil when the control voltage exceeds approximately 2.5 V (see BSS138 datasheet (92k pdf) for details).
The relay switch terminals COM (common), NO (normally open), and NC (normally closed) are routed on the PCB with a minimum clearance of 60 mils (1.5 mm) from other copper. The copper traces are designed to be at least 45 mil (1.1 mm) from the board edges, though manufacturing variations in the board edges can make those distances slightly lower.
In most applications, the current and voltage ratings for the module will match the ratings of the relay used. Maximum current, maximum voltage, and life expectancy are interdependent; we therefore recommend careful examination of your relay’s datasheet.
Warning: This product is not designed to or certified for any particular high-voltage safety standard. Working with voltages above 30 V can be extremely dangerous and should only be attempted by qualified individuals with appropriate equipment and protective gear.
This schematic is also available as a downloadable pdf (131k pdf).