Source: https://mokxi.com/parts/relaydpdt Updated: 2026-11-10 Part # DPDT relay The bare relay: a coil for a transistor to drive and two poles on one arm. See every part - 8 pins - 6 settings - In 3 projects Drawn live by the editor's own code, at the size you see it. At a glance ## The DPDT relay in brief What it is, and every setting the properties panel gives it. A bare DPDT relay is the small sealed 5 V relay with no module around it: a coil (COIL1 and COIL2, either way around) and two changeover poles on one arm, COM1, NO1 and NC1 and COM2, NO2 and NC2. Its 125 ohm coil takes 40 mA at 5 V, more than a pin should source, so the pin drives a 2N2222 through 1 k, the coil sits between 5 V and the collector, and a 1N4007 goes across it, band to 5 V. On an ESP32 a 3.3 V GPIO drives the same transistor, but the coil still needs 5 V: Mokxi pulls the arm in at 75 percent of the rating, 3.75 V, so a 5 V coil on 3.3 V never closes. It lets go only under 10 percent, takes 5 ms to pull in and 4 ms to release. Two poles on one arm let one coil reverse a motor: the motor across the COMs and the supply crossed over between the NOs and NCs. The classic mistake is wiring the coil straight to a pin. Coil inductance, the kick the diode is there for, contact bounce and contact ratings are not modeled. Family Outputs Pins 8 coil_volts 5 the rated coil voltage, 5 V. coil_ohms 125 its resistance, 125 ohms, which is 40 mA at 5 V. must_operate and must_operate 0.75 must_release 0.1 the fractions of the rated voltage at which it pulls in and lets go, 0.75 and 0.1. pull_ms and pull_ms 5 release_ms 4 5 and 4 ms. Pins ## 8 pins Named as the editor names them, so a wire lands where you expect it. Pin What it does COIL1 The coil, either way around. COIL2 The coil, either way around. COM1 Pole 1: the arm, normally open, normally closed. NO1 Pole 1: the arm, normally open, normally closed. NC1 Pole 1: the arm, normally open, normally closed. COM2 Pole 2. NO2 Pole 2. NC2 Pole 2. How to use it ## How to use a bare DPDT relay with an Arduino A bare relay has nothing in front of its coil, and the coil takes 40 mA at 5 V, so it hangs between 5 V and a 2N2222’s collector. Pin 7 drives the base through 1 k, and a 1N4007 goes across the coil with its band to 5 V. digitalWrite(7, HIGH) pulls the arm in. The two poles move together but switch separate circuits. In this project pole 1 runs a DC motor (COM1 to the motor, NO1 on 5 V, NC1 on ground, so the motor brakes when released), and pole 2 lights a green LED on NO2 or a red one on NC2. Wire a motor between COM1 and COM2 with the supply crossed over between the NOs and NCs instead, and one coil reverses it. Part pin Board pin COIL1 5 V COIL2 Transistor collector COM1 Motor NO1 5 V NC1 GND COM2 5 V NO2 Green LED, through 220 ohm NC2 Red LED, through 220 ohm On an ESP32 the 3.3 V pin drives the same transistor, but keep the coil on 5 V: it needs 75 percent of its rating, 3.75 V, to pull in, so a 5 V coil on 3.3 V never closes. Click to open it in the editor This is the simulator itself, running here. Click anything to open it in the editor. Open this project in the editor Read the full tutorial How it is modeled ## What is true about the DPDT relay, here In its help article’s own words: what the simulation gets right, and where it stops. ### Modeled The coil is a real 125 ohm load, so a resistor in series or a weak supply leaves it with less than it needs. It pulls in at 75 percent of its rating and does not let go until it falls under 10 percent, so once in it holds on at a voltage that would never have pulled it in. Both poles move together, and neither contact is made while the arm travels. ### Not modeled The coil's inductance, which is what the diode is for: here the current stops instantly and nothing breaks without the diode, so the circuit is right to have one and the simulator cannot show why. Contact bounce, contact ratings, and the change of coil resistance with temperature. From DPDT relay, in full. Projects ## See the DPDT relay in a project 3 built-in projects use it. Each opens in the editor, already wired. Boards ## The boards it is shown on This board has a built-in project with the DPDT relay in it. - Arduino Uno R3 More parts ## The rest of the bench Every one of these is drawn and simulated the same way. Full-size breadboard A real 0.1 inch grid with the rails and the center channel, 63 columns wide. Jumper wires Drag from any pin or hole to any other. Corners snap, and you can drag them. Power A supply rail at the voltage you choose. Ground The other end of every circuit. LED Lights when current flows. Five colors, and the brightness is what your eye would see. Filament lamp A tungsten bulb in a holder: an inrush when it is switched on cold, tens of milliseconds to warm up, and dim on half its voltage. Resistor Any value you like, with the color bands drawn to match. ESP32-C3-DevKitM-1 A RISC-V board that runs your firmware at 160 MHz on the real memory map. Pushbutton A 12 mm tactile switch. Hold it while the simulation runs. Raspberry Pi Pico The RP2040 board on our own Cortex-M0+ core. Pick a program and press Run. Raspberry Pi Pico W Raspberry Pi Pico W (RP2040). The same board and the same pinout as a Pico, with the CYW43439 on it. The WiFi is simulated (no radio; real internet through the Cloud panel’s switch), and the on-board LED, which hangs off that chip rather than off GP25, is driven through the same path. Everything else is the Pico. Raspberry Pi 4 Model B Raspberry Pi 4 Model B: the 40-pin header, driven by main.py with RPi.GPIO or gpiozero. See every part ## Wire up the DPDT relay Open the editor and push it into the breadboard. It is free, and it runs on your own machine. Start building free Open the editor