Plan from relay

Hello, have this relay board, how can i connect this board to a printer port (LPT1) and can this port cope with the amps needed to drive the board? I am not an electrician, so please take notice of this fact in your answer. This relay is needed to switch a router motor on and off, the signal is send from "Mach3" (Milling software) through the printer port (LPT1). The motor is 1050w 5a 230v AC.

  • \$\begingroup\$ You have to supply some information about the relay and the transistor (Q1). Otherwise it is impossible to tell if the power from the LPT1 port is sufficient for driving the relay. \$\endgroup\$ – Ariser - reinstate Monica Dec 30 '15 at 17:52
  • \$\begingroup\$ @Burgy, this won't be too difficult. The LPT1 port will output a 5 V signal for on/off, we'll use that to energise the relay and the relay will switch the router. Can you provide a model and link for the relay board? \$\endgroup\$ – Transistor Dec 30 '15 at 18:12
  • \$\begingroup\$ @Transistor, here the link to produckt: ebay.de/itm/… \$\endgroup\$ – Burgy Dec 30 '15 at 19:51
  • \$\begingroup\$ HC-11 433MHz Wireless Serial Port Modul Betriebsspannung: 5V DC Schaltleistung: Gleichspannung: DC - 28V 10A Wechselspannung: AC - 250V 10A Stromverbrauch : 20mA - 85mA (Je nach Zustand, nicht geschaltet, geschaltet) \$\endgroup\$ – Burgy Dec 30 '15 at 19:55
  • \$\begingroup\$ @Burgy: OK. I understand the schematic now. We're going to need to pick up a +5V supply somewhere. I presume that you're using the LTP port for Mach3 already to control the stepper or servo motors. Can you figure out if there's a 5V power supply on that interface that we can use? \$\endgroup\$ – Transistor Dec 30 '15 at 20:08

enter image description here

PC parallel port pinout.


simulate this circuit – Schematic created using CircuitLab


  • Connect the relay board ground to a parallel port ground AND to the stepper board GND or negative.
  • Connect the relay board Vcc to the stepper board +5 V.
  • Check the Mach3 software and assign a parallel port output pin to the router.
  • Connect that pin to IN1 on the relay board.
  • Power up and run the software. If all is well you will hear the relay click when the router is supposed to be on. It looks as though you have an indication LED as well.
  • Switch your multimeter to continuity check and you should get continuity between the outside two terminals of relay K1 when the LED is on. If so, they're the contacts to cut into your router live wire.
  • Wire up the mains as shown in the schematic. Don't skip the fuse or the earth / ground.

Good assembly practice

  • Mount all the boards properly with screws or PCB standoffs. You don't want live PCBs swinging around in your control panel.
  • Keep the mains wiring well separated from the low-voltage wiring by sensible orientation and layout of the boards and routing the wiring separately.

How it works

Mach3 will pull the port output pin low causing current to flow through D1 and D2 lighting them both up. D1 is half of an optocoupler and it turns on transistor Q1 allowing some current to pass through. This turns on Q2 allowing current to pass from the +5, through the relay and through Q2 to the negative. This energises the relay. Relays are notorious for giving a high-voltage kick from the coil when switched off. This puts Q2 in danger. D3 prevents the high-voltage kick and protects the transistor.

Relay board top view Relay board bottom view

Note that the two GND terminals are connected.

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  • \$\begingroup\$ Thank you, time to get some standoffs and the correct connector/plug, ph2.0 4-pin i think so that the PCB gets mounted properly. Best regards, Burgy \$\endgroup\$ – Burgy Jan 1 '16 at 15:52
  • \$\begingroup\$ the pcb has GND twice, are they to be joined? pin1(JD-VCC) connected to pin2 (VCC) with a Jumper, pin3(GND) ,pin4 (GND), pin5(IN1), pin6(IN2), pin7(VCC). \$\endgroup\$ – Burgy Jan 2 '16 at 8:15
  • \$\begingroup\$ @Burgy, the schematic you posted doesn't show it but the two GNDs are probably connected by PCB traces. Check for continuity with your multimeter and have a look at the traces to be sure. If I've found the right images for the board then they are connected. See my updated answer. If this all works out for you then please accept this as the correct answer. \$\endgroup\$ – Transistor Jan 2 '16 at 11:25
  • \$\begingroup\$ @ŧransistor, Thank you, your answer is 100% correct.Best regards, Burgy \$\endgroup\$ – Burgy Jan 3 '16 at 8:39

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