51: Yet More About Relay Switches

I've discussed relays in earlier posts, but I keep learning more. I used 4 relays to swap cold/heat on a Peltier device. Now I need to switch polarity on 2 motors using a single Particle Photon. However, the Photon only has 8 digital GPIOs. My 4-relay plan would use all of them. So I asked around and came up with this arrangement:

This wiring works and takes only 2 GPIOs per motor. I tested with a multimeter. Here's a bit of code:

#define SW1  D1

#define SW2  D2

. . . 

void setup() {

   pinMode(SW1, OUTPUT);

   pinMode(SW2, OUTPUT);

. . .

}

void loop() {

. . .

    // blue wire +

   digitalWrite(SW1, HIGH);

   digitalWrite(SW2, LOW);

. . .

   // green wire +

   digitalWrite(SW2, HIGH);

   digitalWrite(SW1, LOW);

. . .

   // all OFF

   digitalWrite(SW1, LOW);

   digitalWrite(SW2, LOW);

. . .

}