Problems getting H-Bridge to work as expected with electromechanical display

[system]

Hi guys,

Electronics newbie here. I'm trying to get some electromechanical vane displays (bought second hand from Latvia off eBay) to be controlled by an Arduino. I feel so tantalisingly close, but am thwarted. I'd appreciate any help I can get.

So let me fill you in with the details. First the 7-segment electromechanical vane displays:

I've got limited data on these. Essentially each segment is controlled by one coil. Place a current impulse (>50ms) across the coil and it will generate an electromagnetic field and flip the segment out. Reversing the current across to coil generates a magnetic field with opposite polarity and the segment flips in.

From what I can scrounge up, the coil requires a between 20-30V to work. Using an adjustable power-pack, I have found that 24V works fine. (the power-pack is rated 1A at 24V; the resistance across each coil is about 50 Ohms).

To interface the Arduino with the coils, I chose to use SN754410 1A H-Bridge chips (data sheet here: https://www.sparkfun.com/datasheets/IC/SN754410.pdf). Using it in a Full H-Bridge configuration, I should be able to drive two individual segments out and in by reversing the polarity.

I constructed a simple circuit to test an individual segment: (NOTE I missed putting a wire in the diagram between +V from external power source and pin 8 (it's there in real life).

And used the following code for the Arduino

int segmentOUT = 4;
int segmentIN = 5;

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.
  pinMode(segmentOUT, OUTPUT);     
  pinMode(segmentIN, OUTPUT);  
}

// the loop routine runs over and over again forever:
void loop() {
  
  //Sent a 50ms pulse to put segment to OUT position
  digitalWrite(segmentOUT, HIGH);
  delay(200);
  digitalWrite(segmentOUT, LOW);
  //Delay 2s
  delay(2000);

  //Sent a 200ms pulse to put segment to IN position
  digitalWrite(segmentIN, HIGH);
  delay(200);
  digitalWrite(segmentIN, LOW);
  //Delay 2s
  delay(2000);
}

Now, if I replace the coil in my circuit diagram with my multimeter, I can see impulses of current going alternating between +24V and -24V as would be expected given the code.

Unfortunately, if the circuit is connected to the coil, there is no flipping in and out of the segment. I have tried playing around with how long the pin is HIGH, but no luck.

I would appreciate any input. Have I done something wrong with my wiring. Am I missing something completely??

Cheers guys!!

[kf2qd]

24V 50 Ohms - thats about 1/2 Amp. What is the actual voltage across the coil when H-Bridge is energized?

[system]

Interesting .. it's only showing just under +4V / -4V across the coil when the circuit is energized. What do you think is happening to the other 20V?? (don't laugh - I'm a newbie).

[system]

With some help, I managed to figure out the problem was because I didn't have the grounds connected between the Arduino and 24V power supply. Once I connected the two ground rails, the circuit started working.

I've updated my diagram to show (and also fixed up my drawing errors previously - like forgetting the lead to pin8).

Thanks all for your help and input. If you can see any further errors in my design, please let me know.