Latching relay not working

Question

I'm pretty new to electronics. I've however recently used mechanical and solid state relays successfully. Now, I am just started trying to use latching relays. I am currently trying to create a set up whereby my raspberry pi would trigger the latching relay to both set and reset positions, thereby switching the main circuit on and off. However, I am encountering some problems as the relay does not seem to latch when the appropriate current is applied to set and reset coils. The schematic of my relay is:

The datasheet can be found here: http://docs-asia.electrocomponents.com/webdocs/1398/0900766b8139805d.pdf

Pins 1 and 6 will be connected to GPIO pins of my raspberry pi, while the main circuit that will be switched on and off will be connected across pin 10 and 3. Since I read that the operate voltage of a latching relay is 3.75V (based on nominal voltage of 5V), I used an adjustable voltage regulator to convert my 9V power supply to around 3.75V. I applied this 3.75V voltage to pins 1 and 6, one at a time, and the GND of pins 12 and 7 to the emitter pin of my transistor which drains to my raspberry pi GND. I also applied 9V across pins 10 and 3, where pin 3 leads to GND of the circuit. When I ran my looping raspberry pi script to cease the voltage across pins 12 and 1, I verified with my multimeter that the voltage dropped to zero from around 3.75V before rising back up again after a few seconds. I expected that current will pass from pin 10 to pin 3. However, the latching relay did not work and I confirmed with my multimeter that no current passed from pin 10 to 3 when set voltage is applied, and I did not hear any expected clicking noise during operation. I then activated the reset coil instead and find that there is still no current passing from pin 10 to 3, or any latching sounds produced. Could any advise me on this issue?

I've also drew a schematic as well. The schematic for the relay is not the exact one I used, since there are limited options on the circuit lab sketch, but this diagram should otherwise be about the same as my current set up with one GPIO pin used.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

Just to be sure we're on the same page, relay coils are between pins 1-12 and 6-7, not between 3-10. Also note that Q2 has some voltage drop even when turned on, so if you set the PSU to the latching voltage, the relay will see a smaller voltage and may not activate. Set the PSU to "rated" voltage, i.e. 5V. You could even leave it at 9V, since the relay is guaranteed to withstand up to 10.9V, though that's getting pretty close to the limit which is OK for a prototype but not advised for long-term usage.