# Diagram for use of 2 coil latching DPDT relay Panasonic TQ2SA-L2

Joined May 21, 2012
2
Hello,

I'm trying to figure out a basic circuit to wire up a 2 coil latching DPDT relay to switch a line-level stereo audio signal, specifically a Panasonic TQ2SA-L2. Datasheet here: https://www.alliedelec.com/m/d/6ec7cf7d6911bb3ba06b633c7af273e6.pdf. My hope is that I can use a single relay IC to turn each stereo input "on" or "off" (basically whether that input gets routed to the amplifier stage.) I understand that I need a diode to protect against voltage spikes when the relay is switched, but I'm not clear which pins the diode would be between.

I guess my biggest problem is that I'm not clear on the operation of the IC and what each pin is for. It looks like pins 1-5 function as one switch and 6-10 function as a separate switch? Pins 1 and 5 are for control. 3 is the signal source and 2 and 4 are the signal outputs?

Sorry for the remedial-level question, I've been reading threads on other 2 coil latching relays, but I can't tell how they apply to my chip.

Thanks,

Tom

#### Ian0

Joined Aug 7, 2020
9,495
Sometimes don't you just wish they'd use the same terminology as everyone else?
Form C = changeover. They could have drawn a changeover contact like everyone else does, but they just had to do it their own way.
Pins 3 and 8 are common. Pins 2 and 9 are the normally closed contacts, and pins 4 and 7 are the normally open contacts. 7,8 and 9 form one pole; 2, 3 and 4 form the other.
As it's a latching relay, the word "normally" doesn't have much meaning here.
If you energise the coil between pins 1 and 5, the normally open contacts close, and if you energise the coil between pins 6 and 10 the normally closed contacts close. Polarity is important on the coils.
As there would be some transformer action between the coils, I wonder if it would be better to use diode+zener instead of just a diode to suppress the spikes from the coils.
Probably describing it as a "chip" isn't the best!

#### crutschow

Joined Mar 14, 2008
34,038
Below is the relay switch diagram to help clarify:

Applying voltage to pins 10(+) and 6(-) puts the contacts in the position shown.

Appling voltage to pins 1(+) and 5(-) sets the contacts to the opposite position (connection between pins 7 & 8 and pins 3 & 4).

Two 1N4148 diodes (or similar), one connected between pins 10 (cathode) and 6 (anode), and one between pins 1 (cathode) and 5 (anode) will suppress any relay coil inductive transients.
See no reason to add a Zener.

#### Ian0

Joined Aug 7, 2020
9,495
See no reason to add a Zener.
My reasoning is that both coils are wound in antiphase on the same magnetic core. Connecting 12V across one coil will produce 12V across the other coil in the opposite direction, which will be shorted out by its diode. A latching relay needs a nice big magnetic pulse to overcome the permanent magnet holding it in place, I'm thinking that the diode might compromise that. (Thought experiment only, I haven't tried it - the only latching relays or contactors I have used are the single coil version)

#### crutschow

Joined Mar 14, 2008
34,038
Connecting 12V across one coil will produce 12V across the other coil in the opposite direction, which will be shorted out by its diode.
Even if that were true, the effect would only be momentary, and then the current in the activated coil would generate the magnetic field needed to overcome the permanent magnet field and switch the contacts.
The only effect I can think of, would be to double the initial coil current until the transient is over.
The diode would have no effect on the DC field after the initial transient.

#### MisterBill2

Joined Jan 23, 2018
17,790
any inductive spike protection across the relay coils is only needed if you are controlling them with a semiconductor device. If those low power coils are operated by a mechanical switch there is no need for diodes. AND you can also use resistors across the coils and not be concerned about polarity. At 12 volts and momentary pulses.the 1000 ohm resistor will not waste enough power to be a problem

Joined May 21, 2012
2
Thanks everyone! Seems straightforward now that ya'll have confirmed the pinout for me.

If it makes a difference regarding zener or no zener, I'm only using the 5v version, not 12v. I'm not sure yet if my control will be purely mechanical or if there will be some sort of programmable microcontroller so I'll probably go ahead and include the diode if I build some little daughter boards for prototyping with the relays.

@Ian0 are you suggesting not using 'Chip' because it implies something programmable? I was thinking that it was a workable colloqualism for pretty much any sort of IC.

#### Ian0

Joined Aug 7, 2020
9,495
But it's not a chip, or an IC - it's a relay. "Chip" or "IC" implies some sort of semiconductor, more complex than a couple of transistors.