I'm trying to use a TQ2-L-5V relay. This is the 1-coil version. It's looking for Vcc of 5V across 10 and 1. But beyond that, I'm having a hard time understanding the datasheeet. I'd like to control it using a MCU that has high voltage of 3v3. But I don't understand what pins to apply high/low to. I think 75% of Vcc is important somehow. It's a 5V relay, 75% of which is 3.75v. Maybe I can't get there with the MCU high.
Thanks.

 

A one coil latching relay usually requires reversing the polarity of the latching pulse to activate / deactivate.
The coil can be wired across any two gpio pins for control but iffy with a Vcc of 3.3 volts.
Why not get the 3 volt version, most micro gpio pins can handle up to 40ma and it only requires a brief pulse.

 

It obviously comes in a 3V coil version. As for the other ordering information, I have no idea, can be of no help.

 

Transistor circuit to activate and deactivate with 3.3 volt GPIO.

 

Transistor circuit to activate and deactivate with 3.3 volt GPIO.
View attachment 338455

Transistors are swapped. NPN should be top. R1 not needed.
47u should be two caps so its non-polar.

 

If you used a two-coil latching relay you would not need to have external circuitry to build and install some place. I am not able to simplify beyond that level.

 

Transistors are swapped. NPN should be top. R1 not needed.
47u should be two caps so its non-polar.

Nope.
When the GPIO is low Q1 is ON charging C1 through the relay coil.
When the GPIO is high Q2 is ON and discharges C1 back through the relay coil.
R1 is required for reverse bias because the output from the GPIO is 3.3 volts but the emitter of Q1 is at 5 volts.
Operation verified on bench test.

 

If you used a two-coil latching relay you would not need to have external circuitry to build and install some place. I am not able to simplify beyond that level.

This originally applied to a situation where there was only one GPIO available and required 5 volts.
A 3.3 volt output is too low.

 

Suggestion cancelled. It required two outputs.

 

Use a 74HC inverter. This circuit is self-timed, so that the coil doesn't remain powered if the processor stops.

 

That might work if the output voltage of the inverters remains above 3.75 volts.

 

That might work if the output voltage of the inverters remains above 3.75 volts.

Why 3.75V?

 

That's the minimum voltage required to operate the relay.

 

That's the minimum voltage required to operate the relay.

A HC gate output impedance generally seems to be about 45Ω with a 5V supply, so there is 30Ω in series from 5V. That suggests it might be about 4.45V.
If a HC04 won't do the job, then perhaps four sections of a HC541. It works with both inverters and buffers.

 

It might even be able to work with a CD4049. What I see is that it would require both sink and sourcing enough current. Realizing that, the CD4049 will not work, it can't source much current running at even 5 volts. So the application will require a TTL IC that can both sink and source.

 

Now you know why I preferred using transistors.

 

INDEED! But a single IC is more sanitary and simpler to assemble correctly.

 

View attachment 338537Use a 74HC inverter. This circuit is self-timed, so that the coil doesn't remain powered if the processor stops.

You do realize that L1 is the coil of a single coil latching relay.....

 

In the interest of keeping it sanitary and simpler to assemble here's another circuit.
Both sides of a MC6002 op amp wired in parallel as a comparator.
Output voltage measured 4.4 volts at 20ma.

 

OK, the MCP6002 is an op-amp. Now I wonder if there is an 8-pin comparator that is not open collector that could be used. The motivation being a lower idle current. But not sure if low power was a requirement in this thread.