How to drive a relay that is 100 feet away

I have an Argon that is controlling a solid-state relay. The relay is 100 feet away from the Argon.

What is the safest way to control that relay given the distance?

Thanks in advance for your help.

Do you want to have a wired or wireless control? Wired would be the simplest but putting a TTL signal down 100 ft wire is likely not going to work (you have not described the environment) so then you would need to use RS485 and have a control transceiver board at the relay. Running the power cable to the relay that is near to the Argon might be better or move the relay and Argon to the device you want to control?

Thank you @armor.

I prefer a wired setup. Indeed, sending the TTL signal from the sensor via 485 to the relay in the vicinity of the Argon would work but would need more space and in my scenario complicates the wiring and the physical setup.

Would using something like the two approaches below work?

  1. Using a transistor:

  2. Boosting the relay signal to 12V using:

What do you think of those approaches?

I don't quite understand what do you mean ?

sending the TTL signal from the sensor via 485 to the relay in the vicinity of the Argon would work

Your relay should be controlled by Argon or by some kind of sensor ? RS-485 It's a differential signalling system that is frequently used for serial networking interfaces i'm not sure if you can send TTL (Transistor/Transistor Logic) via any serial networking interfaces. I'll suggest you to check SparkFun Qwiic Differential I²C Breakout Board (BOB-14589) along with SparkFun Qwiic Single Relay. They are inexpensive, pretty simple, addressable and can go up to 100 feet.
Also you don't need to worry about power suppy all signals are sent over an Ethernet cable that is attached to the breakout board through RJ-45

Thank you @dreamER. I will look into the device you sent. But can a TTL signal travel along an i2c extender?

I have in the past successfully converted a TTL signal using an RS485 board then converted it back at the microcontroller location. It works fine but is a bit of a hassle to implement.

@Jimmie, It would be helpful to draw a picture of what you are trying to do.

  1. Looks like you want to use a cable.
  2. Should the cable carry power, or is there power at the 100ft spot?
  3. Depending on #2, what about wireless options? LoRa comes to mind.
  4. What does the SSR do?
    If you only want to close a contact at the far side, then the “transistor idea” is simpler. It may be slow
    because it has to charge the line, but you can use a higher voltage.
    You can do that with another SSR at the Argon side; no transistor needed.

Like I said, I do not know (never got to this point) if you can send TTL to RS485 but also I didn’t say that this is not possible :slight_smile: I found pretty smart solution which may be interested for you. Receiving-RS485-signal-and-TTL-signal-with-the-same-RS485-receiver

I think this is a case of sematics :wink:
When you consider TTL as the source signal (even if it’s not exactly TTL levels) and then “translate” them onto a different “carrier” (e.g. current driven vs. voltage driven) then one might refer to this as sending a “TTL siginal” (aka the original source’s “language”) by means of an “intermediate medium”.


Lora would work but I prefer a wired approach. Power is supplied from 100 feet away (SSR location).

The SSR provides a dry contact to another board.

Here is a diagram.


Thank you.

This is just one of a million and one solutions. More details are needed to complete the design.
The 10k resistor is a precaution to discharge the FET and protect its gate.
The other resistors represent the cable resistance and will affect the delay to the SSR turn on.
You will need to pick the appropriate NFET based on what voltage and current the SSR requires.
It also has to have a low Vgs threshold so the Argon 3.3V output can turn it on.
You can also use an SSR in place of the FET.

You might want to look into the cost as well. 100ft of cable is not cheap and could totally change the implementation.

Thank you @Pescatore for taking the time to draw the circuit and for your help.

The SSR delay is OK in my application. What is the “Adj” component (connected to 5V)?

I was wondering how would the circuit look like for an SSR at the Boron’s location to control another SSR which is farther down?

Thanks again.

It is a voltage regulator to power the Boron. You have to pick an appropriate one, depending on what power you have available.

[quote=“Jimmie, post:11, topic:54418”]

Got it, thanks.

I added this question after I sent my initial response:

I was wondering how would the circuit look like for an SSR at the Boron’s location to control another SSR which is farther down?

Here you go…
EDIT: You can use various DC-DC converters from Amazon in place of the linear regulator.

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Thank you very much.

A word of caution, also for future readers…
That is a concept drawing, not a complete design.
You will need appropriate SSRs and voltage spikes clamps. The inductance of the cable needs to be managed with snubbers and proper twisting of the wires.
Since this is getting into a topic not related to the Particle devices, DM me with other questions.

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Just my 2 cents.
What is the switching time or frequency? Is it something slow that you’re going to turn on for minutes or hours? Next, how much current does your relay require? if you’re using a solid-state relay and you’re not toggling on and off faster that one or two seconds, simple twisted pair wiring will likely work. At less than 1 Hz, it really just becomes DC, and the primary issue is resistance in the wire causing a voltage drop.
I’m using heavy gauge stranded outdoor CAT 6 cable driving SSRs at 50 feet with no issue. Good CAT 5/6 cable is rated at < 0.188 ohms/meter. 100 feet = 30 meters * 0.188 = about 5 ohms. At 20ma for an SSR and cable distance x 2 for both conductors, that’s a voltage drop of 10 x 0.020 or < 0.2 volts, which is negligible.
Regardless of length, you’d be wise to use a driver, a transistor, 74HCT125 (my vote), or a ULN2003, this help isolate your device.
Regardless of the method you choose, and there’s some good advise above, you do need consider lightning if you live in an area that’s subject to it. I live in Tucson, AZ, and we get some pretty good lighting in the summer. I’ve lost a few device due to nearby lightning strikes radiating into the long cable. Bury it, or put it in grounded metal conduit.

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Thank you very much @tbitson. This is good info.

In my application, the switching time is not an issue.

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