Does anyone have a suggestion for a 12V in, 5V out single-pole, double-throw quiet relay? The standard 5-pin radio shack ones are very noisy. SSRs don't provide the flexibility of giving you both ground and 5V without additional external circuitry...
Thanks!!
Smaller relays tend to be quieter, so if you don't need lots of current that may help. Where I work we use some reed relays which aren't loud, but I can still hear 'em click.
SSRs don't provide the flexibility of giving you both ground and 5V without additional external circuitry...
I'm not sure what that means, but an SSR that's designed for low voltage DC will work in most 5V applications. Or, if you don't need much current maybe you can use an optical isolator, Or, do you really need isolation?
...If you tell us about your application and your circuit, maybe we can suggest something.
It sounds like you want a double pole relay, so you can disconnect the ground as well as the 5v lines. Is that what you want?
We would like to hear a description of your application. We would understand more, and be able to give more pertinent suggestions.
Guys,
Thanks for the quick responses. The application is a series of 12 V automotive signals feeding into an Arduino -- so current requirements are indeed super low. The car sends a series of 12 V signals (either switched, as in the case of doors opening, lights being activated, reverse indicator, etc.) or square functions (from hazard lights, turn signals).
I would like the signal from the relay to give me +5V or ground to feed directly into an arduino. I could obviously just get current through a single-pole single-throw SSR, but then I would have to build in a pull-down resistor circuit for each relay. Space is already tight, so I would lik eto avoid this if I can.
Thanks again1!
" but then I would have to build in a pull-down resistor circuit for each relay"
A double throw relay will not require any pull-down. Most relays are double throw.
You could reverse the logic, and use the internal pull-up of each arduino input pin.
Since you do not need to control current, you may find other (smaller) components rather than a relay, such an a optocoupler.
Consider using reed relays like these. They are small. Although the coil is specified as 12 volts, the datasheet confirms the maximum voltage is 20 volts so there will be no problem when the battery is a little higher than 12 volts during charging.
I am playing around with a similar reed switch today and can just hear a slight click (only on release I think) if I hold my ear close to it in a very quiet room.
Another option is to use photocouplers such as these. You will need a resistor as well but they are very small and you can get tiny resistors!
It is possible to connect the 12V signals to Arduino inputs via voltage dividers but I think you are well advised to use a relay or photocoupler to provide electrical isolation.
Bear in mind that you can get short spikes well above 12V on automotive electrics. A reed relay coil is probably more tolerant than an LED in a photocoupler. Remember to ensure that such spikes do not get through to your Arduino's power supply.
Have you looked at SSR I/O modules?
found at:
You can install one on your +5 VDC wire and another on your 0 VDC wire.
Small, silent, no moving parts, even a 3 amp fuse.
From your description, you should be using opto-isolators.
aarg:
From your description, you should be using opto-isolators.
What's wrong with using a relay?
Archibald:
What's wrong with using a relay?
It's your call. They are much noisier. 
Using relays for multiplexing (selecting / routing various "signals" to one input)?
Relays are slow (very slow).
Mechanical things wear out quickly.
http://www.jameco.com/Jameco/Products/ProdDS/894391.pdf
They are also generally much bulkier than an 8 pin IC.
aarg:
From your description, you should be using opto-isolators.
+1
~1mA should be enough for the opto LED. A 10k current limiting resistor.
That protects the average 30mA opto to 300volt.
Connect the opto transistor between pin and ground, and use the internal pullup resistor.
If you are going to power the Arduino from the car battery, there is no need for all of this.
Just a simple resistor divider is enough to bring the car voltage down to 5volt.
If the resistor values are high enough, e.g. 47k to ground and 100k to user, then it also gives you enough overvoltage protection.
Leo..
[quote author=Runaway Pancake link=msg=2382950 date=1441324842]
Using relays for multiplexing (selecting / routing various "signals" to one input)?
Relays are slow (very slow).
Mechanical things wear out quickly.
http://www.jameco.com/Jameco/Products/ProdDS/894391.pdf
[/quote]The reed relay I gave as an example has a life expectancy of 100,000,000 operations (technical specification). It is certainly fast enough to cope with monitoring doors opening, lights being activated, reverse indicator, hazard lights and turn signals. You can only hear then operating if you hold your ear about 10cm away in a very quiet environment.
I'm not saying reed relays are necessarily the best option for this application but they are certainly a good option.
Archibald:
I'm not saying reed relays are necessarily the best option for this application but they are certainly a good option.
Are they not quite expensive? By the way, do you have a silent car? I'm trying to imagine how you could hear a small relay in a car.
aarg:
Are they not quite expensive?
$2.02 for the example I linked to with 12 volt coil. $1.53 for the 5 volt DIL type that I'm using here.
The photocoupler (opto-isolator) I linked to is $0.15 (excluding the necessary resistor).
Here's a dual optocoupler for 1/3 the price. So 1/6 the price per channel.
Thank you all for the responses... Maybe I'm missing something, but it seems like the vast majority of optoisolators that you guys have pointed to have a max input value of 5 or 6 V, and I'm not sure how sensitive they would be to spiking. Obviously these would be powered by the same line that would trigger whatever system in the car, and it would be 12 V and noisy.
I thought the benefit of a relay is that - given the actuation is based on a simple electromagnet - their susceptibility to voltage spikes or noise is much reduced. Am i right?
I also don't need a high frequency at all. These events are 1/s to 5/s, so fast actuation is not necessarily a need. Multiple cycles is a requirement though, so something tht burns out after 1000 cycles is not going to fly!
aarg:
By the way, do you have a silent car?
The car is actually not that silent... it's just that the Radio Shack relays are THAT bad! They sound like maracas!!!
azarur:
Thank you all for the responses... Maybe I'm missing something, but it seems like the vast majority of optoisolators that you guys have pointed to have a max input value of 5 or 6 V, and I'm not sure how sensitive they would be to spiking. Obviously these would be powered by the same line that would trigger whatever system in the car, and it would be 12 V and noisy.
I thought the benefit of a relay is that - given the actuation is based on a simple electromagnet - their susceptibility to voltage spikes or noise is much reduced. Am i right?I also don't need a high frequency at all. These events are 1/s to 5/s, so fast actuation is not necessarily a need. Multiple cycles is a requirement though, so something tht burns out after 1000 cycles is not going to fly!
No, the input side of an opto is an LED. The only voltage rating it has is Vf, the forward voltage of the diode. But that isn't the input voltage, as you are expected to limit the current with a resistor, just as you would with an LED. You can choose a resistor value to match just about any input voltage.