Simple remote LED project - help

[Concat]

Hi everyone,

New here and I just need some help with a simple project. I took electronics in JR High, but we usually just blew up capacitors if I'm honest...

I'm going to be running 4 chip LEDs off of a 3V cell battery and I would like to be able to include a remote RF switch.

My first question would be... where can I buy a 3v remote switch? My second question is... how do I wire it and what does NO, COM and NC mean?

I was looking at getting this: http://www.ebay.ca/itm/DC3V-5V-Rela...eceiver-Transmitter-M4-T4-L4-/331302632529?pt

Shipping estimate is a month away, so that's no good... but am I on the right track? Any NA distributors you can point me to?

Thanks

 

[Arouse1973]

NO is normally open contact of the relay, I bet you can guess what NC is? Common is the point that you would place your input to be switched. So if you put say 12 Volts on the common with the relay off, you would see 12 Volts on the NC (normally closed contact). When the relay is energised you will see 12 volts on the other terminal NO (normally open) but you won't see it on the NC anymore.
Adam

 

[KrisBlueNZ]

Hi there and welcome to Electronics Point

Yes, I think you're on the right track.

What kind of battery are you planning on using? And what are the specifications of the LEDs?

That particular receiver has a relay output, and while that relay is activated, it will draw extra current to operate the relay coil - the eBay ad says about 30 mA but this may be more for the 3V relay version. That could represent quite a lot of wasted current.

It should be possible to remove the relay from the receiver and use a MOSFET in its place but that will require some SMT soldering (soldering of tiny devices that mount directly on the surface of the board). So if you can find a receive that has a MOSFET output already, that would be better.

 

[Concat]

I'm using a cr2032 battery, and some chip LEDs. The site I bought from said the battery is suitable to run up to 10 of the chip leds. I think the leds are 20 mA?

30 mA sounds like a lot for my set up, but perhaps still doable. How much can a little cr2032 handle? And this 30 mA is when the switch is "on", correct? It says the quiescent current is 3.5 mA... that's how much the switch uses when it is "off"?

Is the relay mechanically operated in this unit, whereas MOSEFET is solid state?

Basically I need to run the 4 leds, plus the switch... sounds like a total draw of 110 mA. cr2032 is typically rated for around 200 mAH. Sounds like I'd get 1-2 hours before switching the battery out, correct?

To provide further inside, this is for a Halloween mask Needs to be a small set up.

 

[KrisBlueNZ]

I'm using a cr2032 battery, and some chip LEDs. The site I bought from said the battery is suitable to run up to 10 of the chip leds. I think the leds are 20 mA?

You can run them at various currents depending on how bright you want them.

A single CR2032 is only 3V. What's the forward voltage of the LEDs? If it's more than about 2V (and it probably is), you won't be able to regulate the LED current. You would be best to use a separate CR2032 for the receiver, and you could just use the other CR2032 to supply all of the LEDs in parallel, and rely on the cell itself to limit the current. This is not the proper way to do it!

Do you have a part number or a link to the data sheet for the LEDs?

30 mA sounds like a lot for my set up, but perhaps still doable. How much can a little cr2032 handle? And this 30 mA is when the switch is "on", correct? It says the quiescent current is 3.5 mA... that's how much the switch uses when it is "off"?

Yes, that' right. How much current you can draw from a CR2032 depends who you ask. 30 mA is manageable, though of course the lifetime won't be very good, and the voltage will be less than 3V because of the cell's internal resistance, which is estimated at 30~50Ω or somewhat higher for cheap cells. I've not seen anyone suggest drawing more than 100 mA from a CR2032.

Is the relay mechanically operated in this unit, whereas MOSEFET is solid state?

Yes.

Basically I need to run the 4 leds, plus the switch... sounds like a total draw of 110 mA. cr2032 is typically rated for around 200 mAH. Sounds like I'd get 1-2 hours before switching the battery out, correct?

I wouldn't expect more than an hour. The 200~225 mAh specification applies at low current; the higher the current, the lower the mAh you will achieve.

To provide further inside, this is for a Halloween mask Needs to be a small set up.

Gotcha. Could you put the batteries in your pocket and run some thin wires up to the mask?

 

[Concat]

A single CR2032 is only 3V. What's the forward voltage of the LEDs? If it's more than about 2V (and it probably is), you won't be able to regulate the LED current. You would be best to use a separate CR2032 for the receiver, and you could just use the other CR2032 to supply all of the LEDs in parallel, and rely on the cell itself to limit the current. This is not the proper way to do it!

Do you have a part number or a link to the data sheet for the LEDs?

Sorry, I really don't know more about the LEDs other than the website I bought them from : http://www.modeltrainsoftware.com/smd-chip-leds.html
It says something in there about not needing to add resistors...

I could use two batteries... but I don't understand how to wire it to the receiver. There are 5 contacts on the receiver in the ebay photo:

One battery to the - and + powers the receiver, yes? But the one for the leds in parallel... how would I connect that? Would I connect the negative terminal to the - contact, then on the positive side connect the leds and then finally to the NO contact? So the negative contact is connected to both batteries? Hopefully you can follow what I mean.

Thanks for your help. Kudos!

 

[KrisBlueNZ]

Right, you connect the receiver's CR2032 to the "+" and "-" connections.

The other three contacts are for the relay output. Normally, the relay on the board connects COM (common) to NC (normally closed), but when the output is activated, it connects COM to NO.

So you need to make a circuit from your LEDs (all in parallel) to the other CR2032, and break the circuit somewhere and connect the COM and NO connections to the break in the circuit.

This will waste power because of the relay. You would be better to use a receiver that has a MOSFET output.

Could you put the batteries in your pocket and run some thin wires up to the mask?

 

[Concat]

Ok thanks for clarifying. I tried a quick search for a MOSFET switch/receiver/remote and I couldn't find anything that I could easily utilize. I probably just don't know where to look or know the right search terms (?)

I could run wires up to the mask, but if I can't get a RF remote to work, I'd probably just settle for a regular push button switch in the mask itself.