# Trip a 5 volt relay using a frs radio

#### James Millett

Joined Apr 4, 2019
10
Forgive me if this has already been discussed. I can’t find anything.

I am looking to make a remote cutoff for my 3 year olds dirt bike. There is no power on the bike ( dc anyways ) what I would like to do is take a pair of frs radios mainly because the range would be far better than I would ever need.. I would like to find a way for the speaker output via a headset plugin can trip a 12 volt relay. The lowest voltage I can find for a relay to work is 5 volts.. anyway to make this work?? You all are way smarter than I! It hurts my head trying to figure it out although I do enjoy the learning of electronics.. any help would be greatly appreciated!!

#### wayneh

Joined Sep 9, 2010
17,167
Can your radio produce a ringer tone? (Mine do). I think you could come up with a way to detect that tone and trip a relay. There may be a better solution but I’m at a loss.

#### James Millett

Joined Apr 4, 2019
10
Can your radio produce a ringer tone? (Mine do). I think you could come up with a way to detect that tone and trip a relay. There may be a better solution but I’m at a loss.
It has a call button that produces a ring type tone. How would I get that to work? That probably could work better in case someone was to talk on the freq I would be using. Either way I’m willing to try!

#### Ya’akov

Joined Jan 27, 2019
5,533
Just a note, this would be completely in opposition to FCC regulations. It would be better to use some high reliability remote control device. There are many options available now, boards with key fobs, etc. They are cheap and ready to be used.

#### Ya’akov

Joined Jan 27, 2019
5,533
Just a note, this would be completely in opposition to FCC regulations. It would be better to use some high reliability remote control device. There are many options available now, boards with key fobs, etc. They are cheap and ready to be used.
I will also add that since this is a safety device, consider that FRS is very prone to interference from other users and may suffer from either false activations or blocking of intentional ones. Devices intended for remote control will be much more robust, and given you are trying to protect someone, I’d look there first.

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#### James Millett

Joined Apr 4, 2019
10
I will also add that since this is a safety device, consider that FRS is very prone to interference from other users and may suffer from either false activations or blocking of intentional ones. Devices intended for remote control will be much more robust, and given you are trying to protect someone, I’d look there first.
Interesting.. didn’t know it would be illegal. And yes the interference in these radios had crossed my mind.

#### Ya’akov

Joined Jan 27, 2019
5,533
Interesting.. didn’t know it would be illegal. And yes the interference in these radios had crossed my mind.
Remote.control is not a permitted use in the FRS service.

I’ll try to find a candidate device when I get the chance to sit down.

#### MrSoftware

Joined Oct 29, 2013
2,027
What level of dirtbike are you talking about, and where will it be ridden? One of those toys-r-us 2mph creepers for the front yard, or something more substantial like an OSET or a JR50, etc..for the local mini track or off-road? If you feel the need for a parent-controlled safety cut-off, a string lanyard would be much safer than wireless. Back in the day, some of the little kid sized Suzuki bikes came with rear mounted lanyards for the parent to hold while following the rider around. If a kid-mounted safety cut off would be OK, then OSET makes one for their bikes, maybe you can adapt it: https://osetbikes.com/gb/parts/pre-2015-parts/switches/official-oset-magnetic-lanyard-kill-switch/ There is a trade off though; loosing power at the wrong moment (accidentally tripping the switch) can be a guaranteed fall. Having grown up on dirt bikes,and teaching my son to ride from a young age, it's a great time to introduce proper gear and get them used to it. Check ebay for used boots, etc.. kids outgrow that stuff long before it's worn out.

#### James Millett

Joined Apr 4, 2019
10
It’s a 2018 Honda CRF50F my 3 year old is riding it. He does well but has those moments when I would like to be able to shut him down. Has all the gear and we have helmet communications.

This bike has no power. I have a bulldog security “remote anything” that I hooked up with a 9 volt battery but I’m guessing the receiver antenna needs more power because it doesn’t work unless the remote is right against the antenna.

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#### shortbus

Joined Sep 30, 2009
9,328
Would a RC car transmitter and receiver work for this? That way a battery from one could be used to power the relay and shut down the bike. One of the cheaper ones with only 2 channels should be plenty to do this.

#### Externet

Joined Nov 29, 2005
1,818

#### James Millett

Joined Apr 4, 2019
10
I’ll check that link.. everything I have found required 12 volt power. This bike has no battery and no dc producing stator or rectifier if I’m saying this right

#### Ya’akov

Joined Jan 27, 2019
5,533
Would a RC car transmitter and receiver work for this? That way a battery from one could be used to power the relay and shut down the bike. One of the cheaper ones with only 2 channels should be plenty to do this.
It is a possibility but possibly a little costly.

#### MrSoftware

Joined Oct 29, 2013
2,027
It’s a 2018 Honda CRF50F my 3 year old is riding it. He does well but has those moments when I would like to be able to shut him down. Has all the gear and we have helmet communications.

This bike has no power. I have a bulldog security “remote anything” that I hooked up with a 9 volt battery but I’m guessing the receiver antenna needs more power because it doesn’t work unless the remote is right against the antenna.
Excellent! He will really enjoy that bike. They haven't changed much over the years and will last forever. I've still got a 1986 Z50R, the much earlier version of that bike which was my first bike as a kid. As I'm sure you're aware, those things will bogey if you don't use the throttle stop, probably 30-ish mph top speed.

The ignition system on those bikes may not be friendly to RF so be sure the receiver is as far as possible from the coil and spark plug wire. Up under the tank is probably physically convenient location to mount stuff, but it's right next to the coil which would be bad for radio performance. If you got the bike used, make sure it still has a resistor type spark plug in it, I think the proper one for that bike is the NGK CR6HSA. A non-resistor plug can make interference from the ignition system worse. The RC car/plane type of remote isn't a bad idea, they will run for hours on a small battery and can have reasonable range. And you can get them relatively cheap on Amazon, but you'll need to come up with a relay of some sort to actually kill the bike. You'll probably want a latching relay, so the ignition stays off until the motor stops spinning if the radio signal is iffy. Also remember that anything high frequency (2.4GHz) won't penetrate well, which means it probably won't work if you get some trees between you and him.

#### Ya’akov

Joined Jan 27, 2019
5,533
The ignition system on those bikes may not be friendly to RF so be sure the receiver is as far as possible from the coil and spark plug wire. Up under the tank is probably physically convenient location to mount stuff, but it's right next to the coil which would be bad for radio performance. If you got the bike used, make sure it still has a resistor type spark plug in it, I think the proper one for that bike is the NGK CR6HSA. A non-resistor plug can make interference from the ignition system worse.
I suspect the reason his current attempt is failing is the RFI from the ignition system. It might be necessary to increase the filtering on it. I don't think small engines like that, are there?

Maybe something like this: https://www.oreillyauto.com/detail/...d8113/acdelco-ignition-condenser/d204/2491796

#### shortbus

Joined Sep 30, 2009
9,328
It is a possibility but possibly a little costly.
I don't know, how much is his kid worth? A quick look before I suggested it show a transmitter and receiver combination for ~ $50. at HobbyTown, and they aren't the cheapest place to buy from. Thread Starter #### James Millett Joined Apr 4, 2019 10 I suspect the reason his current attempt is failing is the RFI from the ignition system. It might be necessary to increase the filtering on it. I don't think small engines like that, are there? Maybe something like this: https://www.oreillyauto.com/detail/...d8113/acdelco-ignition-condenser/d204/2491796 Even with the bike off and the low power the remote I have is lacking on range. Still have to be right on top of antenna to activate it. I was thinking the receiver need the full 12 volts to work well. #### Ya’akov Joined Jan 27, 2019 5,533 I don't know, how much is his kid worth? A quick look before I suggested it show a transmitter and receiver combination for ~$50. at HobbyTown, and they aren't the cheapest place to buy from.
I am not sure there is an advantage of that approach over the standard, much cheaper 433MHz options that are everywhere.

That's what I meant.

I don't know, how much is his kid worth? A quick look before I suggested it show a transmitter and receiver combination for ~ $50. at HobbyTown, and they aren't the cheapest place to buy from. He mAybe worth$45 not sure if I’d go the full \$50 lol