Electronics Newbie needs help with a simple (I think) project

[KalJer]

Hi guys,

I ride a motorcycle and find that I am unable to hear my radar detector at speed. I have found several solutions, one of which is called the Radar Screamer which consists of a 108db Piezo buzzer and various wiring (**broken link removed**) It seems a little ludacris to me to spend $100+ US on something that seems relatively simplistic.

I purchased a 108 decibel speaker at a local electronics store that appears identical to the one sold in the Radar Screamer kit, but could not get it to work. I put a volt meter accross the earphone cord going from my detector to the speaker and found even when the detector was actively going off, it put out less than 1Vdc and 1 Amp.

I was wondering if there was a type of switch/relay that I could use so that instead of powering the speaker (which it obviously isn't powerful enough to do) the switch would avtivate upon sensing voltage/current and let 12v directly from my motorcycle to pass through to the speaker, then when current from the radar detector stops, the switch would flip back.

Does that make sense? Is this possible? I could just buy the radar screamer but at this point I am motivated to get this to work just for the sense of accomplishment if nothing else.

Any help would be much apreciated.

Thanks,
Jeremy

 

[Optikon]

Yeah, you can do this. Speakers need AC. Most Buzzers accept DC (you can find one for 12V)

Maybe something like this:

Radar Detector Output ---> Transistor ---> Relay ---> Buzzer wired to 12V.

Depending on power requirments of buzzer, you may be able to eliminate the relay. And you may need some signal conditioning on the detector output to get it to switch ON/OFF the transistor.

 

[audioguru]

If the speaker you bought can pass the frequency from your earphone output then all it needs is a power amplifier.

 

[KalJer]

Thanks for the replied guys, I have thought of both of those solutions but simply am not knowledgeable enough to execut them.

I can't seem to find any place that sells an amplifier (I assume inline) for the purpose...radioshack doesn't seem to have anything, anyone in the states or canada have any ideas? I'd love to be able to finish this today if possible and am located just outside Chicago.

As for the relay, I have no clue on what specs I would need or where to get one of these as well...

Any input would be much appreciated!

Thanks,
Jeremy

 

[philba]

there are tons of web stores with audio amp kits. some quite cheap. I doubt you need much fidelity. there are also lots of chips with designs you can lift directly from the datasheets.

you can also find sound activated relay kits which is basically what the screamer appears to be. for example: **broken link removed**
that one would take a little adaptation as it uses mic input. I have no idea of the quality of the design, especially for the automotive envt.. also, adapting to an auto envt would probably mean adding a diode to prevent reverse polarity.

 

[evandude]

First you need to find out whether your piezo buzzer has a built in driver or not. If it has a driver, all you need to do to get it to buzz is to apply a DC voltage, and so a sound-activated switch circuit (something like philba posted) would probably work best. If it does not have a built in driver, then you would have to drive it with an audio amplifier as audioguru said. If you were to go with the sound-activated switch that philba posted, quite possibly the simplest way to adapt it to use the line-out output of your radar detector when it's designed for microphone-level input, would be to simply plug a small earphone into the radar detector and tape it to the microphone

I would guess that since it's a super loud buzzer which is typically used for an alarm type system, it probably has a driver in it... But you'd have to check the package, or ask the people you bought it from.

 

[mramos1]

Maybe use the 1 volt to drive a transistor, to drive a solid state relay for the buzzer. Power it off the bike battery. I saw 1 AMP SSR at allelectronic.com for $1.75 (but there is shipping too). What kind of draw does the siren require?

Electronicsgoldmine had 10 AMP for $5 range. I bought 5 myself.

Could you not drive an FET to power it with a current limiting resistor on the siren?

 

[KalJer]

No info on the package really (just radio shack, voltage, amperage, etc)

I wired it up to a cigarette lighter plug and it worked...maybe next time I'll point it away from me first...

So what is the best method do you think? Will the sound activated relay work even though it seems to put out less than 1V even when it's sending a signal (going off / alerting) won't I still need an amplifier since I need more than 1v to drive the speaker?

 

[audioguru]

It works when powered from the lighter jack so it is not a speaker, it is a buzzer or a siren. It doesn't need an amplifier, it needs 12V power when the alarm goes off. A signal-activated relay would apply power to it fine.

 

[KalJer]

Alright so the signal activated relay (like **broken link removed**one?) Gets wired to the 12v battery on the bike, a ground, the buzzer, and the signal source (in this case the radar detector), when it senses signal/sound from the radar detector it closes the switch allowing 12v to flow from the motorcycle battery directly to the buzzer.

Is that correct?

Thanks for your help everyone!

Jeremy

 

[audioguru]

Attach its microphone to the earphone of the alarm and it should work.

 

[KalJer]

but the relay also gets wired directly to the 12v (+) right?

 

[mramos1]

Attach its microphone to the earphone of the alarm and it should work.

I thought he only had 1 volt out on the earphone (EDIT: I typed mic, but meant earphone).

Kaljer:

On side of relay contact to +12, other contact to red wire on siren, black wire on siren to negative. But you will need something to drive the coil, I thought you said you only had 1 volts? Can you drive it from the internal siren or you do not want to open it?

 

[audioguru]

I thought he only had 1 volt out on the mic.

The input to the Voice Activated relay Circuit is the microphone that it comes with.

 

[KalJer]

Does anyone know of a sound activated relay circuit that has no time delay (as opposed to the other one that has a delay of 1-60 seconds...even 1 second can be a big deal in this application)

Also for the above kit, do I just cut off the microphone and wire the headphone cord directly to the pcb via the microphone wires?

Thanks,
Jeremy

 

[963Exp]

I'm not familar with your particular radar detector. However, I had a similar application several years ago. Most radar detectors have some sort of a light that illuminates at the same time as the sound emmits. If that is the case then you can take advantage of that power source.
What you have is a piezo electric buzzer, although it is really classified as a speaker, the arrangement you currently have is equipped with a driver rated at 12 volts. So, when you apply 12 volt power (in the proper polarity) it will emit a very loud tone.
Now go back to your radar detector and open it up. Find the two leads that go to the light. Using a volt-ohms meter, measure the voltage on the back of the light and note the polarity. If you have anywhere between 9 and 13 volts, then this is the place where you can tap into to make your external buzzer scream when the light is illuminated.
Of course, if this is a newer technology radar detector, then it is probably equipped with LED's rather than a 12 volt bulb. If that is the case, then you'll only see about 3 volts max on the back of the LED. At that point, you are going to have to add a transistor in order for the 3 volts to switch the 12 volt buzzer. Yes, you could do this with a relay, but you are making this a much more complicated project at that point.
The project that I did this with was over 20 years ago and I had remotely mounted radar detectors on both the front and rear of my vehicle. I went directly to the 12 volt bulb to drive a piezo buzzer. It worked great. Radar detectors have came a long way since then, but the basic idea remains the same.
Hope this helps.
-K

 

[KalJer]

The radar detector is a Valentine 1, so the issue is that it can be any one of 3 lights illuminating (the V1 uses an arrow system to indicate where the radar source is relative to you)

Opening the detector is not something I am about to do, at $400 each + shipping that could prove to be a very costly mistake.

V1's utilize a 4-conductor telephone wire, and I think one of them is for lights, I will try to get an extra cord and put a meter on that wire. Can I impliment a transistor in any fashion without opening the detector casing?

Thanks,
Jeremy