Electronics Gurus - Help Needed!

[ragingfish]

Hey all...I know I've been kind of quiet on the posting front lately...my job is made insane, and it's taking a lot of time (and sanity) from me. I do pop in to read daily, but rarely post lately. Anyway, I need everyone's help with a little project. Everyone knows (or should know) the story of Ragingfish's new G6 and the deer that hit it the day after delivery. Shortly after that, I bought something I found online, an "electronic deer alert."I never installed it until last week because, by the time my car came home from the body shop, it was too cold to put in. But with the recent heat wave we had, I opted to put it in last week. Here's the thing. The deer alert has two "modes." First is ultrasonic mode. It emits ultrasonic tones to scare off small animals like dogs, cats, raccoons, etc. This mode is ALWAYS active. Then there's an audible mode, that emits "chirps" at random intervals, to scare off larger animals, such as deer. This mode isn't activated by default. To activate it, you have to start the car, then stop it, then restart it. The device senses the changes in voltage between the engine being on/off and interprets that to turn the mode on. The device is also hooked to +12, not ignition. Now, I'm having a problem where, even with the car off, there is trickle voltage in the system, so the device never shuts off. So I want to move it to an ignition controlled circuit. Problem is, without it always having +12, it will never activate audible mode because even if I turn the engine on/off, it willl turn the power source on/off, and not just put out reduced voltage.Here's my idea. I ran wiring to the dash, and wanted to install a hidden momentary button that, instead of being on/off, would be SPDT, so that, the "constant" position would be connected to an ignition controlled circuit, allowing the device to work only when it has +12, and the other "throw" would be hooked to a circuit that I could design that would "trick" the device into thinking the engine is being turned off, then on again, by , I'm guessing, some sort of resisitor setup, that would drop the voltage down to an equivocal level of the engine being turned off. Who can help me design this circuit? I'm trying to keep it very simply, am not an expert electronics guru, and my soldering skills are fair, at best. But for obvious reasons, it's important to me to be able to have the device running, and my preference would be to not have to constantly start and stop the engine to get audible mode running (can't be good for the engine either).Jahntassa found me this link to a voltage divider circuit: http://www.play-hookey.com/dc_....htmlBut wasn't sure which resistors or resistor combos would be required to drop the voltage to a level that mimics that of an engine that is off.Who can help ragingfish out???Oh, and if I can get some responses today or tomorrow, that'd be stellar, I'm off work until Monday night and really want to get this project done before then.Thanks everyone!PS -- In case my description of the device confused you, I'm attaching to this post the scanned instruction sheet. Hopefully it can clear up any confusion over what I attempted to describe.

Attached files deeralert.pdf (29 KB) 

[joatmon]

how much current does it draw, - or - what is the rating of the fuse?If it was me, instead of worrying about balancing the voltage divider, I'd hook up a couple (or maybe three, depending on what it takes to make it work) diodes in parallel with a normally closed switch. When you open the switch, the current has to flow through the diodes and each diode will drop ~0.7V, regardless of current draw. Something like the attached pic maybeΩ

Attached files

[ragingfish]

joatmon: do you think that a 1.4V drop will be enough to make it think the engine shut off?

[spoonman]

Mike,You could trying measuring the voltage on hookup wires for the deer alert and watch what voltages it "sees" as you go through the steps to activate the other mode. Then as joatmon hinted, once you know how much current it draws, you could figure out what the resistor value/s would need to be as well as what current rating the resistor would have to be. Might be a good place to start at least.Vern

[AKLGT]

yes, you definitely need that! sorry, i can't add to comments already made. I'm still trying to figure out the power issue on my car PC.

[spoonman]

joatmon: good idea with the diodes.ragingfish: 2 diodes might do it, but I am guessing it will need 3. You figure that your battery should measure ~12V when the engine is not running, and ~13.8V or so when it is running. So with a difference of 1.8V, you might need the 3rd diode to get enough of a drop. It mostly depends on how sensitive the circuit is in the deer alert that monitors the voltage change.

[ragingfish]

Thanks for the tips guys. I took a voltmeter to it, and measured 12.3 for the engine off voltage. Engine running voltage has typically run anywhere between 13.5 and 14.3...my radar detector can play voltmeter too, and I usually leave it in that mode for kicks.So would resistors or diodes be better? And I'm sure even if I use resistors, I have to throw a diode in to ensure I only run reduced voltage when I press the button.And either way I go, which diodes and/or resistors should I buy? Thanks y'all!Oh, and joatmon, it uses a 1A fuse.

[joatmon]

You could use resistors or diodes, bt there's no reason to use both. Like I said, I'd use diodes. less math THe cheapest diodes radioshack sell can handle an amp, and they'll drop .7 V regardless of curent. pack of 2 for $.59UShttp://www.radioshack.com/prod...earch two might work, but if you buy two packs of 2 and don't need a third, then it's not like you go hungry for wasting the money.

[ragingfish]

Joat:If I didn't use a diode and only used resistors, wouldn't I run the risk of the current flowing backwards through the resistors, and dropping the voltage level when I didn't want it to?

[Jahntassa]

Not if you run it through a relay Just put the resistors on one leg (87), the non-resistor side on the other (87a), and the output to the thing on 30.

[ragingfish]

I tried hooking up 6 diodes in parallel, and only achieved a reduction of 0.3V. Then I tried hooking up six diodes in series instead, and achieved a voltage reduction of approximately 1.6V. I still have another 1V or so to knock off. What's the deal? Thoughts?

[joatmon]

doesn't make sense to me, series would be the eway to go, not sure why you are getting such a small drop

[ragingfish]

there are different kinds of diodes, could i be using the wrong ones? i'm using rectifier diodes...2.5A, 1000V

[ragingfish]

Folks, I think I found my answer!Poking around at the rat shack tonight, I stumbled across this:It's a +12V voltage regulator. I can give it up to +35V input, and it will ALWAYS output +12. Even simpler then the diodes!!!Will have to test it out tomorrow.

[mikey00]

Have you checked with the manufacturer for a simpler solution? Most electronic deer alerts come with a switch or provide another means of on/off. It looks like you have the one from AutoSport, which uses current sensing but does claim it is only on when the engine is running. If yours is on when the engine ifs off there may be some other problem/solution other than designing a circuit.

[ragingfish]

I've been workign on this project on and off for a month or so, and I think I found a solution. I built the following circuit, and with an 18V power supply tested it to successfully drop it down to +12. So now the question becomes, will it be enough to trick the deer alert. I'm going to install it today, and I guess we'll find out! I'm sure SOMEONE will ask, but the reason I used a screw terminal strip instead of soldering is because my soldering skills mostly suck, and I spent hours trying to solder parts, ruining most, and finally giving up. This will be inside an enclosure, so I don't anticipate any problems with the build.Pics:Circuit Diagram:Built:Switches:I have that extra hole because that is where I originally mounted the switch, but quickly discovered it was too close to the hinge of the compartment, thus preventing it from closing. Oops. New location works beautifully.Stay tuned for final test results!

[Jahntassa]

Don't forget to tape that stuff up!

[ragingfish]

Ladies and germs, I'm ecstatic to report that the circuit performed BEAUTIFULLY!!!Here is a shot of the enclosure mounted behind the dash:The cover installed:Backside of the lower dash with switches installed:I tested it out tonight, and it works great. Once I shift to park and engage the brake, the DRL's cut out, and so does the deer alarm (would be annoying for it to keep going off because of RAP while fueling at a gas station or something). I push the button into "regulated" voltage mode, the alarm thinks the engine shut off and does it's "shut down" noise. Push it again, and it starts up again in audible mode. Works flawlessly!!!Thanks to everyone who helped me out with this project!!!

[zionzr2]

Glad you got it working how did you test ultra-sonic mode???I have alaways been a tad skepticable about the ultrasonic devices actually working...

[ragingfish]

Quote, originally posted by zionzr2 »Glad you got it working how did you test ultra-sonic mode???I have alaways been a tad skepticable about the ultrasonic devices actually working...The thing makes clicking noises that, according to the device's instructions, are signs that it is generating ultrasonic tones.

[kostby]

Just to be on the safe side, better put a warning sign & flashing light on the front for the hearing-impaired NJ deer!