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Electronics Forum / Basics / June 2006Need simple timer module or kit for car alarm project
Hi, my car was just broken into yesterday, so I decided it's time to get a car alarm. It's an old car, so I bought a cheap (but good brand) basic vibration sensing alarm. Being the tinkerer I am (and not wanting to irritate my neighbors with false alarms), I want to install a timer that will wait a little bit before sounding the siren. I also bought another cheap alarm system ($20 on eBay) that instead of a siren sends a message to a pager. Thus, assuming both alarms trigger, the neighbor annoying siren won't go off immediately, but I will still be informed. Ideally, these two systems should be combined, so that I'm using the good brand vibration sensor to activate both the siren and pager, but I'll leave that project for later. (Incidentally, I'm also going to install a homemade fuel pump kill switch, but this won't be connected to the alarm system.) I'm thinking I'd need to put an initially open relay in series with the siren and the timer in parallel. When the circuit closes (i.e. alarm tries to go off) the timer gets activated and closes the relay after a certain (hopefully adjustable) amount of time. When the alarm tries to turn off the siren (i.e. I hit the stop button on the alarm's remote), this will kill power to both the timer and siren. Doing so will reset the timer so it's ready for next time. I suppose I could also live with a timer that needs a manual reset using a button or whatever. Anyone know where I can get such a timer? This timer needs to be inexpensive, as I'm disabled and living off public assistance. Before becoming disabled, I was a computer science major at UC Berkeley, so I have basic electronics knowledge. My experience with soldering, however, is limited to a single light sensing switch I made. (That was a fun project, intended to operate a window shade that would open with the morning sun.) > Incidentally, I'm also > going to install a homemade fuel pump kill switch, but this won't be > connected to the alarm system. don't foget to wire the switc to the fuel gague too :) Bye. Jasen > don't foget to wire the switc to the fuel gague too :) To make it look like I'm out of gas? That might be a good idea... Also, I was thinking of putting a timer on the kill switch too. That way the perps will actually be able to get into traffic before the car dies on them, thus forcing them to abandon it instead of still having time to find the kill switch. Or, I was thinking of making it so applying the brakes kills the engine. This will make it look exactly like how the van used to actually behave when its fuel pump was on the fritz. 'Course all this is getting a little weird. Better K.I.S.S. and not mess up my only transportation too bad! I'm already kinda worried about the simple kill switch actually... like does it need a fuse? What about causing a spike? What amp and voltage rating does the switch have to be? Etc. Etc. I *just* put in a new fuel pump and don't want to have to do that again! (Or strand myself somewhere... had enough of that already.) Kanon (P.S. I'll look for info on the 555. Thanks!) >> don't foget to wire the switc to the fuel gague too :) > [quoted text clipped - 3 lines] > them, thus forcing them to abandon it instead of still having time to > find the kill switch. I did it to my first car, the carburettor held enough fuel for about 10 seconds driving, if your car is fuel injected then yeah a timer would be a good idea. > Or, I was thinking of making it so applying the brakes kills the > engine. This will make it look exactly like how the van used to > actually behave when its fuel pump was on the fritz. engine dies at the first stop light/sign :) sounds good. the fuel gague also gives the user a clue if they forgot to press the button for some reason > 'Course all this is getting a little weird. Better K.I.S.S. and not > mess up my only transportation too bad! I'm already kinda worried about > the simple kill switch actually... like does it need a fuse? What about > causing a spike? What amp and voltage rating does the switch have to > be? use a relay 10A contacts would be plenty, but 40A lighting reays are plentiful. > Etc. Etc. I *just* put in a new fuel pump and don't want to have to > do that again! (Or strand myself somewhere... had enough of that > already.) Before. ign +----> to other equipment switch | | >--oxo--+----------------------------> to fuel pump . . existing fuse. After. +--> | | --- hidden push-button +------o o---. | | | _-~ | >--oxo--+--o-~: 0---|----------+---> : | | |\~~|----+--+--|<---' | \ | | D2 | \|--.->|-' ~~~ | D1 | -+- /// when the button is pressed the relay turns on and pwers itself and the fuelpump. D2 stops the push button from supplying current to the fuel pump (which means a small push-button can be used) D1 eats the spike from the relay coil when the ignition is turned off (many automotive relays have this diode fitted internally.) when the ignition is turned off the power to the relay stops and the system is reset. Bye. Jasen > the fuel gague also gives the user a clue if they forgot to press the button > for some reason Ah, very true. For this, I guess I'd need two relays connected to the same switch, right? Thanks for the great diagrams! Do the diodes need to be a special kind? Ed, thanks for your diagram also. I can see this kind of timer coming in real handy! Kanon >> the fuel gague also gives the user a clue if they forgot to press the button >> for some reason > > Ah, very true. For this, I guess I'd need two relays connected to the > same switch, right? it depends on what you need to do to zero the fuel gague. relays are available with two sets of contacts ("dual pole"), one set could be responsible for the fuelpump and the other for messing with the apparent fuel level. or you could run a second relay off the output of the first. (or connect the coil in parallel with the first one's and get the same effect. > Thanks for the great diagrams! Do the diodes need to be a special kind? any general purpose rectifier diodes should be fine, eg 1N4000. Bye. Jasen > it depends on what you need to do to zero the fuel gague. Well, the fuel gauge is controlled by a potentiometer sending unit in the gas tank. Opening that circuit should make an infinite resistance, which will probably read as empty. I'll play with it. > any general purpose rectifier diodes should be fine, eg 1N4000. Cool, thanks for the info. First though, before any of this fancy stuff, I'm gonna just put in a simple kill switch. No relays or anything. I got a 30A switch that I'm going to connect to the fuel pump's inertia switch circuit (the inertia switch kills the fuel pump in case of a collision). Think this will need a protecting diode or fuse? look up 555 timing Circuits. Its a little chip that is in loads of timing devices. loads of circuits using a 555 on the net. All the best. look up 555 timing Circuits. Its a little chip that is in loads of timing devices. loads of circuits using a 555 on the net. All the best. http://www.kpsec.freeuk.com/555timer.htm > Hi, my car was just broken into yesterday, so I decided it's time to > get a car alarm. It's an old car, so I bought a cheap (but good brand) [quoted text clipped - 28 lines] > (That was a fun project, intended to operate a window shade that would > open with the morning sun.) I don't think you really want a delay between the time a vibration sensor is distrubed and the siren goes off. Normally, the kind of delay you want is a delay between the time you turn the alarm on, and the time it arms, to allow yourself time to get out of the car and lock the door. That prevents the siren when you shut the door on exit. Opening the dorr should not disturb the vibration sensor enough to trigger the alarm. There are many ways exit delay can be done. I'll show one that is the simplest and cheapest way, or close to it. The ACC line is a line that goes to +12 when the ignition switch is turned on. The +12 line is +12 regardless of the ignition switch. The circuit shown gives you roughly 10-15 seconds to exit the car from the time you turn the ignition switch off. +12 ----------------------------o o \ < Alarm on/off switch ACC --[.1R]--+-----+----+.... o | | |+ .+ | [Relay] [D] [C] TVS | | |+ | . | Gnd --+------+-----+----+.... [Alarm] | | +---- < relay contact | ^ normally closed | | | +-----------------------+ The relay is an Omron G6R-1-DC12 with a 655 ohm coil and contacts rated 5A at 30 VDC. D is a diode like a 1N4004. C is a 3300 uf electrolytic, which will give you roughly 10-15 seconds delay from the time you turn the ignition off until you turn the alarm on, exit the car, and lock it, before the alarm arms. You can put more capacitance in parallel to increase the time if you want. The parts are available at Allelectronics. http://www.allelectronics.com/ The cap is CAT #3300/25VA for 90 cents, the relay is CAT # RLY-428 for $1.75, and the 1N4004 is CAT# 1N4004 at 9 for $1.00. The .1 ohm 10 watt resistor is needed if you use the TVS, and is CAT #.1-10 at 2 for $1.00. You might want to add a transient supression diode - Mouser part #576-1.5KE22 - in parallel with D but oriented with (+) to (+) and (-) to (-) (D is oriented backwards). It's shown dotted in on the schematic as TVS. I haven't found the TVS necessary, but some insist on it. If you don't use the TVS, you don't need the .1R Ed On Mon, 26 Jun 2006 20:05:16 -0700, googlegroups wrote: (Incidentally, I'm also > going to install a homemade fuel pump kill switch, but this won't be > connected to the alarm system.) That should be all you need, and it's kewl - the car will run for about a block on the gas that's left in the fuel line and stuff, and then die in the middle of all of those witnesses as the thief tries to run away. ;-) Good Luck! Rich |
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