Hey guys , got a period , vintage hot rod I’m working in at work and customer has an odd request. they want a buzzer added to the seat belt circuit that buzzes unless you have it buckled. no biggie , but the belts on the hot rods they have are normally closed . Meaning , not buckled the switch is closed , bucked switch open . This is for the dash light . anyway to use these ‘ normally open “ seat belts to “ close” a circuit and have a buzzer . I know I can swap the belt and add a relay and some wires , just seeing if there is a simpler way . Reason I’m asking is I’m pretty lazy and customer is looking to have this modification done on all 250 of their “ hot rods “ they are purchasing off of us. So anything I can do to simplify things will be a plus . thanks
so the switch is "closed" when the belt is not latched and "open" when the switch is latched, is that what you are saying? That sounds like this is what you would want, No? Key on, belt not latched and the buzzer sounds, latch belt, switch go to "open" state and buzzer turns off. Maybe I'm not reading you right, or the first cup of coffee has not done it's thing yet.
Can be done , Curious to see what your solution will be, In how you would hide wires in both style belts shown .
it’s the opposite , switch is closed when the belt is not buckled , turns a light on the dash customer wants a buzzer to go off when the belt is not latched . Belts pictured are just for pics . I would be using a more “ modern style belt , with the switch in the buckle .
yup 250 “hot rods “ Most guys here know what I do for a living , it’s pretty close , not far off . The way I see info like this can be useful to any one at any time , And I don’t have a clue how to get this to happen at this point without installing a new seat belt and wiring from scratch Pain in the butt if you ask my lazy ass
Then they are exactly as you need them to be. Belt not done up - circuit closed - allows power through to power light and/or buzzer. Belt done up - circuit opens - kills power to turn off light and/or buzzer.
Don't modern cars also have a switch in the seat to tell when to turn on the buzzer? So it doesn't go off on the passenger side when no one is in the seat, or when the motor is running and the driver is not in the car..
I must be reading this wrong but swapping the light for a buzzer seems pretty straightforward. Even adding it in parallel to the light would work the way it is currently set up.
There are as many solutions as there are circuit designers. One KISS solution is one NPN transistor and a few resistors. Use transistor as an ON/OFF switch; emitter to ground, collector to buzzer, other terminal of buzzer to V+, base to belt switch, R1 base to V+, R2 base to ground. When belt switch opens, (V+) * (R2/(R1+R2) ) needs to be enough voltage to t.urn the transistor ON; so R1 high resistance, R2 low resistance, and R1 small enough and R2 high enough to let enough base current to flow to turn it ON. Belt switch closed must have very low resistance to drag the base voltage down close to zero volts. So you start by picking a common transistor, get the spec sheet, then calc some good R values. Excel is your friend, or freeware Spice even better. Unfortunately, you might find the simplest circuits react to electrical noise, so then you need to filter the supply and add a voltage regulator, limit base voltage, or maybe you build two of them and one works fine but the other needs different R values. Maybe it switches a couple times OK, but we didnt know the buzzer was inductive and we get a spike which kills our transistor so you add flyback protection... an ounce of test is worth a ton of theory. Making something reliable and cheap to manufacture that lives in the automotive environment is challenging, especially if I expect it to last many, many years after being out of production. (I think a lot of you may wish you had skipped all of the above.) Hmmm...switch opens turns something on...I might start by stealing errrrr reviewing schematics for some of those 1970s circuit designs which transistor-switched an ignition coil using the original points. Bet there is a cheap COTS coil driver out there. Will look, edit if I find. edit - Yeah, some of those old coil driver/solenoid driver circuits became IC's with IGBT outputs instead of bipolar transistors. One example still available is Fairchild (now ONSemi) ISL9V20240. Cheap in reel qty, 2 to 3 bucks in single qty.
Wire the buzzer in parallel with the light or if that circuit is inadequate to carry the load of the buzzer add a relay controlled by the light circuit. Those old seat belt buzzers were annoying.
From reading your post, I think @Pocket Nick has the easiest solution- add a small relay under the dash that powers the buzzer. Jump a wire from the light to the relay. Light on, buzzer on.
Since this will require a relay it's pretty simple. Just use the normally closed contacts in the relay to run the buzzer circuit so when the relays is powered with ignition on the buzzer operates. Then when the relay is energized it pulls in and opens those contacts.
My friends (75-77?) Ford Granada had this feature. Perhaps you could simply download a wiring diagram for that car and duplicate it.
Seems the fine folks have already provided the how. I'd simply suggest that you contact the belt manufacturer and ask them for their take on this. I would assume that if the belts already have a switch and you or your customer are buying 250 of them (!), they are either going to have a solution for this exact thing or can suggest one. I get the 'we want to build it in-house' thought process, but this is going to be a mini fabrication assembly line for a standardized setup and you will want some spares. Will a single assembly work for all? Is this something that can be offered back to the belt makers? I am not aware of your normal builds, so I don't know the reference.
I'm of the KISS clan, and you did say this is trad, so a simple circuit or a relay control is probably the best solution. If this is a beat it up, swap it out situation with more complex electronics, you might want to go down this path. I am not familiar with these, but they are common for electronic controls. How rugged, cheap and swap-able they are, you will have to research. https://www.ardumotive.com/how-to-use-a-buzzer-en.html
Weird electrical question? Really weird answer, and dangerously off topic! I've never heard a buzzer or warning device I could say I liked. I've just looked up programmable mp3 relays. Cheap as anything. Uses an mp file off your computer so you'd need to make that somehow. Imagine Marylin Monroe sultrilly saying 'hey Big Boy, I ain't going anywhere with you unless you buckle up'. Works for me but I'm a bit weird! Ymmv! Chris
@VANDENPLAS Dead simple. [no relays needed] You use a 5v 40mA piezoelectric buzzer with a 175 ohm resistor on the ground wire. Piezoelectric buzzer's are diodes and only flow current one direction The seat belt stalk has 2 wires. One wire is connected to a constant 12v [radio memory] the other wire is connected the cathode [-] of the piezoelectric buzzer Connect the anode [+] of the piezoelectric buzzer to switched 12v Connect the cathode [-] of the piezoelectric buzzer to ground [with the resistor in-series on this wire] Connect the seat belt wire to the cathode [-] of the piezoelectric buzzer between the resistor and piezoelectric buzzer ['T"d in] Now the scenario is 1: Ignition switch off , no power to the piezoelectric buzzer 2: Ignition switch off but seat belt plugged in , the piezoelectric buzzer only sees 12v at the cathode an only flows 1-way [so it is blocked] The seat belt 12v also sees ground but via the 175 ohm resistor [and flows very little current at 40mA] 3: Ignition switched on but seat belt NOT plugged in , the piezoelectric buzzer sees 12v + and a path to ground via the 175 ohm resistor . The piezoelectric buzzer will sound 4::Ignition switched on and seat belt plugged in , the piezoelectric buzzer sees 12v + on both sides [it passes no current through the piezoelectric buzzer] The piezoelectric buzzer doesn't sound.
Is that not what I said? the switch is closed when the belt/latch is not latched? I'm very sorry but I just want to understand. Maybe we are not talking the same language, electrical language that is. When I hear that a switch is in the "closed" state, I take it as the contacts are closed, connected or common and can conduct electric current. So if it is as you say, that the switch is closed when the belt is not buckled, that "closed" switch would turn on a light. But let's say I misunderstand and you mean the switch is "open" when the latch is not buckled. I would think you will need a relay, transistor or the circuit that KERRYNZL showed us. Do you plan on any type of seat switches? something to "arm" each seating position? If not, will you need to keep all seatbelts latched when the not in use? EDIT, I now see that these may be single seater cars.
What kind of “Hot Rods? are these? Pm me if necessary. You can get those buzzers for 12v too. EZ-GO golf carts use them for back up alarms.
@VANDENPLAS The main purpose for the resistor [post #21] is to prevent a dead short from the live feed from the seat belt. the piezoelectric buzzer is rated 5v-14v , so the resistor chokes it back to 5v A 80Ah battery powering a 40mA load will last approximately 2000 hours, or about 83 days continuous. I do these types of circuits often. On my friends 55 Chevy he wired in this funky relay system for a "lights left on warning" buzzer . I ripped it all out and used a simple 2-wire piezoelectric buzzer All I did was connect the anode [+] of the piezoelectric buzzer to the taillight circuit And connected the cathode [-] of the piezoelectric buzzer to the ignition circuit. With the lights on but ignition off the piezoelectric buzzer sees a path to ground via the gauges /oil sender On my O/T Toyota hybrid [the most stolen car in NZ because they don't have a chipped key] I put a "faux alarm" flashing LED by the ignition barrel. The anode [+] of the LED is connected to radio memory [constant 12v] The cathode [-] of the LED is connected to the USB charger port 12v feed [it sees ground via the charger] It flashes a red light all day and switches off with the ignition on.
So, there's an answer for how, but what about "why"? At least in the USA, seat belts have been mandatory in new cars for 56 years. Who really needs a reminder to belt up in any car, even an old one?
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