Seat Belt Interlock Relay, Late 74-76’ - how does it work? Options

[Superhawk996]

OK. Been sidelined for a little while but time to get back to this insanity.

Thanks again to @JeffBowlsby @BdStone914 @Montreal914 for the parts to play with -- this would not be possible without you guys (IMG:style_emoticons/default/smilie_pokal.gif)

I've been working on reverse engineering the circuit and getting it put into LTSpice. Mostly for my own entertainment and education.

This little relay does some odd things which I mentioned earlier. LTSpice is confirming that some of the behaviors I'm seeing appear to be inherent to the circuit design and how it powers on. I haven't gone though them all but here's an example.

When the circuit first powers on (key on but not trying to Start):

If either of the seat cushions are occupied and a seat belt is fastened, the Fasten Seat Belt Lamp and the buzzer come on for about 1/4 - 1/2 second then shut off as power is applied. The vehicle start interlock relay engages and the vehicle would be allowed to start if the key is moved to start position.

I have two relays that do this but the time they are on varies between them. I suspect this is related to the fact that one relay, I've replaced the elecrolytic capacitors with new ones while the other one still has 50 year old capacitors in it.

The relay with the fresh capacitors stays on longer (almost 1/2 second) while the old unit is very short (like 1/4 second) but is noticeable.

I know this is a complete boondoggle given most of these systems have been either bypassed or completely disabled but I'm wondering if anyone else has a functional late (74' - 76') seat belt interlock system and wondering if others have seen this behavior from the lamp and buzzer.

[Superhawk996]

If there is interest, I’ll post more on the LTSpice model

Otherwise I’ll just get back to outlining the operation of the relay and the troubleshooting & repair of an in-op relay Jeff sent to me to see if we could get that working again.

[Superhawk996]

Here’s the situation where LTspice is capturing the Fasten Seat Belt lamp flash and brief buzzer at initial key on (but not yet trying to start).

In the model power is turned on at 5 seconds this is where the lamp flashes (green blip) then shuts off.

At 9 seconds the key is moved to the start position and the start relay is energized (red trace / yellow arrow).

Prior to modeling this circuit I wasn’t sure if this was something wrong with the parts I have or if it was inherent to the design.



Based on the two parts I have in hand and the LTSpice model, this appears to be the way the circuit is designed.

[Superhawk996]

So maybe it's an appropriate time to come back to what started this thread.

The buzzer on this seat belt warning system may be the most obnoxious sound known to man.

This whole project started off with a challenge from @Van B to replace the annoying buzzer with something that can play a MP3 song clip and to do it in a way that doesn't entail modifying the stock wiring.

I ended up finding a chip that can handle both the MP3 memory and also has a small audio amplifier built in that can drive a speaker directly.

The general idea here will be to disable the OEM buzzer and to incorporate this chip in its place. The chip isn't much larger than the OEM buzzer/relay. I'm hoping I can fit this inside the interlock relay enclosure somehow.

I'm still not sure what the end package will be but I'm thinking it's a little self contained project enclosure with the speaker that gets maybe just sits below the seat along with the interlock relay. We'll see.



The video below is a conceptual example of an MP3 sound clip that would replace the buzzer noise.


https://www.youtube.com/watch?v=YpBaGCLfcyI?si=vk36mfSeMDsXX30s


Still have details that need to be worked out since the chip operates on 5V instead of 12v but that can be handled with a voltage regulator or maybe even a simple voltage divider.

Anyway . . . hopefully that helps address part of why I started this crazy project.

The sound clip could be anything that is a MP3. Could be a song, a different buzzer tone, or a recorded voice telling saying buckle up assclown as a tribute to the voice synthesized talking Chrysler New Yorker of days gone by. (IMG:style_emoticons/default/stirthepot.gif)


https://www.youtube.com/watch?v=aW9nmuTqIE0?si=ulqVqpAfL9WfUM6A