Two things...hardening homemade circuit and simple delay design

Thread Starter

Chopski

Joined Jan 17, 2016
17
Seriously. Some forums it's like pulling teeth to get answers to rookie questions. You all rock.

I am really excited to build this now. Hopefully I'll have time to go grab supplies tomorrow.I've modified the horn so that the compressor can be installed remotely from the actual horn resonator. There's not a lot of room so this allows some flexibility for installation locations.

Is silicon tile adhesive better than epoxy for some reason? Or just more economical or something?
 

wayneh

Joined Sep 9, 2010
16,286
Is silicon tile adhesive better than epoxy for some reason? Or just more economical or something?
The el-cheapo solution is fiberglass resin like you would use for car body work. It's cheap partly because of the volume used for that application - you can find it at Walmart. The silicone caulks without acetic acid are also a commonly used solution. Expanding foam polyurethane sealants also work. So does sand!

None of these home-brew solutions are as good as "real" potting compound if you look at things like thermal expansion coefficients, heat conduction, electrical insulation and so on. For your current application, I think you can get away with the cheapest solution you can find. It's intermittent duty, shouldn't generate much heat, isn't a "sensitive" design, and would be cheap to replace if it fails.
 

Thread Starter

Chopski

Joined Jan 17, 2016
17
So Gopher a few questions about in your circuit:

1. I think there's a diode? How do I select the right one?

2. And what is the function of the op amp? How do I select the right one of those?

3. Does this design not require a changeover relay? It looks like your design will leave the small horn firing when the large horn turns on?
 

GopherT

Joined Nov 23, 2012
8,012
So Gopher a few questions about in your circuit:

1. I think there's a diode? How do I select the right one?

2. And what is the function of the op amp? How do I select the right one of those?

3. Does this design not require a changeover relay? It looks like your design will leave the small horn firing when the large horn turns on?
The way I understood your earlier posts is that the smaller horn could stay on when the loud horn turned on. That way, you get a chord rather than a note - like a bigger car. It will give the errant driver the impression they are trying to change lanes and hit an Escalade rather than a Vespa.

Any diode standard diode will work. Common part numbers are 1N400x, x = 1 to 7, or 1N4148, 1N914. Essentially anything that is not a Zener diode.

The op amp acts as a comparator and you get a lag that does not turn the horn on at all until the capacitor charges to the set level (by the pot). Then it suddenly switches high (super high gain). A transistor does not have this kind of instant switching AND allow you to set the switching point.
 

Thread Starter

Chopski

Joined Jan 17, 2016
17
The way I understood your earlier posts is that the smaller horn could stay on when the loud horn turned on. That way, you get a chord rather than a note - like a bigger car. It will give the errant driver the impression they are trying to change lanes and hit an Escalade rather than a Vespa.

Any diode standard diode will work. Common part numbers are 1N400x, x = 1 to 7, or 1N4148, 1N914. Essentially anything that is not a Zener diode.

The op amp acts as a comparator and you get a lag that does not turn the horn on at all until the capacitor charges to the set level (by the pot). Then it suddenly switches high (super high gain). A transistor does not have this kind of instant switching AND allow you to set the switching point.
Yep this works just fine. I think someone else had proposed a circuit that turned off the small horn at the same time it turned on the big horn so I just wanted to be sure I understood how yours works. I think you're right that this will add even more dissonance to the horn note which makes it more noticeable. They might even think two cars are honking at them.

Roger on the diode. I guess there's not much to them? Just one way valves?

Thanks for the explanation on the op amp.

I'll hopefully get to put this together tomorrow and will report back with results soon.

Thanks again everyone.

EDIT: Is this (black thing with red stripe in middle) a diode?
part.png
 
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Thread Starter

Chopski

Joined Jan 17, 2016
17
The way I understood your earlier posts is that the smaller horn could stay on when the loud horn turned on. That way, you get a chord rather than a note - like a bigger car. It will give the errant driver the impression they are trying to change lanes and hit an Escalade rather than a Vespa.

Any diode standard diode will work. Common part numbers are 1N400x, x = 1 to 7, or 1N4148, 1N914. Essentially anything that is not a Zener diode.

The op amp acts as a comparator and you get a lag that does not turn the horn on at all until the capacitor charges to the set level (by the pot). Then it suddenly switches high (super high gain). A transistor does not have this kind of instant switching AND allow you to set the switching point.
Sorry, still need to know how to spec the right op amp.
 

GopherT

Joined Nov 23, 2012
8,012
Almost any common op amp will work.
TL082 is at radio shack, It will be fine.

I will prototype if for you tonight to make sure it works before you go out and buy anything.

RP Electronics has a bunch of options - just look under Components >> Semiconductors >> Linear ICs >>
TL081, TL082, TL084, LM358, LM324, NE5532,

All will be good. About$0.90 to $2 each (that is Canadian dollars - which is about the same as a peso, I think).

http://www.rpelectronics.com/electronic-components-parts/semiconductors/generic/linear-ics
 
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Thread Starter

Chopski

Joined Jan 17, 2016
17
Notwithstanding that the Canadian peso just takes a worse beating every day, I think I can afford that. But I will wait to hear your prototype report before heading down to the electronic pixie store.
 

GopherT

Joined Nov 23, 2012
8,012
Notwithstanding that the Canadian peso just takes a worse beating every day, I think I can afford that. But I will wait to hear your prototype report before heading down to the electronic pixie store.

Ok, minor change. The cheap and well-proven op amps they have at your local shop are perfect but require a slightly different transistor since these op amps do not reach the positive rail and shut off the transistor completely. So, instead of a darlington, you will need a MOSFET, I recommemd the IRF9540 for this application.
image.jpg
 

GopherT

Joined Nov 23, 2012
8,012
Ok, now I tried to make it easy on you with a grounded horn but the three little shops in Vancouver that have on-line parts lists do stock P-channel MOSFETS. Nor do they stock PNP darlington's (or any PNP with decent current carrying ability. So you are kind of out of luck for local stock. Rumor has it that Digikey.com ships to Canada with reasonable speed and, since they are practically in Canada, at a reasonable price.

Good luck. All tested well with the modifications shown in post above.

Let me know if you have any questions.
 

Thread Starter

Chopski

Joined Jan 17, 2016
17
Ok, now I tried to make it easy on you with a grounded horn but the three little shops in Vancouver that have on-line parts lists do stock P-channel MOSFETS. Nor do they stock PNP darlington's (or any PNP with decent current carrying ability. So you are kind of out of luck for local stock. Rumor has it that Digikey.com ships to Canada with reasonable speed and, since they are practically in Canada, at a reasonable price.

Good luck. All tested well with the modifications shown in post above.

Let me know if you have any questions.
Wow! Thanks Gopher! I'm going to drop by my local shop anyway as I think they don't necessarily have all of their inventory online and just opened a new location with much larger inventory. I might find what I need there although will check out Digikey as a just-in-case.

I should have time this weekend to put this thing together.
 

Thread Starter

Chopski

Joined Jan 17, 2016
17
Ok, now I tried to make it easy on you with a grounded horn but the three little shops in Vancouver that have on-line parts lists do stock P-channel MOSFETS. Nor do they stock PNP darlington's (or any PNP with decent current carrying ability. So you are kind of out of luck for local stock. Rumor has it that Digikey.com ships to Canada with reasonable speed and, since they are practically in Canada, at a reasonable price.

Good luck. All tested well with the modifications shown in post above.

Let me know if you have any questions.
I've got the board mostly soldered together, just need one more component that I forgot to pick up on the weekend. It was surprisingly tricky going from schematic to actually placing parts and figuring out how they have to be connected.
 
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