Electronics > Beginners
Adding a horn on a delay: where to begin?
Rerouter:
I should mention most auto stores should have timer modules with a pot to set the delay.
Ian.M:
--- Quote from: vmallet on April 21, 2019, 02:27:58 am ---I see. As an alternative, could I limit the current by increasing the values of RH1/RH2 while keeping the ratio I was going for (and skipping the 1k)? Like 33K & 51K, or something in between? Is there a drawback in doing this?
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Yes, but the order of magnitude higher impedance makes it more sensitive to noise pickup and its also more sensitive to Zener leakage. Muntzing it to save one resistor isn't (IMHO) worth it.
I would suggest also adding a small capacitor across the Zener to filter out RFI. 10nF should do nicely. Otherwise there is a (small) risk of the horn triggering if an active mobile phone is near the control box.
@Rerouter: That's probably the right way to go if you are in the custom auto business, but the O.P. isn't going to learn much electronics from simply using an off-the-shelf module.
Doctorandus_P:
Whether you use an LM555, a 4017 or a microcontroller, when you want to build a reliable circuit the power supply section is very likely the most difficult to get right.
For example, automotive power supplies should be able to handle "load dump" situations, where the voltage can have short peaks of 80V.
vmallet:
--- Quote from: Ian.M on April 21, 2019, 03:32:07 am ---Yes, but the order of magnitude higher impedance makes it more sensitive to noise pickup and its also more sensitive to Zener leakage. Muntzing it to save one resistor isn't (IMHO) worth it.
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Thanks. I was more wondering about the additional voltage drop over the new resistor; but I've since then understood that given that the input pins have super high impedance, there will be effectively no current flow into the pin and so pretty much no voltage drop over the extra resistor. Makes sense.
--- Quote ---I would suggest also adding a small capacitor across the Zener to filter out RFI. 10nF should do nicely. Otherwise there is a (small) risk of the horn triggering if an active mobile phone is near the control box.
--- End quote ---
Noted. Would you have a short explanation of how that can happen? Or where to read about this type of interferences for a newbie? :)
--- Quote from: Rerouter on April 21, 2019, 03:05:19 am ---I should mention most auto stores should have timer modules with a pot to set the delay.
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Someone else mentioned this early in the thread but like Ian said, it's really all about learning. And I've sure learned plenty!
--- Quote from: Doctorandus_P on April 22, 2019, 04:26:14 pm ---Whether you use an LM555, a 4017 or a microcontroller, when you want to build a reliable circuit the power supply section is very likely the most difficult to get right.
For example, automotive power supplies should be able to handle "load dump" situations, where the voltage can have short peaks of 80V.
--- End quote ---
Have you taken a look at the latest schematic a few posts up? Could you comment on the current design of the power supply?
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