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Old 07-17-2019, 09:42 AM   #41
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Default Re: Running a microcontroller in car - power supply aspects

I am curious as to why the OPTO LED's side are not running of the regulator in your circuit. It looks like you are using OPTO as level shifter.
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Old 07-17-2019, 09:52 AM   #42
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Red face Re: Running a microcontroller in car - power supply aspects

Quote:
Originally Posted by budm View Post
I am curious as to why the OPTO LED's side are not running of the regulator in your circuit
This
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It looks like you are using OPTO as level shifter.
It's mostly out of commodity and to keep the car's circuit as stock as possible. 12v is present at the switches already, so to run off 5v, I'd have to cut the incoming power wires from the car's system to the switches and wire in my 5v line there, which of course would work, but I just don't want to alter that part. It's not a pleasure working on the wires in that dash - very tight in there, with wires going everywhere, so it has to be as plug and play as possible: connect it up then get out of there as quickly as possible
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Old 07-17-2019, 09:59 AM   #43
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Default Re: Running a microcontroller in car - power supply aspects

I see, trying to keep wiring as original.
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Old 07-17-2019, 10:53 AM   #44
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Default Re: Running a microcontroller in car - power supply aspects

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I see, trying to keep wiring as original.
Precisely.
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Old 07-18-2019, 01:39 AM   #45
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Lightbulb Re: Running a microcontroller in car - power supply aspects

Had another look over the schematic and made another change: the lock/unlock signals on the right now also have optoisolators (PC5 and PC6). This is actually how the circuit is currently set up on the breadboard, but I omitted those two for some reason. Trouble is, I can't add a protection diode there because those pins swing low/high when locking/unlocking. Basically those two wires I labeled there run from the ECU to the 4 actuators in the doors and 1 in the trunk and I need to somehow tap into them to trigger certain functions on the Arduino. It's a simple H-bridge inside the ECU that does this I THINK: when you lock the car, the LOCK pin gets 12v on it and the UNLOCK pin stays low. When you UNLOCK the car, the reverse happens: U/L pin gets 12v on it and the L pin stays LOW. I measured this to confirm. Adding a diode there would create a short, yet I still need to have some sort of protection there, since linear actuators create a ton of inductive kickback which overtime can kill those LEDs. A capacitor perhaps ?
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Old 07-18-2019, 09:33 AM   #46
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Default Re: Running a microcontroller in car - power supply aspects

Why would Low (Grounded) signal be problem? The MCU signals are ref. to GND. Am I missing something?
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Old 07-18-2019, 09:53 AM   #47
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Default Re: Running a microcontroller in car - power supply aspects

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Why would Low (Grounded) signal be problem? The MCU signals are ref. to GND. Am I missing something?
Actually you're right. I was thinking the pin would short out through the diode, because for some reason I mistakenly assumed the diode would go between the L and U/L pins themselves, which is not correct - it would go between EACH pin and GND, so when the pin is pulled high, the diode is reversed-biased and doesn't conduct and when it stays low, it's essentially GND, so no current flow either.

Another thing that confused me is the way those L/UL rails are laid out they look very similar to a split-rail supply, with GND being in the middle, L being let's say + and U/L being -, although it's nothing of the sorts, so that's another thing that threw me off, so you're right: diode across each of those LEDs and I should be good. Can't believe I screwed up on such a simple electronics circuit
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Old 07-19-2019, 12:19 AM   #48
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Lightbulb Re: Running a microcontroller in car - power supply aspects

Updated schematic. Added D6 and D7, plus a simple plot of the lock/unlock pins.
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