Running a microcontroller in car - power supply aspects

[stj]

Re: Running a microcontroller in car - power supply aspects

the pot is connected by default, there is a trace to cut if you dont use it

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

the pot is connected by default, there is a trace to cut if you dont use it

Are you sure ? I don't see any traces that need cutting, other than those solder pads on the back which were obviously not bridged out of the box until I did so, unless I'm missing something. The pictures on that Ali link show the underside too.

[redwire]

Re: Running a microcontroller in car - power supply aspects

What's a "green one"? They simply might have put the wrong resistor in there, to give 4V not 5V. Or the IC has a different reference voltage or is defective. What IC does it use.

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

THESE are the "green" ones There was a link the first time I mentioned them, but it probably got buried in the post and you missed it

[redwire]

Re: Running a microcontroller in car - power supply aspects

Ahh thanks I forgot which one you are using. That module uses MP2315 IC which has a low power mode set by a resistor to GND on pin 1. It's claimed to draw under 1mA and you get 10mA? I haven't tried one. You cut the tiny jumper?
This guy found it has an instability and he did some mod. for low voltage I think https://www.youtube.com/watch?v=yyrgW5dNUIo
I'll bet a bigger capacitors in/out would fix it.

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

Ahh thanks I forgot which one you are using. That module uses MP2315 IC which has a low power mode set by a resistor to GND on pin 1. It's claimed to draw under 1mA and you get 10mA? I haven't tried one. You cut the tiny jumper?
This guy found it has an instability and he did some mod. for low voltage I think https://www.youtube.com/watch?v=yyrgW5dNUIo
I'll bet a bigger capacitors in/out would fix it.

Yeah, OK, I never noticed the instructions when I got mine (the original link is gone anyway). I just assumed that track's just part of the board and is supposed to be there all the time, so I didn't mess with it, meaning I was getting BOTH the pot AND the fixed voltage resistors connected at once.....which means the same is going on in that monitor right now *fail*

Ok, knowing that, I'll probably give it another go and report back. Keeping the power consumption of this whole thing as low as possible is very important.

[stj]

Re: Running a microcontroller in car - power supply aspects

the mod i do on some is to replace the pot with 5k (original is something like 200k)
and cut that track - then solder a resistor across it i salvage from the top for 5v.

this gives me something like 5v-5.5v ajustment range!

[stj]

Re: Running a microcontroller in car - power supply aspects

btw, the best thing about these modules is the pinout and spacing matches 78xx linear regulators!

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

the mod i do on some is to replace the pot with 5k (original is something like 200k)
and cut that track - then solder a resistor across it i salvage from the top for 5v.

this gives me something like 5v-5.5v ajustment range!

Where does the resistor go exactly ? Across the track you just cut, so it's in series with the pot now ?

[stj]

Re: Running a microcontroller in car - power supply aspects

exactly, it's in series so you can fine-tune the resistance but only by 5k

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

Ok, I cut the track and indeed it works correctly now: bridging the 5v pads, actually gives me 5.1v, since the pot is out of the loop now. Still, the power consumption is 11mA...maybe it's related to that low power state on pin 1. I'm not sure these modules are suitable though because of the 24v limit of the MP2315 IC.

[redwire]

Re: Running a microcontroller in car - power supply aspects

MP chinese datasheets are misleading, they give quiescent current drain when the IC is off lol "VFB=0.9V" "Static Current 0.85mA" "97% efficient" trickery. Or the IC's are fake. All of these modules have too small in/out capacitors so they can go unstable. What a hassle.
The AAM Power Save resistor on pin 1 sets when it does pulse-skipping. It seems to be a voltage threshold.

Other modules MINI360 uses MP2307 340kHz, sync rectifier but this guy measured 41mA drain with 12V in and no load
Other modules use MP1584EN 1MHz, Schottky rectifier, max. 28Vin.

None of them are that great or beat an LDO, although some people got 3.3mA from your MP2315 modules, so it might have another problem?

I think the lowest TVS in a car would be 18V such as 1.5KE18A. They start to conduct 15.3V and at -40C they drop and start to leak current at 14.3V which is OK. They clamp to 25V with a big transient 59A which you could lower with a fuse having high resistance (an ohm or two) in series, which limits TVS current and it would clamp to less than 25V.

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

I think the lowest TVS in a car would be 18V such as 1.5KE18A. They start to conduct 15.3V and at -40C they drop and start to leak current at 14.3V which is OK. They clamp to 25V with a big transient 59A which you could lower with a fuse having high resistance (an ohm or two) in series, which limits TVS current and it would clamp to less than 25V.

This is good info. A TVS would go across the input to the regulator ? I think I'll stick with the larger LM regulators in the end, which can supposedly go up to 30v, but clamping to 25v would suffice I think...

[stj]

Re: Running a microcontroller in car - power supply aspects

spikes are spikes - very short.
just clamp them with a big mov

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

Just for those who are curious, here's what the project currently looks like on its perfboard The "power" section will go where that empty space is, opposite the optocouplers and the unused headers will be trimmed off, of course. 7 inputs, so 7 optocouplers: UP, DOWN, UP, DOWN (left+right), IGN. LOCK, UNLOCK.

[redwire]

Re: Running a microcontroller in car - power supply aspects

It looks fine to me, I have put far uglier builds in cars. They worked great until I hit a pothole lol. Just need a way to solder wires to the protoboard that don't flex and break.

I'm surprised we haven't beat the LM7805 yet for powering the board.

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

I'll take a shot of the back as well. The way I do it is leave as much of the component's lead as possible and bend in the direction I want to form a track and then solder over it, which ensures the leg of the component IS the track It's safer but can get ugly when you need to replace something....VERY ugly

I WAS thinking of a 7805 when I first started, but thought a switching regulator would be more efficient in the long run. Noise on the 7805 would still exist though, as I learned from a video of Dave. It doesn't quite help filter out the noise AFAIK, though probably less than the switching one.

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

Here's what the solder side looks like. The perfboard is janky, I know, it was a leftover piece that I just had to use to get rid of The leads to the left are the 2k resistors in series with the anode of the LED in the optocouplers and essentially serve as our "inputs" - when pulled to 12v, the LED turns on and the pin on the arduino is pulled low via the C-E path in the optocoupler.

The leads to the right are the 10k pull-ups which hold the pins high to 5v again - they'll all go to a "bus" rail when I get to that part.

The yellow wire is a GND wire which will be soldered once I sort out the layout of the power section....not sure whether I should go with the switching regulator or a simple 7805 as suggested....

[stj]

Re: Running a microcontroller in car - power supply aspects

clean the flux off, it's hard to tell if i'm looking at reflections or solder bridges!

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

clean the flux off, it's hard to tell if i'm looking at reflections or solder bridges!

Probably went a bit overboard with the lighting, but I can assure you there are no bridges Here's a hopefully better shot. This Galaxy S10+ that I'm using seems to have a lot of potential, but I can't seem to get stuff just right. Seems it's either too dark or too bright and not in focus....