Custom microprocessor (Arduino, Pi, etc) Jeep project thread

[freedom_in_4low]

Conformal coating certainly wouldn't hurt, although we never bothered.

Shock/Vibration is relatively easy - secure everything. In another life I pre-qualified - I think it was eight - identical systems for NASA. The through hole components had to be staked in place with some kind of glue.

In general, bolt down or otherwise secure connectors if you're worried about them coming apart - that's why Jeep used those annoying little latches everywhere. Don't rely on PC grade connectors to stay in place without help. Blah, blah, blah.

What about where the wires connect to the board? They'll be soldered in, then fed through a hole in the enclosure wall where there will be a strain relief, but I probably need to glue the wires down within some distance of the solder joint to keep it from fatigue cracking, yes? Or is an inch or two of wire small enough to not be a concern?

In my industry everything is either screw terminals or crimped connectors. I know just enough here to overthink without knowing when I'm overthinking.

 

[Steel City 06]

My plan was to simply print an enclosure in polycarbonate with a generic gasket on it.

The Ruggeduino Mega I bought has the set screw terminals, so securing wires would be very easy. Not sure if that is an option in the version you're planning to use.

https://www.rugged-circuits.com/microcontroller-boards/rugged-mega-st-screw-terminal-7m4wd

 

[freedom_in_4low]

My plan was to simply print an enclosure in polycarbonate with a generic gasket on it.

The Ruggeduino Mega I bought has the set screw terminals, so securing wires would be very easy. Not sure if that is an option in the version you're planning to use.

https://www.rugged-circuits.com/microcontroller-boards/rugged-mega-st-screw-terminal-7m4wd

The board doesn't come that way but I could solder screw terminals onto the PCB board that will contain all my added electronics.

 

[Zorba]

What about where the wires connect to the board? They'll be soldered in, then fed through a hole in the enclosure wall where there will be a strain relief, but I probably need to glue the wires down within some distance of the solder joint to keep it from fatigue cracking, yes? Or is an inch or two of wire small enough to not be a concern?

In my industry everything is either screw terminals or crimped connectors. I know just enough here to overthink without knowing when I'm overthinking.

It would hurt to put "glop" on the wires at the solder connection - electronic grade RTV or similar. I don't know your exact situation - its probably overkill, but it won't hurt.

 

[freedom_in_4low]

It would hurt to put "glop" on the wires at the solder connection - electronic grade RTV or similar. I don't know your exact situation - its probably overkill, but it won't hurt.

overkill is my middle name.

 

[Zorba]

overkill is my middle name.

And not checking my post is apparently mine, I meant "It would NOT hurt..."

 

[freedom_in_4low]

And not checking my post is apparently mine, I meant "It would NOT hurt..."

Context clues got me there.

 

[freedom_in_4low]

PWM circuit?

I don't really know what resistance to use for the fan. And I probably need to learn up on how transistors work to actually select a resistor for R1. But CircuitLab says this does produce a correct 12V waveform inverted from the Arduino output.

 

[OldBuzzard]

That will probably work as is, but a typical circuit would have a higher base resistor (R1), perhaps 10K. Probably doesn't matter much, since you're using the transistor as a switch, and that should switch. 1K on the collector is typical, but you can go lower if you need more drive (probably not). For that type of circuit, you don't really need to go through the calculations, since it's used in lots of places with similar values. For a little more drive, you could switch to a 2N2222 or PN2222 transistor, but your fan probably has a fairly high impedance input and won't care.

 

[Steel City 06]

From a different SPAL guide I have on hand:

Edit: Note that this is a SPAL aftermarket fan, and I believe the PWM % logic is inverted in the OEM fans. Might have to test to be sure.

 

[Pascal25]

PWM circuit?

View attachment 569268

I don't really know what resistance to use for the fan. And I probably need to learn up on how transistors work to actually select a resistor for R1. But CircuitLab says this does produce a correct 12V waveform inverted from the Arduino output.

Fan motor inductance need any diode to protect the BJT? What amount of current does it draw? If too much for the beta of that transistor, could look at Darlingtons or a FET

 

[OldBuzzard]

Fan motor inductance need any diode to protect the BJT? What amount of current does it draw? If too much for the beta of that transistor, could look at Darlingtons or a FET

Joe's PWM circuit will be feeding the microcontroller in the fan controller. Fairly high impedance, very little current (mA or µA) to feed it. The fan motor will be handled by the internal circuitry, not from Joe's circuit.

 

[Pascal25]

Joe's PWM circuit will be feeding the microcontroller in the fan controller. Fairly high impedance, very little current (mA or µA) to feed it. The fan motor will be handled by the internal circuitry, not from Joe's circuit.

Good points

 

[freedom_in_4low]

I wouldn't put 12V into a microcontroller board, even if it says it can take it. They have itty-bitty voltage regulators which will run HOT. It might be best to regulate the 12V down to 5 to 8 volts to feed the Nano. And that gives an additional layer of protection.

something like an LM7805?

this one in partcular is rated for up to 125C and 35V supply voltage.
https://www.mouser.com/ProductDetail/Texas-Instruments/LM7805CT-NOPB?qs=OYMYEaN9QmBS2GvaX6GSkQ==

in the datasheet it shows this schematic with a couple of added capacitors...not entirely clear what problem those solve, and unclear how necessary they are given the notes below them. It'll be millimeters away from the TVS, does that count as the power supply filter? And being that I'll have a TVS, do i need C2 to "help transient response."


I probably knew all this stuff in 2005. But all of my electrical experience since then has been with 24-120V control circuits involving switches, relays, and contactors, and then 3 phase power and larger inductive and resistive loads up to 600V. The electronics involved in my work are entirely in purchased hardware that I basically get to treat like a black box - like programmable controllers and variable frequency drives.

 

[Zorba]

something like an LM7805?

this one in partcular is rated for up to 125C and 35V supply voltage.
https://www.mouser.com/ProductDetail/Texas-Instruments/LM7805CT-NOPB?qs=OYMYEaN9QmBS2GvaX6GSkQ==

in the datasheet it shows this schematic with a couple of added capacitors...not entirely clear what problem those solve, and unclear how necessary they are given the notes below them. It'll be millimeters away from the TVS, does that count as the power supply filter? And being that I'll have a TVS, do i need C2 to "help transient response."


I probably knew all this stuff in 2005. But all of my electrical experience since then has been with 24-120V control circuits involving switches, relays, and contactors, and then 3 phase power and larger inductive and resistive loads up to 600V. The electronics involved in my work are entirely in purchased hardware that I basically get to treat like a black box - like programmable controllers and variable frequency drives.

I haven't looked recently, but a few years ago drop in switch mode substitutes for 78xx regulators were a thing.

 

[OldBuzzard]

something like an LM7805?

Well, you could use a linear regulator like that, but it needs those capacitors, and a heat sink. I've built many dozens, but nowadays I use a cheap switch mode buck regulator, like @Zorba suggested. Look for a DC-DC Buck Converter Step Down Module which looks like this:

Sold by dozens of silly names on Amazon, a 10-pack costs about $12. They will regulate 3 to 35 volts down to 1 to 30 volts, at a listed 3 amps (but 1.5 amps max is more realistic). They run much cooler than the linear regulators. Put 12V in, and a suitable power resistor on the output to give it a load (1/2 amp or so is fine), and adjust the output voltage before you connect it into your circuit.

 

[Zorba]

Well, you could use a linear regulator like that, but it needs those capacitors, and a heat sink. I've built many dozens, but nowadays I use a cheap switch mode buck regulator, like @Zorba suggested. Look for a DC-DC Buck Converter Step Down Module which looks like this:

View attachment 569843

Sold by dozens of silly names on Amazon, a 10-pack costs about $12. They will regulate 3 to 35 volts down to 1 to 30 volts, at a listed 3 amps (but 1.5 amps max is more realistic). They run much cooler than the linear regulators. Put 12V in, and a suitable power resistor on the output to give it a load (1/2 amp or so is fine), and adjust the output voltage before you connect it into your circuit.

The ones I was thinking of were completely drop-in - they had the lead spacing of the linear regulator, but were in a plastic package a bit larger. This was years ago - maybe they don't make them that way anymore.

 

[OldBuzzard]

The ones I was thinking of were completely drop-in - they had the lead spacing of the linear regulator, but were in a plastic package a bit larger. This was years ago - maybe they don't make them that way anymore.

I don't remember seeing those. There are switching regulators in a TO-220 package just like linear regulators. But a switcher will always need an inductor and a couple of large-value caps, kind of hard to fit into the package.

 

[Zorba]

I don't remember seeing those. There are switching regulators in a TO-220 package just like linear regulators. But a switcher will always need an inductor and a couple of large-value caps, kind of hard to fit into the package.

They may have been current limited, I dunno. It was years back.

 

[Zorba]

This is what I was able to scare up :

Kinda-sorta-mostly a drop in replacement. 500ma current though, not 1 amp.

https://www.digikey.com/en/products/detail/aimtec/AMSRI-7805-EZ/24611607