Step Down Circuit help

Thread Starter

Doraonroids

Joined May 8, 2021
4
So, I'm replacing my head unit with a raspberry pi4 and a touch screen.

I plan to have a switch for running it off the car battery without a key. and some type of warning system to say if the battery is getting too low to start the car. The car would supply 12V 15 A on accessorie and 10 A without a key.

This will be place under a speaker so I'd like the noise to be minimal.

The pi4 needs 4.75 - 5.25 V and the ability to use 3 amps but I doubt it'll constantly use 3 amps. Since, typical bare bored uses 600mah, and I'll only be using a hifi hat and sometimes a BLE keyboard/touchpad(incase my screen doesn't work well).

The screen I'll be using would take 12V and 1.5 A. I assume I'd want a current limiting for this.

and I've been reading about buck converters for the step down powering the pi4.

Is there something else I should look into?

First post here:
Is it against the rules to ask someone to design a circuit board for me?
 

KeithWalker

Joined Jul 10, 2017
1,778
You have written about a number of different things in your post but you forgot to mention what you are talking about.
What exactly is the "head unit" that is the subject of your query? I presume that you are not planning on replacing your own head with a Raspberry-pi. That might look a little odd.
A little more detail, presented in an organized manner would make it much easier to understand what you are proposing to do and for us to make some constructive comments.
 

LowQCab

Joined Nov 6, 2012
510
He's talking about replacing his Car-Radio with an MP3 / MP4 Player based on
a Micro-Controller, that has a Touch-Screen-Interface.

The solution is to go buy one, they're dirt-cheap,
and they're giving them away down at
the local Gas-Station with a Fill-Up of Premium-Gas.

And with the store-bought version
you get a "Free" Remote-Control thrown into the bargain.

You can't build one cheaper than you can purchase one, and it will look like crap.

Or, get a cheap Tablet on sale at Walmart,
then buy a Headphone-to-2-RCA-Jacks Patch-Cord, and you're in business.
All the remaining Hardware is standard Car-Audio stuff.
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.
.
 

Papabravo

Joined Feb 24, 2006
16,104
It does seem that it is getting more and more difficult to build thangs that don't already exist. In search of the "thrill of victory", they invariably suffer the "agony of de feet", and "de hands" and "de wallet".
 

KeithWalker

Joined Jul 10, 2017
1,778
He's talking about replacing his Car-Radio with an MP3 / MP4 Player based on
a Micro-Controller, that has a Touch-Screen-Interface.
Then why did he not say that? It would have been much simpler.
In all of my very 72 years in electronics I have never heard a car radio referred to as a head unit. To me, that would be something in the outhouse!
 

Papabravo

Joined Feb 24, 2006
16,104
Then why did he not say that? It would have been much simpler.
In all of my very 72 years in electronics I have never heard a car radio referred to as a head unit. To me, that would be something in the outhouse!
From my years in the network business I though he was talking about a "headend" which received all traffic on one frequency and rebroadcast it on another. There is no on the obfuscation created by thinking and writing quickly. The faster you can type, the worse it gets.
 

Thread Starter

Doraonroids

Joined May 8, 2021
4
He's talking about replacing his Car-Radio with an MP3 / MP4 Player based on
a Micro-Controller, that has a Touch-Screen-Interface.

The solution is to go buy one, they're dirt-cheap,
and they're giving them away down at
the local Gas-Station with a Fill-Up of Premium-Gas.

And with the store-bought version
you get a "Free" Remote-Control thrown into the bargain.

You can't build one cheaper than you can purchase one, and it will look like crap.

Or, get a cheap Tablet on sale at Walmart,
then buy a Headphone-to-2-RCA-Jacks Patch-Cord, and you're in business.
All the remaining Hardware is standard Car-Audio stuff.
.
.
.
I need help with creating a step down circuit with input (12V 15A) and output (5V 3A) constantly within 4.75 and 5.25. but the screen takes 12V 1.5A. It will be sitting near a speaker so I'd like it to not have high radiation, not sure what the term is I'm looking for.
 

Thread Starter

Doraonroids

Joined May 8, 2021
4
You have written about a number of different things in your post but you forgot to mention what you are talking about.
What exactly is the "head unit" that is the subject of your query? I presume that you are not planning on replacing your own head with a Raspberry-pi. That might look a little odd.
A little more detail, presented in an organized manner would make it much easier to understand what you are proposing to do and for us to make some constructive comments.
A head unit is a car radio. I am replacing mine with a Raspberry-pi. But it needs power. I am looking for suggestions about creating a step down circuit with input (12V 15A) and output (5V 3A) constantly within 4.75 and 5.25. but the screen takes 12V 1.5A. It will be sitting near a speaker so I'd like it to not have high radiation, not sure what the term is I'm looking for.

Sorry, for the confusing post. Does this make more sense?
 

Papabravo

Joined Feb 24, 2006
16,104
A head unit is a car radio. I am replacing mine with a Raspberry-pi. But it needs power. I am looking for suggestions about creating a step down circuit with input (12V 15A) and output (5V 3A) constantly within 4.75 and 5.25. but the screen takes 12V 1.5A. It will be sitting near a speaker so I'd like it to not have high radiation, not sure what the term is I'm looking for.

Sorry, for the confusing post. Does this make more sense?
Find one that will work and buy it. It is called a buck converter.
 

Papabravo

Joined Feb 24, 2006
16,104
Does the number of output phases matter?
I'm not familiar with that usage. Can you describe what you mean by an output "phase".

Most of the modern switching regulators use a frequency that is 10x or more above the top of audio range of 20 kHz or so.
A DC-DC buck regulator is a really poor DIY project. It doesn't do well with typical prototype construction methods and really needs a competently laid our PCB (Printed Circuit Board). It also takes some skill to troubleshoot problems when things go wrong and it requires you to understand the design of power inductors in excruciating detail. You also need to be very picky with your capacitor selection. It's great to learn about them, but wait until you're not going to depend on the result working right away to dive into this particular subject. Try to find a vendor that will stand behind their product. You might be tempted to buy from eBay. I would resist that temptation for now. You have some expensive pieces on the output of this puppy. When you get the first one don't just hook it up to the expensive pieces. Get a dummy load made from power resistors to check it out first.
 
Last edited:

LowQCab

Joined Nov 6, 2012
510
Seriously Man,
if you have to ask for help with this,
you will not be successful at winding up with a working Micro-Controller project.

It's not as easy as it looks on YouTube, and you have a long way to go.

If you just have to try your hand at DIY,
there's about ~3-million listings on Amazon, Ebay, Walmart.com, etc., for Buck-Regulators.

If you want some really high-quality stuff to make your own DIY Regulator to blow-up,
just go to DigiKey.com.

I am qualified to build what you want to build,
but I would never even consider cobbling-up this type of project piece by piece.
The Market is flooded with thousands of inexpensive,
ready to just Plug-N-Play, examples of what you want to build.

But, of course, it's your money and time.

I'd advise you to start doing some serious research,
and start with some SIMPLE, BASIC, DIY projects first.
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