Help with timed 12v and 3v application...

Thread Starter

Jh5280

Joined May 24, 2019
3
Yes, a newbie to the forum but looking for some help with what amounts to probably a simple configuration based on what in read searching through the forums here. I'm looking for help and validation on a quick project I'm working on.

I have two devices that I need to pair in such a way that when I hit a button, I need a 12v circuit and a 3v circuit to be charged for say 5 seconds. There will be a switched 12v power supply (meaning it's battery powered with an on off switch on the battery pack). The 12v portion of the circuit will need about .8A while activated (so assume 1A with in rush). The 3v portion will need around 800mA.

My initial thought was a single throw single pole switch, a timed 12v relay of some sort, and a step down module to go from 12v to 3v for that portion.

So my question for the group is whether I'm on the right track, and if so, does anyone have suggestions on components? There are literally thousands out there. I would like the timed relay to have something like a potentiometer to allow for more precise timing adjustments if needed. Anyone know of a single small module that can do both? I found several small step down modules on Amazon but I had a hard time finding a relay module that allowed for the constant 12v supply with a 12v signal provided by the switch to activate the timer on the relay and switch the normally open circuit.

Thanks in advance.
 

Dodgydave

Joined Jun 22, 2012
9,169
Last edited:

Thread Starter

Jh5280

Joined May 24, 2019
3
How precise? A 555 timer won't give you high long term precision but should manage better than ~5%.
I'm basically trying to time a set of LED lights based on an audio recording, when hitting the switch, an audio track will play that usually lasts between 3 and 6 seconds. I'm not looking for ms type adjustments, so much as around second level adjustments.

Was looking at something like this (yes, pre-assembled) and stepping down the voltage for the audio circuit that needs 3v.
Amazon ASIN B00LWX9PPA. For some reason i can't post a link to the actual product on Amazon, but the ASIN will take you there.

If I do something like the 555, i'll need to find a super small board of some sort, all of this needs to fit in a really small space, roughly 2.5" diameter by about 1.75" high.

Thanks again for the responses.
 

Tonyr1084

Joined Sep 24, 2015
4,554
Tell us more about your LED configuration. I'm thinking there's a possibility you can use 3 volts for both the LED AND your audio signal. You might not have to use multiple voltages. But that all depends on a better understanding of what you're doing.

Is this just an indicator LED? Or is it something more substantial?

And just to point out a possible mis-print, you say you need 12 volts at .8 amps but your 3 volts needs 800 mA. 800 mA is the same as 0.8 amps. And LED's don't have an inrush current. At least I've never heard of such.
 

Thread Starter

Jh5280

Joined May 24, 2019
3
Tell us more about your LED configuration. I'm thinking there's a possibility you can use 3 volts for both the LED AND your audio signal. You might not have to use multiple voltages. But that all depends on a better understanding of what you're doing.

Is this just an indicator LED? Or is it something more substantial?

And just to point out a possible mis-print, you say you need 12 volts at .8 amps but your 3 volts needs 800 mA. 800 mA is the same as 0.8 amps. And LED's don't have an inrush current. At least I've never heard of such.

Thanks for pointing out the misprint. Yes, that's my mistake, I haven't actually tested the current draw on the 3V side, but based on the fact that its designed to run on two AAA batteries, it's substantially less than that. Most of the buck converters i've looked at had a 3A max rating on the lower voltage side.

So the LED footprint is actually kind of substantial, it's 12 fairly powerful LED's that are controlled by a small circuit board, the board allows a selectable, light pattern. The board and LED's combined, with all LED's on a steady burn pulled the .8A. I personally don't care if the LED's have a selectable pattern, but I want them to flash in a steady pattern (which is one of the options currently). On the board, I found several pins that were running around 4V (on several sides of resistors and a couple mosfets), which I tried using for the 3V function but for some reason it wouldn't work, my guess is those circuits weren't designed to supply the current needed.

Hopefully that helps.
 
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