School me on using electric "bucks" to control voltage?

[toximus]

I had an idea to double up the inputs on my LS swapped dash. The dash analog input can sense voltage which I can use to turn on indicator lights.

I'm thinking about using something like this: MPM3610 5V Buck Converter Breakout - 21V In 5V Out at 1.2A or this: UBEC DC/DC Step-Down (Buck) Converter - 5V @ 3A output

I only have the +12v indicator leads from the OEM TJ cluster connectors, so how would I practically wire this up? I'm hoping to learn something new!

 

[rattle_snake]

Buck converter - Wikipedia

en.wikipedia.org

but

Given your application you can just use 2 resistors to get 5v from 12v. The dash input likely needs very, very little current. Given the OR diodes aim for 5.7 to 6. 6 V is half so 2 resistors are same value. 1k and 1k will draw 6 ma and should be plenty to drive the input.

 

[Bebop]

You don't need headlight indicator.
Just tie the backlighting of the gauges to it.

If the gauges are lit, your headlights are on.

 

[toximus]

Buck converter - Wikipedia

en.wikipedia.org

but

Given your application you can just use 2 resistors to get 5v from 12v. The dash input likely needs very, very little current. Given the OR diodes aim for 5.7 to 6. 6 V is half so 2 resistors are same value. 1k and 1k will draw 6 ma and should be plenty to drive the input.

Like this?

You don't need headlight indicator.
Just tie the backlighting of the gauges to it.

If the gauges are lit, your headlights are on.

It's a digital dash with a light sensor for dimming.

 

[egdinger]

Not like that for the resistors, here's a page with more info, Voltage Divider Conversion Calculator | DigiKey.

 

[toximus]

How about now? 😬

 

[egdinger]

Yup that'll work. One thing I haven't seen mentioned yet is that with the engine/alt running your voltage will probably be higher than 12v, closer to 14.4v, meaning to voltage after the divider will be ~7.2v. But if you're running this into a programmable analog input it shouldn't be an issue.

 

[toximus]

Yup that'll work. One thing I haven't seen mentioned yet is that with the engine/alt running your voltage will probably be higher than 12v, closer to 14.4v, meaning to voltage after the divider will be ~7.2v. But if you're running this into a programmable analog input it shouldn't be an issue.

Perfect! Thank you so much!

Yeah, I can program in a voltage range. I don't expect there'd ever be enough voltage drop across the system either to overlap the ranges -- and if it does I probably have bigger problems than knowing if my headlights are on brights or dims.

 

[Bebop]

What dash are you using that you're out of I/Os ?

 

[toximus]

What dash are you using that you're out of I/Os ?

AiM MXG Strada. It has 8 inputs, but I'd be using them all. So by combining headlights it leaves 1 available if I want to add something in the future.

1. Fuel level
2. Brake (hand brake and shuttle valve)
3. Headlights on
4. Headlights bright
5. Turn Left
6. Turn Right
7. 4wd
8. Low range

Low range isn't something I need visually, but I can use it to correct displayed MPH.

 

[Bebop]

idea:

Aim Channel Expansion - Aim Technologies

Aim Channel Expansion BUY ONLINE Enhance Your Logger Performance The Aim Channel Expansion is a compact CAN device that provides virtually endless data acquisition system expansion options. The Channel Expansion hub adds up to four freely configurable analog (or two digital and two analog)...

www.aimtechnologies.com

If not, you can use the method above to share the Turn signal inputs together, as well as the 4WD and low range.

I'm also pretty sure the ECU has a provision for Low range (and maybe 4wd).

 

[toximus]

If not, you can use the method above to share the Turn signal inputs together, as well as the 4WD and low range.

I've been trying to think through that too, but I'm not sure how I'd be able to know if it's in 4WD or low range? Since the Atlas can be in 4WD but not low, or it can be in low but not 4WD. Turn signals wouldn't be too much of a loss if I combined them since it's not like I need the indicator lights to remind me which direction I flicked the stalk.

I'm also pretty sure the ECU has a provision for Low range (and maybe 4wd).

I'm hoping it does. Back when I bought the harness and ECU I remember something about it not understanding low range. Maybe because the E38 ECU is from a 2WD car? Idk what I'm talking about lol.

 

[toximus]

Here's what my harness builder (Jon at RPM Extreme) told me back when I bought it:

NO. There is no simple way for the GM ECU to know when it is in 4 low. The GM speed will read 3x or whatever ratio is in the t case higher.

This usually docent cause much issue as you are going slow when in 4 low.

 

[Bebop]

VSS in the output of the TCase.

More resistors for 4WD OR 4Low

 

[toximus]

VSS in the output of the TCase.

 

[Bebop]

Change the output and put one with the VSS