• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Automotive Ideas...

Not open for further replies.


New Member
Okay, I will admit I am a newbie to this forum as well as electronics as a hobby, but I understand electric theory well enough to get me in trouble. Only recently got interested into ICs etc. Introductions aside, please comment on my ideas:

1. A voltage monitoring device that will close three separate circuits at three separate voltage references. Primarily used to monitor 12v auto system voltages and have a "low" "okay" and "high" indicator. I'm researching into the zener diode arena, unfamilar with ICs that may be good for this. Thinking this should be a simple circuit design, what do you think?

2. Device set to switch at a set frequency (0-12k rpm >> 0-200 Hz). Any ideas?

I am into low-cost easy-to-access solutions. Thanks for your time!


Active Member
Worth mentioning is that auto electrical systems are incredibly noisy. I put a scope on the cig lighter on my 95 Beretta and was amazed at what I saw - wasn't a nice flat 13.8 vdc.

Don't want to spoil your fun but I bought a nicer version of what you describe - 2 sets of 3 leds - one set to use while running to indicate condition of charging system, the other to use while engine off to indicate condition of battery. Cost me $5 at Autozone. Plugged it into cig lighter and just left it there to see how things behaved. Helped me track down intermittent problem.

I've seen the homebrew versions implemented with zeners as you indicated. Nicely described in some Radio Shack booklets but I don't have a scanner so I can't share with you.

A caution on the RPM limiter - if you are really going to depend on it and use it on the street then test the daylights out of it to be certain it's reliable and fit for that service. Wrecking an engine is expensive. A surprise triggering while you are driving can be dangerous.

I am not able to offer much more help on the limiter except to say that if you choose some digital method be careful that the trigger is "all above" or "all below" a given setpoint. To trigger by comparing input to a setpoint so that it only triggers on "equal" would be unreliable - RPM, given gate time, might never exactly equal the setpoint so you could sail right on by the limit and never know it.


New Member
Here's an idea that uses a common philosophy. If the dual section - single IC feeding the LEDs is a concern, you could use the same idea with a different comparitor that has 4 sections on a single chip (using only three sections - each feeding a single LED). Do a search "battery monitor circuit" for more ideas.

Not open for further replies.

Latest threads

EE World Online Articles