New Circuit Idea

I'm designing a simple circuit that adds to the functionality of the turn signals of my truck. I want it to be able to indicate which what I am turning no matter if the bulb is working or not. I need a way to keep from damaging the uC I plan on using with the full 12-14VDC of the electrical system of the vehicle. I thought about using transistors to act as switches for the 2 inputs for the built in turn signals, but I'm not sure. It has been a while since I was messing with programs to design circuits and even longer since I've been on here. I plan on simulating the circuit before I actually start building it so I can see if everything works the way it is supposed to. Can anyone give me a suggestion or recommendation for a good setup to use since I will be using automotive voltages?

skeeterb said:

I want it to be able to indicate which what I am turning no matter if the bulb is working or not.

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How?

Mike.

I plan on using LEDs for the indicators. Sorry for not informing y'all in the OP.

One of your main concern is protection from "load dump".





Regards, Dana.

skeeterb said:

I want it to be able to indicate which what I am turning no matter if the bulb is working or not.

Click to expand...

Do you mean monitor lights on the dashboard or whatever, or external LED indicators on the truck?

re. The MCU inputs, it's nothing that special, no different to inputs on industrial 24V gear. Just a voltage divider with two resistors to take the level down to around 5V, a small capacitor to 0V from that point to ground (across the lower resistor) and then a series resistor, eg. 10K, from that point to the MCU input pin to limit the current if it is above the device supply voltage.

For higher noise immunity you can add a zener diode in series with, or instead of, the upper resistor in the voltage divider.


For the device power, a filter with a low value resistor and both a fairly large electrolytic plus a 0.1uF plastic film or ceramic to catch high frequency spikes, then a switch mode regulator rated for at least 40V input, so it's not harmed by occasional spikes.

There are voltage regulators available that will stand load-dump voltages.

https://uk.farnell.com/diodes-inc/a...-3-3v-0-05a-40-to-125deg/dp/3518353?st=ap7384 It is rated to 45 V input

To protect against higher voltages, you can put a resistor in series and then a zener or transient suppressor to ground. It is a lot easier to limit the voltage to 40 V to protect regulators like the AP7384 than it is to limit to lower voltage for more usual regulators.

If you are wanting to measure an input signal, just use a voltage divider. A capacitor will reduce the transient voltages, and the input clamping diodes on the microprocessor input will prevent damage if you use 10 kOhm or higher resistors in your voltage divider.

Most vehicle will sense the current taken by the bulbs for turn signal, so if the bulb fails, the lamps will flash faster. I think that has been a requirement for 50 years or so, but there may be an exemption in the USA for vehicles that can tow trailers.

If your vehicle is sensing the current taken by the turn signals, you may need to put big resistors to take similar currents to the bulbs.

You are probably supposed to put some sort of sensing circuit for the LED lights, so that the driver can be warned if the LEDs fail.

skeeterb said:

I need a way to keep from damaging the uC I plan on using with the full 12-14VDC of the electrical system of the vehicle.

Click to expand...

Most car manufacturers work on 9 - 16 V range for normal operation.

Short term overloads include 1 minute at 28 V in the case of jump start from a 24 V vehicle.

500 ms of load dump, although that is often limited to 32 V or so by modern alternators.

-13 V for 1 minute in the case of reverse battery fitment.

rjenkinsgb said:

Do you mean monitor lights on the dashboard or whatever, or external LED indicators on the truck?

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All the indicators will be external. A LED strip on the tailgate and two smaller LED strips attached to the bottom of the side mirrors. I got this idea because I have had 2 bulbs burn out in the left tail light. Replacing the bulb is not an issue, but I want to be able to indicate the left or right turns if either of those bulbs burn out again. The only sensing it will do is whether the turn signal switch on the column is in the left or right turn position.

It sounds like what you want to do is add lights in parallel to the lights that are built into the vehicle. If so, that does not require a uC or any other electronics.

What are we missing?

ak

skeeterb said:

I need a way to keep from damaging the uC I plan on using with the full 12-14VDC of the electrical system of the vehicle.

Click to expand...

Take a look at 'transzorb' devices. Maybe something like this.

skeeterb said:

All the indicators will be external. A LED strip on the tailgate and two smaller LED strips attached to the bottom of the side mirrors. I got this idea because I have had 2 bulbs burn out in the left tail light. Replacing the bulb is not an issue, but I want to be able to indicate the left or right turns if either of those bulbs burn out again. The only sensing it will do is whether the turn signal switch on the column is in the left or right turn position.

Click to expand...

So...for example, under normal use, when you turn on the left turn signal, you want ALL the left turn lights (the left F/R bulbs AND the new left LED's) to flash?
And if either, or both, the left F/R Bulbs burn out, then the left turn signal will flash ALL the remaining left turn lights?