PLX Automotive sensor -> LCD gauge

[rotordave]

Hi,

For a while now I've been trying to find a simple LCD gauge for my car that will display metric values from a sensor - unfortunately all the automotive gauges are designed for bling, and I want to make something myself that matches my car.

I haven't played with electronics since I was a kid, but since then I've done some intermediate electronics on my car and completed a computer science degree, so hopefully I can learn what I need to know.

What I'm looking at doing is getting an LCD panel like this one, some kind of PIC (which is still magic to me), and connect it (again through magic) to this PLX fluid temperature sensor module (that comes with a sensor).

That sensor module has both a digital output (with a well-defined spec) and an analog output. The analog output seems easier to use - it outputs a 0-5V linear voltage that maps to 0-150C. Though I'm sure there'd be much higher accuracy with the digital output.

So ultimately what I would like to achieve is to be able to program this PIC with my PC somehow (I'm a software developer so can write code) such that I can derive the degrees Celsius value from the voltage and format/update the display. I don't want to go as far as paging the display or anything, but it would be nice to later add another sensor data on the second row.

Or maybe I don't even need to buy the PLX device? I'm figuring the resistance from the sensor isn't necessarily linear with temperature, so that seems much more difficult.

So judging by my post, am I out of my depth? Or am I missing big chunks of the picture? Where should I look to next to learn more? I don't expect to be given all the answers (though that would be nice ).

Thanks for reading and hope you can help!

 

[alec_t]

Check the datasheet for the LM35. It's cheap (I suspect much cheaper than the PLX) and is often used with PICs for temperature measurement.
Try googling for PIC temperature measurement. I'm sure there's plenty on the net to help you.

 

[Reloadron]

This thread may fare better in the micro controller sections.

It is very doable. Pretty much a matter of how much you do (roll your own) or get off the shelf. As Alec mentions there are no shortage of PIC based temperature measurement solutions out there. The merit to building around an existing sensor is they easilt mate with existing automotive water jackets. The people in the uC sections could likely suggest a choice of PIC to use.

Ron

 

[rotordave]

Thanks for your replies. I had a look at the LM35, but I don't think thats what I'm after. I will be installing a temperature sensor in the water jacket that the PIC would have to read from. Also, I want to be able to add other sensor data, like oil pressure etc. So being able to use a sensor module like PLX (which come with sensors) would make it easier.

So the links I'm missing are between the PIC and the sensor module, and between the PIC and the LCD (which as I say is magic to me). I don't want to rule out using the digital output of the PLX device just yet (which btw sends sensor address/data packets at 100 mS over RS232) - I'm guessing this is fairly simple to program into a PIC through said magic.

So does there exist some kind of PIC on a board that connects to an LCD panel which I can connect over USB to program? Perhaps even without soldering?

Edit: Just found the LCD tutorials, need to start reading Hmm, on second thoughts, looks like I need an engineering degree for this.

 

[rotordave]

Maybe this is what I should be looking at?

https://electronics-diy.com/electronic_schematic.php?id=757

 

[Reloadron]

OK, with this in mind:

Also, I want to be able to add other sensor data, like oil pressure etc.

Here is what I would suggest you do. Start with listing all the parameters you want to monitor or for that matter possibly data log. I happen to be in the US so it would look like Oil Pressure, PSI, and the range. List everything, the parameter, engineering units, range. Next start looking at available sensors to measure the parameters. Once you have the parameters and sensors then you worry about signal conditioning the sensor outputs, for example scaling 0 to 5 volts for the sensor ranges. Once that is done, you can worry about a PIC and display. If you want to build a supervisory panel to monitor 8 parameters, part of choosing the PIC figures into that.

Just My Take
Ron

 

[Mosaic]

I recently designed, simulated, prototyped and built an automotive grade multigauge controller for turbocharged performance vehicles. I used an LED display since
1) LCDs respond slowly
2) LCDs tend to have contrast issues above 70 deg C exposure. Easily attainable in a black car in full tropical sun.
3) Decent transreflective, auto grade units are a bit pricey.

When designing for an auto environment you must consider the applicable standards for ROHS and Electromagnetic Compliance and Automotive load dump / ESD. Please read up on these before attempting your device or it can cause problems with other systems in the car via the power lines and I/O. Their are important design issues for managing EMC. Note also for proper compliance your device must tolerate 24VDC jump starts for 5 min max as well.

 

[rotordave]

I had a feeling it would be more complex taking it from breadboard to the car!

Mosaic, do you happen to have a spec/write-up for this project? Or is it IP for a contract you were working to?

Reloadron - initially I'm only interested in coolant temp, though Id like to use a 20x2 LCD character display which will give me enough room for coolant temperature, oil pressure & temperature, and EGT. PLX make the sensor modules for all of these, which come with the actual sensors, and have good documentation describing the signal conditioning (at its simplest it is division/multiplication, or for the digital output it also requires shifting bits etc). So I'm guesing that means I'd need a PIC with room for 4 inputs...

 

[Gobbledok]

Hi Dave I would be inclined to use the digital output from these sensors. It should be trivial with a PIC. Also, you can then daisy-chain the sensors and therefore only need one input to your magic chip

Oh and less wiring under your bonnet.

 

[rotordave]

I'd prefer to use digital too and you're right I'd only need one input then. The wiring would be under dash though.

So far, I'd describe it as anything but trivial

 

[Mosaic]

I own the IP.
So ask away.

BTW digital sensors make PIC I/O simpler

 

[rotordave]

I own the IP.
So ask away.

BTW digital sensors make PIC I/O simpler

Thanks for that. So what are the material implications for a circuit like this used in a car? I'd already guessed I'd need some sort of transformer to condition the voltage coming from the wiring harness. The car does have electronic ignition, so is there some design element I need to be aware of so it doesn't interfere with that?

And you got me thinking that I should use an OLED display instead. They look nicer anyway.

 

[Mosaic]

Automotive 5Vdc reg.

No transformer is required. A low drop out V-regulator like the LM2937 series and a staged suppressor to handle an Automotive load dump of 100+ Vdc spike for 5 ms. I used a unidirectional TVS backed up by a decent MOV and a current limiting 3W fireproof resistor .
See the pic.

The principle is the WW resistor limits the current draw and unloads the thermal loading from the LDO Vreg. The E-Fuse is for safety. The TVS clamps the spikes at around 49 Vc and the MOV comes in a bit lower around 42V. This permits the 1 ns response time of the spike suppression followed by the heavy duty load dump suppression by the MOV if the transient is long lasting.
The ferrites and the caps serve to eliminate 'noise' from the supply and prevent any feedback of the 8Mhz PIC switching from escaping into the wiring harness in order to help meet EMC standards. The LDO Vreg has it's own 60V auto shutoff for automotive use and can handle 24VDC jumpstart type voltages.

 

[rotordave]

You can appreciate that for someone who isn't an electronic engineer, pretty much all of what you said is gibberish to me. I suppose if all of that is really necessary, I'm out of my depth!

Is there not something off the shelf that would achieve that? It has to be a fairly common component?

 

[Mosaic]

have a look at this for a single solution.
**broken link removed**

Here's the datasheet with typical applications.
https://www.electro-tech-online.com/custompdfs/2012/01/4356fa-15.pdf

You'll note u have to add the Power MOSFET section depending on your expected load and you may require an additional regulator to match the requirements of the uC.
I found my application to be adequately supplied by the design I posted, which delivers regulation at 5VDC and load dump protection with a lower price point and the additional EMC handling with both an analog 5VDC and digital 5VDC for handling the isolation of the relay and solenoid drive circuitry which is part of the controller. Your app won't require isolated/filtered analog supplies since you are all digital.

The component cost of my design is around $3.00 in quantities of around 50 pcs. Which is better than the 'single solution' , especially when u have to add MOSFET drivers and additional vreg to the 'single solution', perhaps $6.00 bucks.

I guess there isn't a super simple solution. Mebbe i should make a module and sell it as a Sparkfun widget...but by the time a consumer gets it , it might be like $15 bux.

 

[rotordave]

Thanks for your post Mosaic. Every time I read one of your posts I feel further from the goal!

I saw in Reloadron's thread - PIC on Automotive Power - that if using an Arduino board, an "LM2940" is apparently sufficient for using that in automotive applications. In fact, the "programmer" types he refers to in that thread is pretty much what I am, I'd like to know what the resolution was for that. Which makes me think this thread should probably be in the automotive section.

Would it be advisable for me to take that approach? Buy an Arduino which would apparently let me program the on board PIC though USB and connect my serial input and LCD to that board?

 

[Mosaic]

The Lm2940 is the same family as the LM2937 used in the circuit I posted. The LM2937 - 5.0V itself it will give u reasonable automotive protection for gauge only (non critical) apps.

The reason for all the other components in my design is the controller that is being powered is NOT just a gauge and it influences the vehicle performance. Further it is intended as a commercial design , not a personal one. As a commercial design it must be robust.

As such, for your PERSONAL application, u can eliminate all but the following parts of my design: C1, C2, D22 and IC1. Is that simple enough? Just heat sink the regulator IC1 when u build it.

On the matter of the arduino it uses an Atmel AVR processor, not the PIC types.

Given your challenges with understanding the elctronic parts of the design an Arduino might be the easiest option for u, but certainly more expensive than building a dedicated solotuion.

My advice is to go with one of the PICKIT 3 programmer training kits, which comes with a prebuilt board (PIC) and go thru the tuts. Then check out Nigel Goodwins tuts and move on to building your app around the training board. When you are done you can then get a similar PIC to the one in the Trainer and build your debugged solution. By the time you are done with the tuts and your app design you will understand how to choose the correct PIC for your app.

Another good PIC tut resource is here:
**broken link removed**

Nice projects here:
**broken link removed**

Have a read on this, tells u why u need power protection when solenoids & relays are nearby (electrically):
https://www.electro-tech-online.com/custompdfs/2012/01/13c3311.pdf

Nice interactive electronic tuts for the beginner:
https://www.falstad.com/circuit/e-index.html