help with temp display for my Unimog

I forgot to mention that the Unimog has a 24 volt charging system but I could get or make (any help or plans for these) a 24V->12V converter. If it matters, I have a couple OLD laptops around that I suppose could be used as a display if someone told me how.

thanks aga>Hello everyone,

On a sunny day (Sun, 17 Dec 2006 20:50:04 GMT) it happened snipped-for-privacy@earthlink.net (doug) wrote in :

In case of a backup camera make sure the display can flip horizontally (mirror) and that will screw up any character generator display.

If we however have a 'flip' switch or input on that monitor, and if it accepts composite (NTSC or PAL), then I would:

Use an SAA5246A teletext chip to add text to the composite video from the rear view camera, but blank the text in reverse mode. Or use the SAA in standalone mode on the not flipped input.

Then use a small PIC microcontroller with 10 bit ADC and input mux, to drive the SAA5246A via i2c (text goes via i2c too). The SAA5246 needs an SRAM chip for display storage.

I have designed systems like that, driving i2c from the PC, for video subtitling.

It would require you to: understand i2c protocol, program a PIC in asm, build a board, make it car electrical system proof. Not for beginners.

A PIC16F819 has several analog inputs to read all of your sensors. The leftover lines are sufficient to run an LCD display (6 lines). You can put all of the readings on one 16x2 display at the same time.

Basically, 2 parts in its simplest form.

Luhan

This way may be more appropriate for your situation.

Get a meter that reads the thermocouple directly. Connect all of the negative thermocouple leads together at the negative meter terminal. Connect each of the positive leads to one pole of a rotary switch. Connect the common terminal from the switch to the meter positive.

Activate one sensor at a time by rotating the switch.

Luhan

O.P. should be sure to get a meter intended for the thermocouples being used (K type?) and one which has built in cold junction compensation otherwise readings will all be relative to the (variable) temperature of the common negative leads. The Omega Controls website is a gold mine for thermocouple information. If on a really tight budget, can use an ordinary panel DVM but K type thermocouple signal is only a few microvolts/degree C so amplification will be needed.Cold junction compensation can be roughly achieved by terminating the common t/c terminals on an aluminium or copper block and using an IC temperature sensor to measure the temperature of the block. Check National Semiconductor LB24 to get the idea but note that the LM321 is obsolete. Analogue Devices make a range of purpose built t/c interfacing IC's, but they aren't exactly cheap.

this sounds interesting. Looks like I'll have to do some poking around to learn a bit more. I'm a quick study, just wanted a few ideas to point me in a direction that I might be able to do. thanks

doug

It seems that the thermocouple idea might have some problems that I didn't know about. Cold junction this and that. Would a temp sensor from a car that varies resistance according to heat be more doable? there are several small 1/8" pipe thread, 1 wire, grounded body sensors that I could use and make fit instead. thanks again.

doug

Thermistor is the quick and easy solution. Its a tradeoff; the thermocouple accurate and rugged vs the thermistor, cheap and easy but not as accurate. Thermistors need bias current and their % resistance change per degree is much higher than the % voltage change per degree of the thermocouple. This makes them easier to use but the resistance change is not linear with temperature and calibration may change somewhat over life they are superb for relative temperature measurement but not so good for absolute measurements.The switching system that Luhan suggests can be adapted to work fine and you can buy a nice little bar or pie graph analogue display which will look at home in your vehicle and not fool you into thinking that you are making super accurate measurements. This might help:-

oops, sent in error without the url----

Thermocouples aren't that difficult to work with. There are some single chip devices that will do conversion and cold junction compensation with minimal additional component counts.

Once you have millivolt per degree F (or C) outputs, you can choose how best to display the data. On a video (or VGA display), an LED or LCD DVM module or whatever. Additionally, you can incorporate some comparators (or some tests in software if you use a cheap laptop) to raise an alarm if a parameter goes above a preset. This would be better than having to scan a bunch of readings manually while you are driving.

A laptop can do data logging easily, if this is any value to you. You could also do a backup cam with a USB camera on the same display. Used laptops can be found cheap and the programming is generally simpler than that for a microcontroller for a novice.

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On a sunny day (Mon, 18 Dec 2006 20:40:37 -0800) it happened "Paul Hovnanian P.E." wrote in :

Well, if you can tell me how to horizontally flip (mirror) without a lot of programming.

Use a viewer with a 'flip' option switch. I think xawtv has one (if one happens to be using Linux).

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On a sunny day (Tue, 19 Dec 2006 18:25:49 -0800) it happened "Paul Hovnanian P.E." wrote in :

I just types man xawtv, and no such option I see on a quick glance. xawtv is a pretty bad viwer IMO, I only use xine and mplayer. The mplayer manual tells me:

-flip Flip image upside-down.

This is not what we want, I knew about that feature. But there is indeed a mirror option: mplayer -vf mirror movie.ts

Now all text is reversed too :-). But the onscreen display is normal... probably subtitles normal too.

Anyways one could use a smaller window for the camera, and display the thermocouple values in a separate window.

So your idea would work.

But why use thermocouples? there are many nice i2c temp sensors.

Like I use here: ftp://panteltje.com/pub/mirror_plus_temp.gif

Display of my home (heater) control system. Now aint't that cool?

It also tells you how much you recently spent on kWh.

The display is written using xforms in Linux.

Xforms has a GUI generator (fdesign) that can generate C code.... Takes less then half an hour to make a little GUI interface like that. It has pretty good graphics widgest too. (Well you still have to write the drivers and build the hardware to get those temps hehe).

That's what I was thinking with the laptop. Lots of display real estate and good development tools.

The OP was using thermocouples and he might not want to change. Thermocouples can handle about any temperature one is likely to find in an engine. I'm not so sure about the sensors with integrated electronics. Once he figures out how to build one thermocouple module, that will suffice for everything.

Is that 10.48 Euro perday, per kWh or since the last billing period?

But the tools are there. If one needs a non-laptop solution, there are some one board systems with quarter VGA touchscreen displays. The app. developed on one's desktop can be moved over with (almost) no effort.

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On a sunny day (Wed, 20 Dec 2006 15:38:39 -0800) it happened "Paul Hovnanian P.E." wrote in :

Yes, been thinking about that, he has those but the interface is more complicated, small signals (see below too). If he just wants carter temp and gear temp, then he could pehaps glue some i2c based sensors or even si diodes (those work great as temp sensor, I fixed my washing machine temp sensor by replacing it with a bit of electronics and a si diode), i2C would directly interface to for example a par port.

Since I started it, some weeks ago, because of the extreme warm weather for November no heating was needed really. The equipment by itself is always good for +10 degrees centigrade over outside temp, so when it drops below 10 degrees outside I switch the thing on (switched it off in March). A kWh now goes for 6.21 cent last time I looked (excluding taxes). The system, apart from controlling on / off, also measures current, and calculates with that. Also had it running on manual some time, so that did not count, indeed went to computer after I payed the bills for this year. It turned out to not so much as aI feared :-)

Sure. On point : if you want to use an USB webcam, then in case of the car you may run into cable length problems? I do not know what exactly the max USB length is. I bought an analog color camera module for this:

You should expect up to 5 to 10 meters cable in a car.... I bought it for the motorbike, but it ended up in the front door of the house..

complicated,

based

machine

would directly

How about this?

or this for the really hot stuff:

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On a sunny day (Thu, 21 Dec 2006 17:05:47 -0800) it happened "Paul Hovnanian P.E." wrote in :

complicated,

i2c based

washing machine

would directly

Wow, cool, you cannot go wrong for 3$75 :-)

1024 Deg C should be enough for his engine :-) These are nice chips, I will bookmark that link.

complicated,

i2c based

washing machine

would directly

^^^^ Is this the new European price format?

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On a sunny day (Fri, 22 Dec 2006 18:36:32 -0800) it happened "Paul Hovnanian P.E." wrote in :

Well as 2R7 is so nice, I thought I'd push this a bit ;-)