Oil Pressure Warning Alarm
 

I have been seeing a lot of discussion about low oil pressure alarms. It is a great idea. I just couldn't find anything I liked that did what I wanted. I guess I just wanted too much. Well, I finally came up with a system I liked but cost much more. I started with a micro controller that could be programed, can read dc voltages, etc. Designed some input circuits that would handle the 0 to 14V signals from the sensors. I wired it up to the oil pressure sensor, temperature sensor, fuel level sensor, battery voltage, and in my case an oxygen sensor. Integrated a 16x2 display, error light, buzzer and 2 switches. What I have now will monitor the oil pressure, temperature, voltage, fuel remaining, and fuel mixture. The error light flashes, and the buzzer buzzes 3 times if an error occurs. It delays errors for about 10 sec after the ign is turned on. The error levels can easily be adjusted to any thing you like. For instance now I have oil pressure set at less than 5 psi, temp at more than 212degF, voltage atless than 11.5V or more than 15.5 and fuel level at 1 gal remaining. If there is an error, the display shows which reading is bad. It even points at it with an arrow. In other words, if the alarm goes off, just look at the display and it will show you what the problem is along with the current reading. Oil and Temp are shown together, Voltage and Fuel together and O2 and some test data that can be changed are shown together. The O2 will not cause an error and the low fuel will only flash the error light but not the buzzer. One of the PB switches select the display page and the other resets the error for a few seconds and then beeps and displays the error if it is still present.
I have about $100 dollars and many many hours invested in it.
The first question I will answer is: No I won't build you one. I will however give you diagrams, programs, or anything else I have that you may need if you would like to build something like it. I will try to help in any way I can. This is not a project for some one who doesn't understand some electronics and computers but for people like me that enjoy building things like this and want to do it yourself. I know there are a lot of people out there that can do this, and do it better than I. Maybe someone would like to design a printed circuit board and make it available if someone wants to do something like this. That would make it a lot easier to build. Other things could easily be added or removed or changed.
What do you think?

Paul

You and Jeremy need to talk.

I'd set the oil pressure warning point closer to 1 bar/15 psi. Even that won't save you while cruising. Maybe your system can manage a second warning point of 3 bar/45 psi at 1500 and higher rpm.

While you're at it, how about a brake booster low vacuum warning? The tricky parts will be tapping the vacuum line downstream of the check valve for a sensor, and determining a warning point.

How to you manage multiple warnings while cranking until the engine settles at idle? It's only a couple of seconds for the 500 but it'll be a noisy 10-15 seconds for the 300 on cold mornings.

Sixto
87 300D^2

Yes, I need to increase the Oil Pressure Error to at least 1 bar. When I was writing the program, I just put in something above 0 psi. Next update I will fix that. Brake Booster Vacuum would be easy. Just get a MAP sensor from some old GM car (well, get a new one for some old GM car). Feed It into another ADC input, Write a little code and it is done. The Micro Controller has 8 ADC inputs of which I am only using 6 so far.
I have set a delay of about 10 seconds before it starts checking. On the 500, I could change it to 2 or 3 seconds and be fine. One thing the program does is average the last 5 readings, so it takes 5 readings to be stable. It reads all sensors about 3 times per second. Also, It reminds me that I am in the 500 and not the 300D. If I wait for the glow cycle when I am in the 500, it lets me know. So I will probably leave it at 10 seconds. I hope I am not the only one that drives both gas and diesel and wait when in the gas and sometimes I don't wait when in the D.

Any other improvements? The great thing about this system is a change only requires a little programing and it is done. Even adding a new sensor is reasonable easy now that the basic system is done.

Paul

That is easily accomplished with a Low Oil Pressure Warning Light type Sensor/Switch and a Buzzer.
That is what I did in the below thread:
Low oil pressure alarm for 617.952
http://www.peachparts.com/shopforum/showthread.php?t=214443&highlight=Low+oil+pressure+alarm+617.952

Perhaps the OP could use a separate from his system regular Low Oil Pressure Warning Light Sensor to take care of the low end of the Oil Pressure range and use the programmed range for the higher Oil Pressure.

The low oil pressure alarm is something that Sixto and I have discussed at length. Paul's system is ideal for such a thing because it is smarter than the simple sensors that previous posters, including myself, have used. Even with a 1.0 bar pressure sensor I still have occasion episodes when the alarm goes off even though there is no real problem (at hot idle, for example).

Paul, the problem is that at idle, Mercedes specs anything above 0.3 bar (~5 psi) is OK but at higher engine speeds the oil pressure must immediately increase. Your system is good because it can look at oil pressure and engine speed and do a couple of if/then decisions. For a uP-based system it is trivial. The ability to add other sensors and other conditions is a bonus. Paul, maybe you could find some hungry small manufacturer to build controller packages for you.

Jeremy

Jeremy, I started to put together a system like yours. It would be perfect. Then I thought, Well what about the temperature, I need to monitor that also. Then I remembered that Battery Voltage needed to be monitored also. There is nothing other than the battery light to tell you if there is a problem. Well, you get the idea. Well I thought about it for several months. We (Wife and I) retired at the end of Feb so I had time to really think about it. It was over kill but it gave me something to do.
Next time I have it out of the car (no big deal) I will add a tach signal and implement your suggestion of checking oil pressure at several different RPMs.

I don't think my 500 ever drops to 1 bar unless it is not running. But like you say, the more warning you get the better. I could look for anything less than 3 bar above 2000 rpm, at least 2 bar at 1500 and never less than 1 bar below 1000.That should cover it.

I'll let you know how it goes. We are planing a trip to Maine (from Matthews, NC) this month and I will get to the changes when we get back. That will give me 2000 miles to sort it out further.

Paul

Further on the "charge" light: all it tells you is that current is (or is not) flowing from the battery to the alternator, to power the rotor's magnetic field and thus generate a voltage in the stator. A voltmeter, OTOH, tells you the state of charge of the battery when you first turn on the key, while glowing (if diesel), while cranking, and then, after starting the engine, while charging.

Your uP-based system would also allow you to select from a number of places to measure the voltage -- at the battery itself, at a headlamp (to see if the load is dragging down the voltage, especially for lamps that exceed standard current draw), etc.

Finally, you could put a shunt in series with the main power lead (not the big battery lead but the one(s) that power all of the accessories; measuring the voltage drop (millivolts) across the shunt and having the uP convert it into Amperes would be easy, giving you an instant reading of the load on the electrical system as well as the current being produced by the alternator.

All of these things would not necessarily be things you would want to be staring at while driving (as bad as texting?) but would be great for diagnosing a problem and could be used, as you have already written, to trigger a trouble alarm.

Looking forward to seeing your results.

Jeremy

I am not sure whether the uP monitoring kit can prevent any real disaster if the oil pressure is lost. The kit needs to de-bounce erroneous signal and it is possible that the damage is done during the de-bouncing, gives an indication and you react to it to shut off the engine. However, it is better than nothing.

Personally I would not spend the effort and money to add something like this to the car. I presume you are using an uP like a 8051 with analogue inputs to monitor all the parameters. It is a lot of work and a lot of coding to do - C code? It is a fun project nonetheless.

Good luck.

Ah-Kay makes an important point: regardless of how the alarm is constructed and installed, the driver has to respond and get the engine shut down before damage is done. At 3000 RPM and 70 MPH on the freeway you have only a few seconds, I would suppose. [Anyone have hard data?]

Jeremy

Well we got back from Maine (Great trip, no problems, 20+mpg on highway, not bad for a 500SEL). I am using a ZX-24A ZBasic uP that programs in basic and using a 2X16 display. I can display 2 functions at one time. A push button switch advances it to the next 2 for a total of 6 (at this time). If there is a problem it beeps a beeper and flashes a light and displays the reading that is in error. The errors have priorities as follows. Oil pressure (4 levels of pressure/RPM), Temp at 212, Voltage as 12V and fuel level at 0 gal remaining. The low fuel only flashes the light but no beeps. I also monitor the O2 sensor (this car has a euro engine with no mixture control) so I can see how the fuel system is doing. That leaves 1 display position that I can change around as needed.
There is a slight delay between a problem and the actual alarm because of the buffering of the signals but it is less than .5 seconds. When there is an error the display points to the error on the screen so it doesn't take long to see what has happened. The great thing is it checks for errors 2 times per second. You can't possibly do better than that by just watching the gauges.
This is a big and time consuming project, but it was/is a lot of fun.
By the way, the oil pressure on my old 500 is always above 50 psi above 1500 rpm and never drops below 20 psi at idle in gear with A/C on after a 200 mile run above 70mph on a 95 deg day. No bad for an engine with 260K+ miles on it.
On the trip to Maine, one morning we started out and got in the interstate within 2 blocks of the motel. The system Beeped (scared the snot out of me). I looked and saw a temp error. I pulled over and stopped. By that time, the problem was gone. I think it may have been a bad connection at the temp sensor because the temp dropped instantly. However it did let me know the system was working.
Sorry for the long post, just wanted to give you an update and ask if there is anything else I need to improve my little toy.

Paul

PS If anyone is would like to see the diagrams and basic code, I could copy them and e-mail them to you. It is far too much to try to post them here. Also, if there is anyone as dumb as me and would like to build one, I would be glad to help. However, please don't ask me to build one for you.

To dig up an old thread i think i might have an idea that could solve the problem of a pressure switch with a high enough setting to protect the engine at highway speeds and not be sounding every time you stop in traffic.The switch i have in mind is sold as a Cat part and switches at 25psi(no.&nc.) which for most of our cars would have the alarm on at idle.So my new idea which will require someone smarter than me to work out is to find out how as many cars today have a switch somewhere that locks the doors when you reach 15 mph + or-. When our cars reach 15mph they should have more than 25psi oil pressure and the alarm circuit could be powered up.I admit that would not allow alarm protection at idle,but i would feel alot better with knowing that the alarm going on at 25psi would give a few seconds to get the engine shut off before destruction!
We are fortunate on this board to have some people smart enough to figure this out,write a how to and perhaps save an engine or two! Fingers crossed Don

Great find! Can you get us a Cat part number? There are probably several ways to implement this, depending on year/model/engine, etc. For example, the W124s have a speed sender on the speedometer. It's used (for example) to increase radio volume as the car speeds up. We have several folks on the forum who could build a circuit to activate an alarm circuit from that signal.

Jeremy

cruising at ~ 65mph and totally chillin, seat set back and reclined for cruise, music blaring, sunglasses for the bright sun, i was in a zone ...suddenly

noted what sounded like a shrill noise, prob a few secs went by while i wondered what it might be, it certainly got my attention

had a look at the gauges and oil pressure read zero, big time panic set in at the sudden reality

looked around a bit at the same time thinking, had to be careful with shutoff so the steering wheel wouldn't lock up, prob a few more secs went by

shut 'er off, made sure i had steering and mostly coasted to a stop, turned out an oil line blew

ended up with a knock otherwise engine was completely normal, did a temp repair and finished the 4 hr trip with mostly a mild cruise ~ 55 mph

i have read another similar account, forget the details but the oil took a dumping and there was no damage

Don and Jeremy,
I will give some thought to a vehicle speed or rpm switch but I think it may get hard to implement. In the cars that lock the doors and change volume of the radio, they mostly use body computers (GM), generic electronic modules (Ford), or some other form of computer. You probably remember the Gauge Computer I built for my 500. I think it would be the best way to do something like this. It could be striped down from what I did but could also monitor temperature, battery voltage, fuel level and just about anything else you want to monitor. The added things would cost less than $1.00 each and require only 1 more wire for each. I believe It could be done for $75 or so. The only requirement is that the gauges in the car have to work. I have a display but it is not necessary for your application. All you need is a buzzer and possibly a flashing light. The one time my 'alarm' went off I looked at the dash first and saw the problem. It was a false temperature reading. Right now I have 3 oil pressure checks at different RPM with a 4th of no alarm at less than 300 RPM. Would any one be interested in something like this? I know it doesn't fit in with 'Something cheap' but it gets hard to make something simple that will do what we need.
I'll let you know if I come up with something easier. I would recommend you think about using RPM instead of MPH. If a hose blows while starting off in 1st gear, you may not know it until you get up to 50 mph or what ever speed you use. That could be too late.

Paul

Jeremy
I just saw that you said 15 mph +/- but I still think RPM would be better.

I have some experience laying out single layer through-hole PC boards. With PC's nowadays, sure should be easy.

I would be interested in joining this project.