Engine Monitor Help - Newbie
Kevin
Posts: 12
I am a newbie to microcontrollers, but have been a software engineer for many years.· I bought the StampWorks Experiment Kit and I'm having a blast building the experiments and creating a few of my own.
My real intent is to build a engine monitor for a airplane that I am currently building. It will monitor many aspects of the engine along with other things in the aircraft.
I am currently trying to figure out how to read from 6 Type-J and 6 Type-K thermocouplers using as few inputs as possible. The only chips I've found allow reading from one Thermocoupler and so having 12 would eat a lot of space on a board.· I would appreciate any ideas or suggestions.
Thanks,
Kevin
My real intent is to build a engine monitor for a airplane that I am currently building. It will monitor many aspects of the engine along with other things in the aircraft.
I am currently trying to figure out how to read from 6 Type-J and 6 Type-K thermocouplers using as few inputs as possible. The only chips I've found allow reading from one Thermocoupler and so having 12 would eat a lot of space on a board.· I would appreciate any ideas or suggestions.
Thanks,
Kevin
Comments
Being that you are building your own plane leads me to believe you have some inner knowledge in to backup systems.
Sorry parallax....as great as your product is, I'd be sure to have some back up systems.·(Depending what you're monitoring....fuel/oil are definates for back up monitoring).
Anyhow, that being said....There are multichannel ADC's out there.· The little dirty one I have has 4 inputs nad I'm sure you could probably find an 8input one.
Of course you could also use a MUX type of device (MUX=Multiplex).· A 4051 MUX chip would do the trick (I've attached the Nutz&Voltz article describing it).· The 4051 would only give you 8 inputs for 1 Stamp input (and 3 stamp control pins), but I'm sure you could gang a couple of these guys together.· Start with just the one....to see if it'll work for you.·
For you temp sensors, you'll need the ADC between the 4051 output pin and the stamp input pin.
I've just given you a quick little blast on this....for more detail on the hardware let me know....as for the programming: check the end of the article and they give some sample code.
I also think that you should read the datasheet on the 4051.· They also talk about the 4067 for a 16input interface.
Anyhow...this will get you a bit further!
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Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
i will break your question into two parts. first interfacing to the thermocouple (or other resistive device for that matter). i am not sure sure what chips you have looked at, but the Stamp can directly read a thermocouple using the POT command (BS1) or RCTIME (BS2 and up). from the syntax guide for the POT command:
"Read a 5 kΩ to 50 kΩ potentiometer, thermistor, photocell, or other variable resistance."
RCTIME has a similar wording. that said, i reference you to the BASIC Stamp I app note #7 (http://www.parallax.com/dl/appnt/stamps/bs1Appnotes.pdf) for a guidline of how to handle nonlinear resistive measurements. look through the Nuts & Volts articles for a BS2 version, i cannot remember one off the top of my head, but there should be a couple dealing with temperatures and RCTIME???
second managing the multitude of inputs. if this were a on/off signal i would recommend the 74165 shift-in register to expand your inputs (#23/#24 of StampWorks i think), however inputing an analog signal wont work with that. instead one approach is a multiplexer/demultiplexer chip. basically it acts like a digitally controlled rotary switch; see N&V#5 (http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv5.pdf)
that particular N&V example will gain you 8 lines at a cost of 3, but in your case that isnt good enough. so how about the 74HCT154 chip (just did a quick search at digikey) which is a 4-16 line multiplexer? using the principles from the N&V article, you will gain 16 lines for the cost of 4!
it is then just a matter of setting the mux to a channel and reading it in, then indexing to the next channel and so on. that should cover yer needs. 16 analog I/O for the cost of 4 control pins and 1 input pin while using 1 software subroutine to convert the temperature for you, and a bare bones minimum of board space. sounds pretty good to me. good luck and have a good one,
ross
could you use a pulse counter (BCD or otherwise) and connect it to a MUX and just use 2 pins off the stamp (1 for the count pulse and 1 for reset)?
this would be fine if he didn't want to check a specific temp on command.· If he just wants to cycle through the temps then this might be a better way to free up some more pins. (IF IT'D WORK!)
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Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Thanks for the information and suggestions. I've downloaded the referenced pdf's and datasheets and will study them.
I have to admit I never considered connecting the thermocouples directly to the Stamp. Actually, to be honest, I didn't know you could! However, that would eat far too many I/Os and I need them for other things.
I was looking at Maxim's Thermocouple-to-digital converters (MAX6674/6675) because they are simple and have integrated cold-junction compensation for more accurate readings which I believe I would loose if I connected the thermocouple directly to the Stamp. Problem is, these chips are all single channel. Would be great if they had a 12 channel converter!
Also, Maxim has several multichannel ADCs, but I didn't think I could connect a thermocouple directly to one. Again, thought I had to run through a converter to get accurate measurements.
I like the idea about multiplexing the inputs. I will certainly study that idea!
Anybody have experience with these MAX6674/6675 and do they provide more accurate measurements without the cold-junction compensation?
Again thanks,
Kevin
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Chris Savage
Knight Designs
324 West Main Street
P.O. Box 97
Montour Falls, NY 14865
(607) 535-6777
Business Page:·· http://www.knightdesigns.com
Personal Page:··· http://www.lightlink.com/dream/chris
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Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
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Chris Savage
Knight Designs
324 West Main Street
P.O. Box 97
Montour Falls, NY 14865
(607) 535-6777
Business Page:·· http://www.knightdesigns.com
Personal Page:··· http://www.lightlink.com/dream/chris
·
I do notice some ppl's posts look like black lettering on a dark grey background, which is hard for me to read and hilighting makes it easier.
but looking through the thread...all my posts are there and I can read them regular like.
IT guy....anything on this?
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Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
I too had trouble reading your post, but when I printed out the various replies, your text actually printed out instead of the black bars that appear when viewing.
Kevin
"<FONT style="BACKGROUND-COLOR: #000000">Being that you are building your..."
Which sets the background to black, and the text is already black, so you get black bars.
Just my 2 cents
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"OIOOIOOO OIIOOIOI OIIOIIOO OIIOIIOO OIIOIIII OOIOOOOO OIIIOIII OIIOIIII OIIIOOIO OIIOIIOO OIIOOIOO OOIOOOOI"
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Chris Savage
Knight Designs
324 West Main Street
P.O. Box 97
Montour Falls, NY 14865
(607) 535-6777
Business Page:·· http://www.knightdesigns.com
Personal Page:··· http://www.lightlink.com/dream/chris
·
Can you guys read my signature/tag?· Or is the entire post black?
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Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
All the other messages seem fine.· Very VERY weird.· But I'm using the Parallax skin and never saw it in the other one I used.
I'll have to start using the Preview I guess!
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Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
I'm seeing black bars for your post , but your tag line is just fine. I'm using all defaults and this seems only to have happened on your original reply. Odd...
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I used to be different, but now I'm the same...
If you do highlight my 'barred' post you can see the text....not sure what I was doing that might have caused it....
sb
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Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
This is how I see your sig.
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"OIOOIOOO OIIOOIOI OIIOIIOO OIIOIIOO OIIOIIII OOIOOOOO OIIIOIII OIIOIIII OIIIOOIO OIIOIIOO OIIOOIOO OOIOOOOI"
"Hey Klutch,
could you use a pulse counter (BCD or otherwise) and connect it to a MUX and just use 2 pins off the stamp (1 for the count pulse and 1 for reset)?
this would be fine if he didn't want to check a specific temp on command.· If he just wants to cycle through the temps then this might be a better way to free up some more pins. (IF IT'D WORK!)"
- ah, that is a very good idea to just scroll on through as long as he could live with losing the ability to skip/hold to a certain probe though.· may or may not be critical.
kevin said:
snip "However, that would eat far too many I/Os and I need them for other things."· snip "more accurate readings which I believe I would loose if I connected the thermocouple directly to the Stamp."·
-i think u may be missing how the mux works.· u should be able to to hook up all 12 probes w/ 4 lines·more at your disposal using the 74154, all for a total cost of 5 lines (4 control and 1 input).· do you need better than that?· if so, steves idea above has merit, or a variation off that.· if that still wont cut it, you may need to look at networking 2 Stamps togethor, or something else???
how much·temp accuracy do you need?· i would think that in this case, engine temp, fine precision into the partial degrees·wouldnt be needed but maybe i am wrong on that?· if not, then super fancy measurements would be unnecessary.· 1 last thing, for some more info on interfacing a thermocouple type device to the Stamp and using RCTIME, see page 55 and on in the Applied Sensors manual.· good basic info on interfacing a temp probe to a Stamp (http://www.parallax.com/dl/docs/books/edu/AppliedSensors1_3.pdf).
have a good one.
ross
I understand how the mux works now and will try it out. I'm putting a order in today for various parts, 74HCT142 and 74HC154 will be on the list. Don't know which one I will need, so I'll order both.
I'm interested in what steve wrote about using a pulse counter, but not sure how it works. Back to the stamp books! I bought the StampWorks kit that comes with the NX1000. I noticed that all the stamp books use the BOE board. Should I invest in one or is the NX1000 sufficent to work the various experiments? I plan on spending time on some of the AppliedSensor experiments.
I will be collecting input from approx 30 inputs. However, I should be able to multiplex many of these together such as the EGTs and CHTs which account for 12. However, I want to be able to provide serial interface in so I can update the program on the stamp along with providing another serial connection for stream data out to other devices. I also plan on attaching a LCD is the size range between 6.5 and 8. Currently looking at Promate and Kyocera. Don't have a clue yet on how to connect to a video driver for one of these yet...more research! Can anybody point me to some samples??
So, reducing the number of inputs lines is essential, thus my curiousity for steve's idea.
Here are some of the other sensor inputs I need to interface:
Fuel Flow (Flow scan sensor)
fuel level (L/R/Aux tanks)
Fuel PSI
Oil Temp & Oil PSI
Volts & Amps
Carb Heat/Turbine inlet temp (TIT)
Water PSI and Coolant Temp
Real-time clock to be used as a hobbs meter
RPM
Manifold pressure
Various position indicators for Flaps, Elevator trim, aileron trim, rudder trim
Landing Gear position - up/down & locked
Part of the challenge is getting the specs on these sensors. Some of it is published, others I will have to request from the manufactures.
Always looking for ideas, suggestions, and comments.
Thanks,
Kevin
after reading your last post, i had one last thought for you and a correction.
1st the correction. i do not believe that the 74154 i previously cited is the correct chip for this job. it is a 4-16, but it is only a demux/decoder which i did not catch on my original quickie search. in looking at its data sheet last night for another possible project of mine, it dawned on me that that particular chip had no data routing line (it only sets a given output given certain inputs)....oops. however, the CD4067 16 channel mux/demux is a correct chip. pull the data sheet from digikey, note that pin 1 is the common in/out pin - that is the data routing pin which the 74154 doesnt have. i apologize for that confusion.
ok, so now you need ~30 inputs.....how about this: 6 stamp lines and 3 chips for 32 I/O? we can take 2 - CD4067s and tie their "binary control inputs" (pins 10,11,13,14) togethor and then each to a Stamp pin, we can also tie togethor their bi/directional data lines (pin 1) and send that to its own Stamp pin. lastly, using the inhibit pin (pin 15) we can select/deselect each chip - a high on pin 15 will deselect that chip. we also want to tie these togethor but with 1 difference. you need to put an inverter like the 7404 in between to only 1 of them. the inverter will ensure that each chip sees a different logic level and thus enables either chip A or chip B to be on, but not both to avoid conflict on the lines. the inverter thus saves you an additional Stamp line. as long as you keep straight with which chip you are on and which input you are looking at, this should work for you.
if needed, this could be expanded to other chips by ditching the inverter and using additional Stamp lines or maybe a 3-8 decoder to select/deselect the various chips. note, that the decoder/demux from my original post could be used here, as you are only setting lines.
also, you never mentioned which Stamp you were using, but you may save yourself a bunch of headaches with resource (memory/speed/I/O) by jumping over to a BS2P-40. time for lunch....................................
ross
I caught the mistake a couple of days ago, but appreciate you double checking. I did come across the CD4067B that appears to meet my needs, but I haven't ordered it yet.· There are several different manufacturers and I don't know which to order from or if it doesn't matter. So, I waiting until I get my complete shopping list and than order from who ever can fill the majority of my order. I too considered using multiple 4067Bs to handle more inputs, but didn't know how to actually do it. In fact, I was doing resesarch to do just that. Your comments couldn't have come at a better time. In order for clarity, is this correct?· 4 I/O lines will be used as a selector for the multiplexer. The 5th I/O line will be connected to pin 15 on both 4067Bs, but through a 7404 inverter in order to make sure that only one 4067B as a high on pin 15 at a time. Currently, I am using the BS2 that came with my StampWorks kit. However, I was figuring on using the BS2p-40 in the end. My NX-1000 that came with the StampWorks kit only supports the 24 pin so I will either have to purchase the NX-1000 24/40 or· BS2p24/40 demo board. Sort of leaning towards the NX-1000 24/40 because of all the features·in displays for testing.
My plan is to continue testing each sensor individually in order to confirm my design and programming. Once I test them all, I will need to test as a whole. I am concerned about how fast I can read inputs through so much multiplexing. Not sure what speed penalty I'll have to pay.· Ideally, I want to hit all sensors at least once a second and still be able to·stream the data out a serial interface to a display module. Currently thinking about using a small SBC (single board computer) with a video interface to drive the 6.2" LCD to graphically depict the engine data.· Couldn't figure how to use a stamp to interface with a video controller, so thought·using a SBC·would be a quick solution for driving a display. The stamp module will collect the sensor data and the display module will display it.· I can develop/test the software for displaying the data on my PDA before deploying to the SBC.
Got another dumb newbie question. What can I use to simulate a thermocouple and thermister? Will a·potentiometer do the trick? I'm looking for a substitue for actually hooking up these sensors in order to test read through the multiplexer. I have the specs for the CHT sensors that tell me the temp -to- ohms comparison. For the CHTs, temp range is 80-300F and ohms are 4673-101. I told you I was a newbie!
Again, thanks for the followup. This forum has been a great resource for newbie to electronics like me who take on challenging projects!
As usually, I really appreciate comments or suggestions from anyone. As I make further progress, I'll be glad to share what I've done.
Thanks,
Kevin
"4 I/O lines will be used as a selector for the multiplexer." - yes, 4 total lines, just tied togethor.
"The 5th I/O line will be connected to pin 15 on both 4067Bs, but through a 7404 inverter in order to make sure that only one 4067B as a high on pin 15 at a time." - yes.· that pin, when high, esentially removes that chip from the circuit.· so you set which chip you want active, then your control signals on A,B,C,D will only effect that particular chip, and thus only route THAT 1 signal through.
you made no mention, but the sixth line for clarity is both data lines (pin 1) tied togethor.· so a total of 6 lines consumed from the Stamp.· i even whipped up, a very crude : ), MS paint drawing that should provide further clarity, it should be attached.
i think that you can safely piecemeal your project togethor on the BS2, but for the final you may want the BS2P40 depending on how many other things you want to do.· or you may just want the BS2P24 for the speed and memory.........
"I am concerned about how fast I can read inputs through so much multiplexing" - well, it really isnt that much multiplexing to tell you the truth.· off that, Stamp instruction timing isnt "exact".· the BS2 is ~4000 instructions/sec·(0.25ms/instruction) and the BS2P24/40 is ~12000 instructions/sec(.083ms/instruction), but each instruction varies a bit.· but as a pretty good·estimate you can basically count the number of instructions needed to perform a given task and multiply by the timing, then include instruction timing parameters (pause, etc) and arrive at how often you can check that sensor.· for timing critical applications, there are more accurate ways (o-scope for example) to determine time through a set of code.· if this is the only task for the Stamp, i would think (a bold statment indeed)·you could read, compute, format, and output the sensors data every second.· as a time saver, you would not need to display the data after each read, but rather as perhaps a batch all at once.· in other words, take a reading and compute it, and store it to memory.· repeat· till all 30 are read.· now send out all 30 as a batch to the host for display.· the host then parces the preformatted data string for display.· just a thought if timing got to be troublesome.
"What can I use to simulate a thermocouple and thermister? Will a·potentiometer do the trick?" - yes.· a thermocouple is a variable volt/current device while a thermister is a variable resistance device.· depending on how you arranged you circuit, a pot (variable resistance)·should work for either.· i think in the N&V article i referenced early interfaces to several pots through the mux.· a solar cell could also provide you with a variable voltage/current source in place of a thermocouple.
ross
Thanks for the drawing! I reviewed N&V#5 and saw how several pots were used through a mux. I went to a local store and bought a few 5k and 1K pots, so all I need to do is wait for my multiplexer to arrive to test.
Regarding packaging of data, I was planning on reading from all sensors before sending off a packet of data. So, I'm hoping to be able to read from all the inputs, do a little bit of computation, package the data and send across the wire within 1-1.5 secs. If this can't be done, then I'll look at spliting the inputs into separate read passes and only including inputs such as RPM on every pass. RPM is one display that you want to be pretty responsive to throttle changes.
Thanks,
Kevin
If you are interested in RPM measurement for R/C airplanes, download the video here: http://www.parallax.com/html_pages/resources/videolibrary/resources_product_videos.asp
It is titled "Remote Controlled Airplane BASIC Stamp projects". One of the projects is a twin engine synchronizer. It uses the QRD114 infrared sensor on the back of the nose cone - half of it is marked black and the other is stock aluminum. I can get the code for this but it was quite simple and used either COUNT or PULSIN to get RPM.
Ken Gracey
Parallax, Inc
Cool video! I was a avid R/C flyer years ago, but I managed to upscale to ones that I can sit in! I do have a couple of electric ones that I'm using to teach my 7yr old to fly. It's amazing how fast these kids can master eye to hand coordination!!
For my project, the tach sensor already exist and I only need to interface with it and display the RPM value. I'm currently working on interfacing with the CHTs/EGTs, so I haven't gotten to RPM sensor yet. If I run into trouble, I may ask you for that code!
Just a wild shot, but are there any examples of reading from a flow sensor to get GPH and totalizing?
Kevin