On-the-Go Slope Measurement

[IamIan]

Originally Posted by niky

The Racelogic V-Box gives you altitude readings in diagnostic mode, accurate to a tenth of a meter or so, given a good signal and an external antenna.

But it's a squiggly little number on a diagnostic screen full of satellite tracks, GPS time, latitude and longitude coordinates and etcetera.

That's another good option ... just do a change of altitude as a comparative slope.

[Occasionally6]

Originally Posted by jeff88

I can't seem to find one that is an analog output. The MPU-6050 says "I2C Digital-output of 6 or 9-axis MotionFusion data in rotation matrix, quaternion, Euler Angle, or raw data format". Is the 'raw data format' not analog?

Other than superseded Sparkfun boards, I couldn't find one either (but I haven't looked particularly hard for one). Maybe you will have to use two separate (analog) boards or figure out how to use the I2C.

My interpretation of "I2C Digital-output" is that the output is only as I2C.

What about this one: L3G4200D It says it has the option to output in SPI. I've tried looking that up, but can't find if it is analog or digital. Would SPI work for me?

It's not something I have done but Arduino can use SPI:

Arduino - SPI

What does the wattage rating mean? Is it the max watts the resistor can handle? So if I happened to buy 1W, that would work (just be a little overkill)?

The power that the resistor can dissipate. Use P=V x I to get the power in Watts. V is the voltage dropped across the resistor. To continue with the earlier example, 5V supply, 3.3V dropped across the LED, 30mA current limit, no other voltage drops in the circuit:

P = (5-3.3) x (30/1000)

P = 0.051W

1W will work. What you may find is that not all of the standard resistances are available in each of (1/4, 1/2, 1W) the low power resistor types and 1W
will likely have a wider tolerance than the other types of resistor.

OK. As a side note, how does it determine the speed, the size of the wavelength?

Exactly that. At 50% duty cycle the time spent high = the time spent low so measuring the time spent high and doubling it gives the wavelength, which can be converted into a frequency.

There are a couple (that I know of) frequency libraries for Arduino around that makes it a bit easier to implement than doing it from scratch.

So something like this then?:

That looks good.

I was looking for a DMM on Amazon and of course, about a million different ones came up. I want an inexpensive one, but is there something I should look for?

At a minimum it should have that >10M Ohm impedance, other than that...

On a car most of what you will use it for is DC voltage and less than 20V.

Duty cycle is nice to have, as is a tach. function. DC frequency is a workable proxy for the tach. and vice versa (you can convert from and to a frequency using a low tension ignition signal and the firing frequency of the particular car, or from a sensor signal).

Some ignition, wheel and road speed sensors do put out an AC frequency signal so that would be useful also.

3.5 (0-1999) or 3.75 (0-3999) digits is enough.

Somewhere between $20 and $60 is probably about right.

Any idea on what size veroboard I will need (approximately)? Would a 2x3" board be big enough?

It depends upon what you want to mount on it. I'll attach a circuit board image for a dual 7-segment display as an example. (Also, a schematic of a display circuit using the 4511. The resistor values are typical but you should check them for yourself.) A good standard hole spacing to use is 0.1". 5 holes (with the wires passing through holes 1 and 5) will be about right for a (1/4;1/2;1W) resistor or a diode.

You might prefer perfboard instead. It depends upon what you find easiest to use (which can in turn depend upon the particular project).

You can cut the boards to size with a fine toothed (~30+ tpi) hacksaw.

Originally Posted by IamIan

?? I don't see how it could possibly tell the difference ?? ... From it's point of view force is force in x direction is force in x direction ... be it Gravity ( incline ) , or vehicle ( sensor ) acceleration.

Exactly.

[Occasionally6]

Originally Posted by jeff88

Like I said, I do like the idea and it did get me to wondering if I could use an Arduino based GPS shield to get the same effect and it would still be able to send the result to a display of my choosing. I don't know if this is possible, maybe Occasionally6 can chime in on that.

Using just topographical data may be possible DIY but I don't know how to do it.

This may be useful:

https://www.sparkfun.com/tutorials/169#gpsinside

Originally Posted by niky

The Racelogic V-Box gives you altitude readings in diagnostic mode, accurate to a tenth of a meter or so, given a good signal and an external antenna.

But it's a squiggly little number on a diagnostic screen full of satellite tracks, GPS time, latitude and longitude coordinates and etcetera.

That Racelogic does it means it is possible to use a GPS signal to determine velocity and elevation in real time. The supporting documentation for the Racelogic loggers says it uses the Doppler shift in the GPS signal data. I think that's beyond DIY.

That the price tag on the Racelogic stuff is $1K+, however good the quality, might be some indication of how difficult it is to do in that way.

[niky]

Even the $400 basic V-Box has the function on its diagnostic screen. But I don't know if it's as accurate as the horizontal distance function.

[jeff88]

Just wondering how your setup is doing. Is it working properly? Have you figured out how exactly you want it setup? How does it do with just the accelerometer and no gyro? How often does it "reset" itself and how fast does that process take?

I just realized, if I have a 2 digit display, that displays 7.2 or 8.4 or whatever, I won't have a way to display a negative. For large percentage slopes, I can probably tell if I am going up or down but for smaller slopes, it will be more difficult to know what the car is doing (up or down). I wonder, since their is a decimal point after the second digit, if I can set up the second decimal as my negative.

Trying to find a non-discontinued analog gyro/accel. is proving difficult! I have to try and find a tut to help me with I2C, because it seems that is the only way to go at this point. Have you seen anything regarding how to use I2C?
This page helped: Accel/Gyro Guide
I did find these:
Analog Gyro This one is waaaay to expensive though!
Serial Interface Gyro/Accel. This one says it outputs on a serial interface. Is that SPI? Would this work as an "analog" output?
Dual Axis Gyro This one looks to be analog, but I don't know if it would work for this application. It's only the gyro, no accel.
Analog Accel. This one is cheap, +/-1.5g and has (I think) analog output. May be a good option if I can't find an integrated gyro/accel.
MMA7361 This one offers analog output and +/-1.5g.

The only way to get around I2C, would be to have 2 separate shields, but finding a gyro by itself that uses analog output is fairly difficult as well. What's so different about I2C compared to analog (at least in terms of the sketch)?

Should I get some capacitors as well? Will it be of benefit for me?

Do you know what I should look for in a gyro? I see +/- 250, 1,000, 2,000, etc., but what is needed for this application? Is it the smaller the range the better like the accelerometer?

[Occasionally6]

Originally Posted by jeff88

Just wondering how your setup is doing. Is it working properly? Have you figured out how exactly you want it setup? How does it do with just the accelerometer and no gyro? How often does it "reset" itself and how fast does that process take?

Slowly. There's no deadline so it happens when I feel like it. It's just playing around with the sketch(es) atm.

The set up hasn't changed; VSS input + analog accelerometer input. I haven't yet set up a speed sensor input. I will do that on the bench before putting it in a car. That is another mini project by itself.

Other than for a vertical displacement (for calculating PE) there is no need for a reset because the VSS is a constant connection to the real world. The reset/reference is only required for dead reckoning which always has some inherent error.

I just realized, if I have a 2 digit display, that displays 7.2 or 8.4 or whatever, I won't have a way to display a negative. For large percentage slopes, I can probably tell if I am going up or down but for smaller slopes, it will be more difficult to know what the car is doing (up or down). I wonder, since their is a decimal point after the second digit, if I can set up the second decimal as my negative.

Clever. That's a nice way to do it, with the 7-segment dp pin wired to an Arduino pin. An extra 7-segment (+ transistor and current limiting resistor for the transistor) just to display the minus sign would also work.

Trying to find a non-discontinued analog gyro/accel. is proving difficult! I have to try and find a tut to help me with I2C, because it seems that is the only way to go at this point. Have you seen anything regarding how to use I2C?

You might start here:

Arduino Playground - MPU-6050

and strip out the temp sensor from the sketch (unless you want that).

Maybe here also:

Playing with an Arduino and sensors

I did find these:
Analog Gyro

It's analog but does that have more than one output? I can only see reference to 'z' axis. I think you need at least two unless you want to do what I will have to do and estimate or ignore the effect of lateral slope.

Serial Interface Gyro/Accel. This one says it outputs on a serial interface. Is that SPI? Would this work as an "analog" output?

Definitely serial which means it can use either SPI or I2C with Arduino. It also needs a 5V FTDI Basic Breakout (or equivalent) in order to program it.

At the risk of confusing you, Arduino's come in a few different forms, some of which, unlike UNO and Mega, don't have included on the board the means to program them with the sketch. Those need the FTDI breakout (or equivalent) to get the sketch to the Arduino. You could use the FTDI breakout which is needed to program that IMU (which uses the same Atmega328 chip as the Arduino) and an alternative (maybe cheaper) form of Arduino if you have to buy the FTDI breakout anyway.

Dual Axis Gyro This one looks to be analog, but I don't know if it would work for this application. It's only the gyro, no accel.

That one looks OK. It is two axis only but I think that's all you need.

Analog Accel. This one is cheap, +/-1.5g and has (I think) analog output. May be a good option if I can't find an integrated gyro/accel.
MMA7361 This one offers analog output and +/-1.5g.

They are both the same MMA7361 IC that I am using. Unless you want to get into making your own board, soldering surface mount components, (you don't) the second one, with that already done for you, is the one you want.

The only way to get around I2C, would be to have 2 separate shields, but finding a gyro by itself that uses analog output is fairly difficult as well.

You can put two sensors on one shield but if they are two discrete sensors you'll have to match them onto a common axis in the sketch.

What's so different about I2C compared to analog (at least in terms of the sketch)?

Once you get the sensor input into the Arduino, very little. The units might be different but that's not difficult to deal with. It's just getting the sensor input into the Arduino that is a bit more complicated. That does require a more complex part of the sketch to achieve. It's Arduino so I can't see it being too difficult. I think copying and pasting the code from the playground Arduino.cc link above would do it. (Having written that, I haven't actually done it so...)

Should I get some capacitors as well? Will it be of benefit for me?

For what? I have the two on the power supply that the shield allowed for to damp any fluctuations or noise on that. I think that's probably sensible. I'm going to try some across the (analog) sensor outputs to see if that reduces the noise on them.

Like here:

Accelerometer Experiments – Part 2: LIS331AL and DE-ACCM2G (ADXL322) . Filters, amplifiers and vibration response. « Starlino Electronics

That (starlino) site (chase the link back to menu page for a lot more) has a lot of relevant information for us, particularly the mathematics that are required to shift axes. There is also a description of a simplified version of the Kalman filtering (using a constant weighting to average the gyro and accelerometer inputs to determine the position sensing input). Those pages are worth reading.

Do you know what I should look for in a gyro? I see +/- 250, 1,000, 2,000, etc., but what is needed for this application? Is it the smaller the range the better like the accelerometer?

Pretty similar as far as I can tell. Aren't they mV per unit of angular acceleration, in degrees per second, the rotational analogy to linear acceleration. The other main gyro spec. is total degrees per second. Measuring slope will be pretty undemanding in terms of that.

[jeff88]

Originally Posted by Occasionally6

Slowly. There's no deadline so it happens when I feel like it. It's just playing around with the sketch(es) atm.

The set up hasn't changed; VSS input + analog accelerometer input. I haven't yet set up a speed sensor input. I will do that on the bench before putting it in a car. That is another mini project by itself.

Other than for a vertical displacement (for calculating PE) there is no need for a reset because the VSS is a constant connection to the real world. The reset/reference is only required for dead reckoning which always has some inherent error.

Keep me posted with updates!

How do you bench test the VSS? Are you going to do something similar with the voltage divider and patch ECM cable and whatnot?

So because you are not putting a gyro into the system (yet ) you don't need to worry about the reset then, there's no drift on it right?

Originally Posted by Occasionally6

Clever. That's a nice way to do it, with the 7-segment dp pin wired to an Arduino pin. An extra 7-segment (+ transistor and current limiting resistor for the transistor) just to display the minus sign would also work.

I looked for a triple digit 7-segment display, but couldn't find one in blue (at least not on Amazon). That's why I figured I would do the decimal point thing. I figured I didn't really want to do 2 separate displays, especially just for a negative number which may or may not come on very often anyway.

Originally Posted by Occasionally6

You might start here:

Arduino Playground - MPU-6050

and strip out the temp sensor from the sketch (unless you want that).

I was looking at that one, but I knew it was I2C, so I skipped over it for now. I'll probably go with it, since I can't seem to find any analog ones. It seems to be one of the least expensive options anyway.

Originally Posted by Occasionally6

At the risk of confusing you, Arduino's come in a few different forms, some of which, unlike UNO and Mega, don't have included on the board the means to program them with the sketch. Those need the FTDI breakout (or equivalent) to get the sketch to the Arduino. You could use the FTDI breakout which is needed to program that IMU (which uses the same Atmega328 chip as the Arduino) and an alternative (maybe cheaper) form of Arduino if you have to buy the FTDI breakout anyway.

We'll skip that for now! I think I get what you're saying, but I don't think it's necessary to get into that for what I need.

Originally Posted by Occasionally6

Once you get the sensor input into the Arduino, very little. The units might be different but that's not difficult to deal with. It's just getting the sensor input into the Arduino that is a bit more complicated. That does require a more complex part of the sketch to achieve. It's Arduino so I can't see it being too difficult. I think copying and pasting the code from the playground Arduino.cc link above would do it. (Having written that, I haven't actually done it so...)

I think I will just go with an I2C device then. Once I get it, I can try the copy and paste method and if it doesn't work, then I can tweak it as necessary.

Originally Posted by Occasionally6

For what? I have the two on the power supply that the shield allowed for to damp any fluctuations or noise on that. I think that's probably sensible. I'm going to try some across the (analog) sensor outputs to see if that reduces the noise on them.

To help eliminate the noise. If you try it and it works better, then I figured I should get a couple, especially if it only costs me a few pennies each.

Originally Posted by Occasionally6

Pretty similar as far as I can tell. Aren't they mV per unit of angular acceleration, in degrees per second, the rotational analogy to linear acceleration. The other main gyro spec. is total degrees per second. Measuring slope will be pretty undemanding in terms of that.

So it doesn't matter what measurement rating it is then? Or should I look for the smallest one possible (say +/-250 like the MPU-6050 like you suggested)?

[Occasionally6]

Originally Posted by jeff88

Keep me posted with updates!

Sure. I have got some good ideas from the discourse on here.

How do you bench test the VSS? Are you going to do something similar with the voltage divider and patch ECM cable and whatnot?

What I have planned is using the tone() function in the Arduino to generate a square wave signal on a digital pin (i.e. any particular pin). That will be in response to a variable 0-~5V input (via a trim pot connected to an analog pin), using the map() function to convert 0-~5V to the appropriate frequency. I could just change the frequency of the tone explicitly in the sketch but bread boarding the 0-5V input is easy and easy to adjust.

0-100Hz will do for your car (I have yet to measure mine; no shop manual but it does use a Hall sensor). It depends upon tyre size, but that assumes 4 pulses and ~2 1/2ft travelled per wheel rev. and 100mph max. speed.

The tone() signal will switch a transistor that earths a 13.8V (or 11V for you) source. That's my Hall sensor emulation. The patch harness and voltage divider will be as previously described and feed back into another digital pin, that part being as it will be in the car.

So because you are not putting a gyro into the system (yet ) you don't need to worry about the reset then, there's no drift on it right?

That's the idea.

I think I will just go with an I2C device then. Once I get it, I can try the copy and paste method and if it doesn't work, then I can tweak it as necessary.

While there's no substitute for actually doing it, you might find it useful to download the Arduino IDE and play around with some sketches. You won't find all the possible problems but you can try to understand what is being done and at least see if the changes you are making result in a sketch that can be compiled.

To help eliminate the noise. If you try it and it works better, then I figured I should get a couple, especially if it only costs me a few pennies each.

100nF across the accelerometer board output voltages and ground didn't make any appreciable difference to the readings. (That means there was 106.8nF capacitance across the outputs from the IC because there are also 6.8nF capacitors on the outputs to ground on the board I am using.) The capacitance is combined with the resistance in the IC to block specific frequencies, probably close to the optimum, so I didn't expect too much, but it was easy to do and cost nothing. I might play with some different capacitances but I don't expect too much more from doing it.

Capacitors across the power and ground might be of more benefit, particularly if you are switching relatively high currents on and off.

There is scope to reduce noise within the sketch. Two ways I am playing with are to use a rolling average (varying the number of samples) or use a series reduction that weights more recent signals more heavily than earlier eg. (using 6 sample readings) Xc = Xc/2 + Xc-1/4 + Xc-2/8 + Xc-3/16 + Xc-4/32 + Xc-5/32 (think that is an FIR filter). The last "/32" is to get the total of the co-efficient fractions to add so as to equal one while using a finite number of samples. The co-efficients can be arbitrary instead, with heavier weighting to the latest or earlier samples. I haven't (yet?) looked at using a statistical method.

So it doesn't matter what measurement rating it is then? Or should I look for the smallest one possible (say +/-250 like the MPU-6050 like you suggested)?

You will be able to figure it out better than I can. The angle that is being measured is quite small and, neglecting road bumps, the rate of angular acceleration likewise low. Resolution is important.

It's possible that a road bump might produce a rapid angular rotation. You might have to compensate for that in the sketch eg. discard an angular acceleration above a certain rate and use the previous value, filtered or not.

[jeff88]

Looked up some DMMs, but I am still stuck on what will be of benefit (for this project and general purpose uses).

Here's some that I have found online:
Equus 3320
Equus 3300
Craftsman 34-82141
Sinometer
Elenco
Is there one in this list that sticks out to you that would work, or I am too far off with these?

Also, I have added links to the exact items I am going to get in my parts list. Can you just double check to make sure I am getting the correct items before I order them? I want to order them this week or next, but want to make sure I get the right things first.

I put a relay on the list originally, but now am wondering why I did so. Can you think of a reason at this point why I would need one?

Should I get some male to male pin headers to make soldering the wires on easier or can I just attach the wires directly to the board (I assume this might be difficult in the long run as the wires might come out with vibrations and whatnot, plus the headers would make taking the wires out easier, if need be)? Is there a special Arduino pin header or are all pin headers the same (other than # of pins)? I assume I should be looking for a pin header for less than a dollar a piece (or maybe literally just a few pennies a piece)?

How should I mount the Arduino and accel/gyro? Can I just drill some holes in the veroboard and screw them directly to the board, or should I mount it to something else, like a piece of aluminum or wood with some bolts and nuts and maybe some rubber washers (for vibration control)?

[Occasionally6]

Originally Posted by jeff88

Looked up some DMMs, but I am still stuck on what will be of benefit (for this project and general purpose uses).

I don't think you are too far off, no. I wouldn't like to pick one out though. I think that should be your decision (sorry).

Also, I have added links to the exact items I am going to get in my parts list. Can you just double check to make sure I am getting the correct items before I order them? I want to order them this week or next, but want to make sure I get the right things first.

Current limiting resistors for the display and for the transistors? You'll need to put together a schematic design and work out what they should be first.

Do you still need the Mega when using I2C, given that I2C will only need two digital pins rather than 6 analog pins?

I put a relay on the list originally, but now am wondering why I did so. Can you think of a reason at this point why I would need one?

Not really. Maybe there's some benefit to keeping the unit isolated from other circuits in the car to avoid noise. The current it draws (it needs to be under 200mA total to protect the Arduino) won't be enough to require a dedicated circuit and it can be connected into an ignition switched supply. I'd (will) try it without one first.

I can't recall the last time I bought a relay anyway. They're usually free from the junkyard, especially if purchasing something else.

Should I get some male to male pin headers to make soldering the wires on easier or can I just attach the wires directly to the board (I assume this might be difficult in the long run as the wires might come out with vibrations and whatnot, plus the headers would make taking the wires out easier, if need be)? Is there a special Arduino pin header or are all pin headers the same (other than # of pins)? I assume I should be looking for a pin header for less than a dollar a piece (or maybe literally just a few pennies a piece)?

I used the pin headers to make the connection between the shield and the Arduino. The pins are soldered to the shield and a push fit into the female sockets on the Arduino. There are a few tutorials around on doing that. Adafruit has (at least) one. That means the shield is easy to separate from the Arduino and there's no permanent alteration to the Arduino.

They are not locked in any way but are a pretty solid friction fit (there are 28 of the pins and sockets).

The header pins are a standard 0.1" spacing.

I have the wires soldered directly to the shield, in the through holes.

If you want to be able to separate the wires from the board, you could use PCB mount friction locking header connectors.

Like this:

5 Position 0.1" Straight Friction Locking Header: Amazon.com: Industrial & Scientific

plus the corresponding female part. There are 90 degree versions of the male connectors if that packages better.

One part is soldered to the board, the socket terminals are crimped or soldered to each wire, pushed into the second part and the two parts snap together.

What you use is up to you.

How should I mount the Arduino and accel/gyro? Can I just drill some holes in the veroboard and screw them directly to the board, or should I mount it to something else, like a piece of aluminum or wood with some bolts and nuts and maybe some rubber washers (for vibration control)?

As you may recall (or can check in the images) I have the accelerometer board mounted solidly on the shield, held in place solely by the soldered wires, so I only have to figure out a single mount for the Arduino plus shield, and one for the display. It will all end up in what is currently a storage slot in the dash.

Doing it again, I would not solder the connecting wires with the accelerometer board resting on the shield. That makes the accelerometer board difficult to remove (should that be necessary) by soldering the solder pads on the two boards together. A better way is to space it off the board with a thin, flat insulator eg. a scrap of bench top laminate.

While I have some idea, I haven't fully thought out how to mount mine yet. Worst case, there's always epoxy adhesive .

I am not anticipating vibration to be a problem and something I think I can deal with in the sketch if it is.

It probably won't hurt to rubber mount the parts but most automotive electronics are solidly mounted.

The accelerometer board at least already has holes in it for the purpose of mounting it to something. You can certainly drill holes in Veroboard.