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Remote "Back Window" MPG Display?

13672 Views 75 Replies 29 Participants Last post by  Insightful Trekker
Has anyone been able to extract segment driver information from the dash MPG display and been able to fabricate a nice bright large display for MPG so drivers behind me can see how I'm doing? Are their any remote MPG display kits being marketed? I think that alone would be responsible for for increase in Insight interest as much as anything else. Fred in Michigan.
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I have been thinking about this since I got my Insight in 2001. Reverse engineering the serial communication protocal could be very time consuming, and tapping into the LCD display which is probably multiplexed would be messy. I figure that The simplest way is to have a bright rear color video display, and a small color video camera that is focused on the part of the main LCD that you want to display. It would probably not be daylight readable, but would be easy to see at night. :D
Hi Yves
As you may remember, I had made a reader for the bar graph that captured the average intensity of all the bars, and converted it to an analog voltage. This voltage was to be converted to a repeater bargraph in the rear window.
It could be made to work well(+- 1-2 bars) as long as the ambient light was dim, but if the sun got onto the display it would cause the voltage to change wildly, so I gave up on that approach, and figured that someday I would have the time to reverse engineer the "meter serial" communication and keep it digital. I also had a heads up lean burn led that used a single fiber optic with detector to read one LCD bar at about 65MPG.
It had the same problems with ambient light.
If one is willing to completely cover the bargraph so ambient light cannot get into the detection circuits, you could put the photo detectors right against the LCD bargraph. Once the repeater circuit was working, an additional bargraph could be mounted over the opaque cover so the instant MPG bargraph (repeater) would still show the MPG on the dash, and also in the rear window. It may be worth a try?
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While a rear display of MPG that is hand entered would be fairley easy to do, it will not have the real time effect that I was hoping for. I mounted a color ccd video camera on a simple metal bracket that is pressed down into the crack between the steering column cover and the dashboard. The camera is kind of big, and blocks my view of the mpg bargraph, but is a good proof of concept. I made a close up lens so the camera can be focused on just the MPG and bargraph. The bargraph is visable with 0 to 75 MPG. The display is a bright 5 inch LCD video monitor. The display is clear and quite readable once it begins to get dark.
I have ordered a tiny 1.4X1.4 inch color camera that should be able to be mounted out of the way so the instrument panel will not be occluded.
I will post some photos once I get it finished.
The full bargaph can be displayed but I wanted to have the MPG diaplay as large as possible. Moving the camera back a little includes more of the bargraph.
The camera has a pan and tilt mount so anything part of the display can be repeated in the rear display.
I have not found a reasonably priced transflective LCD video display. That type would show an image even in the day time.
I got the color video cameras today. I got the 1.4" square one that I had refered to, and an even smaller 5/8" square one. Both have adjustable focus lenses, and can focus to within a fraction of an inch of the lens. I like the 5/8" square one, since it is so small that it can sit slightly to the left of the MPG display, and not block anything, while capturing the full digital MPG display, and most of the MPG bargraph.The resolution is pretty good, and if the image does not include a lot of dark background, it is able to adjust the exposure to give a nice capture of the bargraph and digital display.
Both cameras run on 9-12VDC, so I needed to put an LM7812 linear voltage regulator in the power line, since the unregulated 14 + volts out of the lighter jack would damage the cameras.
Now I need to come up with a mounting system that will hold the tiny camera where I want it for the best capture.
I got the amazing little 5/8 color camera from:
for only $49.95, in case any one else wants to try this.
I will mount my LCD display into a recessed custom mounting box in the bottom of my Insight's rear deck window, so it may be daylight viewable, and will post some photos when it is done.
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Photos of the display with MPG data, and the camera mount in place.
Click rear MPG display on the main page near the phptp of my insight.
Simple piece of # 12 electrical wire was all it took to hold the camera.
The camera could use a little more contrast, so I will make or buy a video preamp so the video level can be controlled better.
The camera has a good depth of field because of the "pinhole" lens, so a perspective display can show more of the bargraph fading up to 100MPG
Lots of possibilities as to what is included in thye display.
Will update the photos and notify here as I continue to refine the display.

Mike :lol: :lol: :lol: :lol:
The battery monitor was the pogo pin jack on tap into the battery connector so voltages could be read to a data acquisition system. Armin has one that he measures the battery voltage of each subpack with. He also tapped into the current sensor an is able to read true amps in and out of the pack.
I still have one or 2 of the shells without pins.

I just got back from a 50 mile night trip where I tried out the display and camera .
I found a better angle to take the video from that lets you clearly read the whole display all the way to the 150 mph bar. I will put up a picture tomorrow. The monitor that I have, which is a pretty bright 6.8" TFT that I bought on line from a surplus place. It is quite readable from about the same distance as you can read the numberplate of a car at night. The TFT has a rather narrow field of view top to bottom, so the display will need to be tuned for the best passing car angle, but once set it dosen't drift.
I looked at the camera signal with a scope, and found that the full insight display briteness gives the best contrast, but shifts all of the signals up to the clip point. I cut an RCA cable and put a 200 ohm pot as an attenuator. That shifted the voltage into a better range and improves contrast.
I wish I had a narrow bandpass optical filter that would improve the contrast of the lit segments to the background.
It is uasble as is.
The video display can be flipped horizontally and vertically, so for the hell of it, I put the display on the top of the dash and reflected it off of the windshield. I flliped the reversal switches and adjusted the TFT and low and behold my full MPG display is also displayed as a heads up color real time display that has big enough numbers and bars as to not be distracting to read even with the dual reflections.
Will take photo of the heads up display in actual driving on another night trip and put it in the photo page.

I have about 5 of the monitors (was going to be part of my future video intercom), so I will make enclosures for both.
If the tinted rear deck window blocks too much light, I will make a waterproof external display that sits right above the H onda emblem. If guys like Rick Reese and the other high milage guys had these displays, people would be reminded or how good hybrid cars are every time they got close enough. It would also allow someone to teach other hybrid drivers how to drive. The student would follow the expert, and try to match the experts MPG under the same exact conditions. Rick Reese sign me up to follow you for a few miles once you get instrumented.
The first reaction I had to having the rear display, was to reset my segment display, and start driving efficiently, because now I could imagine that the guy behind me could see how I was doing . The thing will surely need an on off switch for those days when you are in a hurry.

:lol: :lol:
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Photos of the optimized MPG rear display, and the heads up display are now available @:
under Rear mpg display.

I did not have the display in the rear deck, so no one could see it. I had it mounted to my instrument console over the shift lever where I could see it at about chest high.
I will build an enclosure for the rear display that either is waterproof and mounts outside to give maximum viewability, or inside the tinted window which will keep it dry but because of the tint, further reduce the viewability.
I am a littlle busy installing a solar collector system for my home, but hope to have it made and running buy early next week.
I did an on line search to find out how much auto LCD video monitors cost.
The range of prices that I found was $130 to 299, depending on size and features. Add $50 for the camera, and you have a rear MPG display.
I finally had some time today, and I finished the rear MPG display. It will get some finishing, maybe an anti reflective protective glass, maybe a video amp to allow increasing contrast, and a simpler to remove mount in the future, but for now it is up and running. I put up anl Insight Modification page on my web site, where photos of the display can be viewed. I will be going out to the movies tomorrow evening, where a few trips around the parking lot when the movie gets out should see if the display has the desired effect.

See the worlds first rear MPG display @: ... isplay.htm :lol:
Hi Yves
I had purchaced 8 of the LCD video monitors at the MIT electronics swap meet several years ago from a surplus dealer for about $75 ea. and the tiny color camera was $50. I did a search on line, and found lots of LCD displays in the $135 to $299 range, most were already in a case, where as the ones I have are just the modules. The best type would be the transflective type since they are viewable in direct sunlight. If you got a smaller 5" size, you may be able to mount it inside the rear window, and focus on just the digital MPG display and get the same size image.
Have some fun, and help let the world know that hybrids really do get 60+ MPG.
While the photodiode gate concept seems simple in principal, it is quite difficult in practice. The contrast ratio of the display segments between on and off is not as large as one would like to get reliable switching even if the photo detector was placed right on the display. When I first got the Insight, I played around with trying to get a single led to light up when the MPG bargraph went into the lean burn zone. I mounted a photo detector right on the display, I also tried a plastic fiber optic to bring the light into a dark box where the photo detector as was coupled to it. When the sun got onto the display it caused the led to light even when the segment was not on. Threshold adjustment was needed between day and night even without the sun on the display. A single background light compensation photodetector was able to help, but unless it was placed right in the area of the bargraph segment that I was looking at, it could compensate incorrectly.
Detecting the 2 segments of the 100's digit and the 7 segments on the 10's, units, decimal point, and 1/10 digits would be 24 detectors that would need threshold adjustment and compensation inputs. The only way I can see to get the detectors to see the display without being in the way of your view would be to use a lens to image the display onto the detector circuit in your flat black box. The position of the box/detector to the display would be very critical, and difficult to adjust..
You would be basically making a custom 24 pixel camera. The $50 video camera already has AGC, light compensation, 640X480 pixel detector and video driver built in, alignment is easy since you can see on the video display what the camera sees.

Geoff Shepherd suggested that the video image could be sent to a computer where OCD software would decode the numbers, and then one could output 7 segment data through an I/O card. While that could work, it is even more complex .
I guess I don't see what is so hard about buying a camera and monitor, pluging it in and adjusting the lens for the view that you like?
The video solution is pretty much two off the shelf components, and a little work to mount the camera and LCD display.
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Thanks guys
I took a ride last night after making some of the changes that were suggested. The major one was to focus on getting the best display of the digital information . What that display looks like is shown @ ... isplay.htm

It was raining last night so I took some towels and propped up the rear display in the little window on the passenger side.(I was in a hurry, so I was the passer.)
That way it is only visible when the passing car is only 5-10 feet away when iit is easily readable, and he is likely to look,
That also allows the display to be inside out of the weather.
As Calpod suggest, a single display just behind the seat backs would be readable from either side, or could be mounted on a base that you could toggle between passer or passee positions. while driving. It could also have a parking lot position looking up out of the window for people walking.
Hi Yves
I moved the camera in closer as you suggested, to see if their were any issues.
The camera is easily focusable to only include the numbers, but to get all of the potential digits including the 1 for over 100MPG, the numbers for the bargraph can still be seen. A simple black tape mask can solve that problem. The digits were about 1.75 inches tall on my 6.8" LCD. Eliminate the 100's digit, and the digits can be over 2" tall.
One problem that cropped up was that the #12 wire that holds the camera, was not stiff enough to hold the camera perfectly still when navigating bumpy roads. The shake that was not a factor at lower magnifications became quite noticable at the higher magnification. The camera was close enough to the display, to be slightly in the field of view, whereas it was not blocking anything important when it was in the partial bargraph view. Both of the issues could be easily fixed with a little playing around with the mounting wire, and the angle of the camera.
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Looks real nice. Most of the 7 segment displays that I have ran into are not designed to connect directly to the power supply, and need to have current limiting resistors for the segments. This may be why you are loosing digits. The specifications for the displays should tell you how many volts and MA each segment can use, and an appropriate series resistor should be in each segments circuit.
You may want to look into getting an LED digital volt meter instead of the 7 segment displays, so that you can just dial in a voltage with a pot to make the display read what you want?
Chips are also available that will drive your 7 segment displays while converting a decimal number to the 7 segment control signals. It can be done with diodes as well. If you would like some help with the circuits, let me know off list.
I have built a video distribution amplifier with gain control for my video based MPG display, It has the ability to drive 4 video monitors from the single camera.It also lets me turn the 4 outputs on or off individually.The gain control will let me improve the display contrast.All that is left to do is for me to build two LCD monitor enclosures that fit into the two small triangular side windows. I hope to get to it this week.
Have fun.
Mike :lol:
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May want to hold off a little, since MIMA is letting me get MPG'S to brag about again, I will look into tapping into the meter serial communication between the ECM and the guage assembly and try to capture the MPG data. I already made the taps. If successful, the MPG data could be easily converted to a large LED 7 segment display and be able to automatically update with the in dash display.
Need to finish MIMA first. I will have my car rear MPG video set up at the Tour de sol.
Glad to see there is still interest in the rear MPG display. I was at the Hybrid meet in Natick MA.This Sat. One of the Prius Guys had a licence plate frame with a 1" tall X 3" wide display that he post his LMPG on. It is not auto updating, but is better then nothing.
Yes as I get to the home stretch, MIMA is traking all my time+.
Hope to be ready to start taking orders this week.
That,s how the display device that the Prius guy had worked, he had a small pendant that could raise or lower the set number from ther drivers seat.
I did not look it over that well, so I can't tell you much more, like how he knew what the display was reading.
Pretty simple to duplicate, but I want to make a unit that displays what the MPG display is reading.
My video system worked pretty well, but lacked high brightness, and was pretty pricy.
It also make me feel that I had to drive efficiently cause everyone was watching, and since this was pre MIMA, I was not too proud of my 60.2 MPG LMPG. :wink:
The display area on the unit I saw was smaller, and the remote programmer was the size of our key fob, but the JC whitney unit looks like a deal compared to the other units.
I believe some states have laws about any extra lights on a car for whatever purpose.
Been thinking about this a little more, and may have a way to get the MPG info into MIMA without the problems associated with decoding the meter serial com, which would still be the best way to read MPG.
Back in 2001, I did some experiments with reading the MPG bargraph with a single optical detector, that looked at the whole bargraph, and measured the change in light between no bars and full bars, in a linear fashion. Yves was also involved. The detector was in an opaque enclosure that only allowed the bargraph light to get to the detector. The problems were related to the bargraph brightness changing with the LCD brightness changes at the different settings, and with an analog system It was too difficult to keep calibrated. It also covered the bargraph so you could not see your MPG, so was not a good solution.
The optical detector in the MIMA display is converted to a 10 bit number, and since it is a computer, a program could be written to scale the data under the different display lighting conditions. The MPG display would still need to be covered to eliminate stray light, but the battery ammeter could do double duty as an MPG display. Once the MPG info is captured, a MPG based AutoMIMA control system could be programmed. A serial link to a large bright three digit MPG display in the rear hatch window, and we would have the rear MPG display, and a MPG based AutoMIMA control system. :wink:
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