The olrowdy smaller OBDII case

Last update:   5/21/2015  Return to Insight home page
How to make the mount for the OBDII gage

View of completed case
My homebuilt case for the OBDIIC&C

The front of the case can't be made any smaller than this with the present sized PCBs.  Neater yes, smaller no.

Introduction to OBDII

Our Insights have an "On Board Diagnostic" (OBDII) system which has the usual OBDII information available at the diagnostic connector.

There are also more than 125 codes (the number varies depending upon the country and what transmission the car has) applicable to the Insight that can be read out with a specialized OBDII gage.  Honda dealers have a HDS gage they use to analyze problems etc on their cars.  Unfortunately HDS gages aren't cheap or made to be dashboard mounted.  A normal OBDII gage can not read all the specialized codes that the Insight has.

One of the UK posters, retepsnikrep, has deciphered the OBDII data stream from several Honda cars and has designed and sells an OBDII that can read the Insight data.

A ready made Insight capable OBDIIc&c gage, a gage kit or parts can be bought from the designer at this link.

I have no financial interest in his company.  I am just trying to spread the word.


The original case for the OBDIIC&C gage assembled in the USA had a rather large case.  This made it difficult to find a good mounting place for the gage without blocking the forward view through the windshield.  Some people mounted the gage near the cup holders but I thought that it was too hard to read the gage since your eyes completely left the road and could create a driving hazard.

I had it in mind to reduce the case size by mounting the LCD display panel remotely from the mother board.  I bought the PCB and the 5-way switch to build the unit DIY style.  After receiving the PCB and the display I realized that the larger mother PCB set the size of the unit because of the 5-way switch and two LEDs mounted on it.  Those parts can't be easily mounted on the display PCB  and if remotely mounted the front of the case wouldn't be much smaller than the original mother board to be able to accommodate the switches and LEDs.

After pondering this turn of events a bit I found a 5"L x 2.5"W x 1.625"D plastic box  in my extensive junk box and used it for my case.  This article explains how I made a minimum sized case that can still contain the PCBs etc.  The box number is 273-233 and at first I was not able to find who made it decades ago.

Recently I found a Radio shack box that is 5"L x 2.5"W x 2"D, p/n 270-1803, that may be usable.  The depth is 3/8" greater than my box but that can be trimmed down to size. Luckily the depth is not a critical measurement.  The box is made of ABS which is rated for -4 to 176 F service.  There should be no problem with the sun warping the case.  Since the p/n are similar to my box and appears to also be ABS I think the new RS box is the modern equivalent to what I used.

Another case that may also work is the Bud CU-1943.  This case is a little longer than needed but may require less machining to fit the boards inside. This case is also made of ABS and is rated for -40 C to +40C.  At the present time you can buy this case for $3.03 plus S/H from  Allied Electronics.

Recently one of the posters on the  has been experimenting making a case with a 3-D printer.  The first test looks very good.  I will post information here if he develops cases for sale or posts the printer instruction file as a DIY.

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Will the PC boards fit in the case you'd like to use?

I like to think out of the box.  You get more interesting designs that way.  Here is how I figuratively turned the case inside out.

The out of the box thing I did was to mount the gage so the display face will be positioned through the bottom of the box.  The rest of the design follows from that simple change.

The first chore if you want to try mounting your OBDII in a small case is obviously checking if the larger PCB will physically fit into the very bottom of the case ignoring for the moment the box internal mounting posts etc.  While the larger PCB won't be at the bottom of the box, the mounting spacers projecting from the main PCB will have to fit at the bottom because the larger PCB determines where the spacers are located when they touch the bottom of the box.  

All economically made molded parts (plastic boxes included) have a slight taper (typically just a degree or two) from the open end to the closed end.  This is done so the part can be removed from the molding machine.  So even if your PCB will fit within the open end of the unmodified box it might not fit at the bottom.  And you can't just drop the board to the bottom to check with the normal cover mounting posts etc in the way.

The easy way to check if the boards will fit is to place the box open end up on a table, hold the larger PCB so it is vertical and place it into the box to check the width and then the length.  If it fits with a little play in each direction then continue reading how to make a smaller case.  If the PCB doesn't fit into the bottom  ....... you need a larger box.

Now that we know the PCBs will fit in the bottom of the case to be, we have to connect the PCBs with the proper length spacers so they can be mounted at the bottom of the case by screws at each corner.  At the same time since the normal case cover mounting posts are going to be removed the back cover has to mount onto the PC board rear spacers.  The length of all the spacers depends upon several things that will probably be different from my set up.  This will become clearer in the first picture below.

Normally the two PC boards are mounted to each other with 1/8" thick spacers to move the display PCB away from the mother board.  This is done so the soldered parts etc don't short out between the boards.   The way it was originally was to electrically connect the two PC boards with a 1/8" high 16 pin connector.  I wanted to be able to easily separate the two PC boards later so I used a male-female set of 16 pin connectors.  Unfortunately the only set I had required a 3/8" space between the PC boards.  Since I was more concerned with the width-length of the case than the depth I didn't fret over the extra 1/4" of depth of my finished case since I am able to use it to hide the way I mount the gage on my dashboard.  The designer of the gage now uses a similar approach to mounting the display onto the mother PCB.

See this article for more information  how make the mount for the OBDII gage.

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To see an enlarged view of most pictures, click on the picture or right click and select "View Image".

    Here are the assembled PC boards with the spacers attached
PCBs stacked

This picture shows the two PC boards and the back cover assembled together.  In affect what you see here is the minimum depth my case can be.

Also note the 3/8" high male/female 16 pin connector connecting the LCD display PCB to the mother board.  I left the pins long as test points.

The pair of two spacers on the left side of the PCBs are internally threaded #4-40 and are held together with a short #4-40 threaded rod made from cut off #4-40 screws.

The middle spacers on the right side have a #4 clearance hole and the other two spacers are threaded #4-40.  The three spacers and the PC boards are held together with #4-40 threaded rods.  The length of the 4 top spacers in this view are determined by how thick your case is.  The bottom spacer length is determined by how much clearance you need above the parts.

PCBs & case

This picture shows the other side of the PC boards etc with the now "front" of the case which originally was the bottom of the box.

When you enlarge the picture you might be able to make out the small metal plug cover in the left side of the case that covers the Picaxe connector mounted on the mother board.  Junk box to the rescue again.

Note that the LEDs are mounted on standard X plastic spacers used for this purpose.  The LED leads fit into opposite sides of the X.  I made the 28 pin PIC socket from two modified 14 pin IC sockets.

Also notice that two of the mounting screws are shorter than the other two. This is necessary because the spacers at each end of the mother board are different lengths and the threaded rods threaded into those spacers use up more of the available thread on the left side.

Vew of motor running

This is of course the front of my OBD II case. Since the PCBs fill up the entire interior width and height of the case there is no way to make the case any smaller.

The LEDs really aren't turned on in this picture.  They are reflecting the camera flash.  The LCD fits squarely in the hole and the display is not crooked in the case.

Note my elaborate 5-way switch knob.  It is a nylon bolt held onto the square post of the flush mounted switch with a piece of heat shrink tubing.  I machined the bolt down a little as it passes through the case so the case hole isn't any larger than the head diameter of the bolt.  I was having trouble when pushing the 5-way switch and finally installed a push button switch on the bottom of the case wired in parallel with the original 5-way switch.

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Back of case

And here is the back cover made from the original cover of the box. The cover had to be trimmed a little to fit deeper into the box. When you look at the enlarged picture you will see the original mounting holes that aligned with the now removed cover posts.  But since this is the back of the case they won't be visible.

I used two junk box computer connectors for the ICSP and OBDII connectors.  Notice that they are two different shapes so the cables can't be plunged in backwards or interchanged.

Since this picture was made I installed the mounting brackets and punched a small hole in the cover in alignment with the hole in the beeper. This allows the sound to get directly out of the case.

And now the actual modifications to create the smaller case and the OBD connector

The newer RS case 270-1803 has guides to mount PCBs vertically in the box.  You will have to carefully measure the case to see if the OBDII boards and display will fit into the case if the guides and posts are machined away.

The display board will be positioned at the very bottom of the case.  My mother board is mounted ~3/4" above the bottom of the case.  The SIP connector I used to mount the display onto the mother board increased the height somewhat over soldering the LCD in place.  So measure carefully several times and machine one time.

If you use thin tube spacers it may still be possible to mount the OBDII gage in the 1803 case with screws from the front (original bottom) of the case.

case with posts

This is the case before I removed the internal mounting posts etc.  There is a part number (270-233) cast in the case but I'm not sure who the manufacturer was. I believe the p/n is a discontinued Radio Shack number.

case no posts

This is the same case with the posts and other projections removed using an end mill in my drill press.  The bottom surface has to be  flat so the spacers will bottom squarely.

cutting hole for display

This picture was made while I was cutting out the hole for the display to be mounted. I first drilled holes within the outline of where the LCD display frame will project thorough the case.  I then used a hand nibbler to remove the center of the rectangular hole to fit the actual display.  The final fitting was done with a hand file.

The four mounting screw holes had to be carefully measured, drilled and then "adjusted" in placement with a die makers file set.

Modifying the box to become a case took a lot of measuring and filing to accomplish.

OBDII connector

I wanted my gage to be turned completely off when the ignition key was removed.  The gage normally draws it's power from the always on 12V battery system pin of the OBDII socket.

The small power socket will be mounted in the side of the OBDII connector. A single wire is connected to the under dash fuse box to a fuse used in Canada for the DRL 12V switched power circuit.  That fuse is installed but isn't used on my USA car.  There are other empty fuse sockets that might be usable.  I modified a burned out fuse by baring a little bit of one spade lug on the fuse and soldering the power wire to it. Insert the fuse so the wire is closer to the floor of the car.

3/4 view OBD

A view of the mounted connector. Make sure that you mount the power socket so it is accessible  when the OBDII connector is plugged into the car.

The cable to the gage will come out what is the bottom of this connector picture when it is plugged into the OBDII socket.  This is shown in the picture below.  I used a shielded 4 wire lead cable.

The connector is shown upside down to how it is plugged into the car.

view of mounted power socket

Here is how the added 12 volt power socket is positioned inside the OBDII connector.   The new power socket was hand fitted and filed to fit. It is held in place by the top and bottom covers of the OBD connector.

The brass solder lug of the power socket was rotated upwards after this picture was taken so it cleared pin 16 of the OBD connector.  Pin 16 is the OBDII all time on 12V power pin and is not used with this connector modification.

wired OBD

And here is the wired OBDII connector.  The orange wire is the 12V power to the OBDII gage connected to the center pin of the power socket.  There is no ground wire connected to the power socket. The OBDII gage ground wire is connected to pin 5 of the OBDII connector.

Note that  pin 16 of the OBD connector near the added power socket which normally supplies the 12V has a short piece of heat shrink tubing covering it so it can't make contact to the new power socket.

You could also cut into the OBD cable and splice the switched 12 volts into the power cable while leaving the red wire not connected in the OBDII connector.  But I wanted the cars wiring to remain stock in case a normal Honda HDS OBDII gage was used by a dealer.

OBD2 mounted

I have come up with a way of mounting the gage to the left side A/C outlet duct without any changes to the dash.  This picture was made while I was test fitting it to the dashboard and the gage is not quite in its final position.

It is easy to install or remove the gage in just a few seconds once the secret is revealed.  :-)   I use computer connections for the PCB headers and the OBDII cable exits the case in the upper left hand corner which is just above the sloping dashboard in that area.  The cable heads directly towards the windshield at first, then down into an opening on the left side of the dash at the base of the windshield pillar.

The gage does not block any of the switches or controls near it.  And it is easily removed for updates or testing other Insights.

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How make the mount for the OBDII gage.

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