The Stovebolt Site Forums The Shop Area Interiors First version of GPS speedometer for the AD truck

Pardon the glare, but here is my first GPS speedometer effort designed (as much as possible) to go with the AD truck design. With this one I had to make a new case for it (I used sheet brass and copied the original). The oddball multi-colored led lights built into this unit were disabled. I think for any future work I'd do some electronic surgery and relocate some components, shrink the thickness of the thing and try to fit it into the stock case. Either that or I may build a garolite or fiberglass case. At any rate, it works, seems accurate, is smooth and quiet, has a permanent overall odometer and a re-settable trip odometer with 4 trip choices. Hookup is not difficult. One power wire, ground back to the mounting screw, power wire to the high beam dot (an led so it won't need replacing) one wire each for left/right turn signal dots (I took the liberty of adding these...since it wasn't to be 100% original, I opted for convenience--also leds) and two wires/plug in connectors for the re-set switch which attached to the nut/bolt holding the ignition switch and hides below the dashboard. The satellite sensor will just sit unseen underneath the dashboard.

These GPS units are copies of the old Speedhut GPS 3 3/8" speedometer (no longer made) which has the proper sweep and limits max speed to 80 mph (sorry...no 90 mph models have been made). The difference between this and the Speedhut version is the Chinese took great liberty with case depth and used some tall capacitors (which may have been for a reason...or they could have simply been cheaper). There are also 120 mph versions of these available and I think they could be adapted to many different circular styles of speedometer. I haven't found one with a 90 degree sweep yet (for those horizontal type speedometer units), but a person could adapt a 0 to 200 mph unit to read 0 to 105mph with a 90 degree sweep.

This is what it looked like before I tore it up and re-imagined it: https://tinyurl.com/23nk3bzh

Looks great, Jon

Jon,

X2 on the looks.

You said you disabled the multi-colored lights. Is there still a regular back-light for night driving?

Thanks

What's the rectangle in the center?

Assuming that’s the digital odometer display

Nice job Jon! Is the needle and center section from an original speedo?

Hi folks...the needle is original and I had to adapt it to fit on the metric sized shaft of the speedometer unit. The center section of the dial is actually not original but as close to the original look as possible. It is really just a face plate I created and had printed by Kinko's/Fed Ex on color laser paper. The original center spot was cut out for the original odometer. The decal should be at the top of this section in a "sticky" along with gauge decals I provided a couple of years ago. Then I cut the bottom ridge off of a soda pop can and trimmed it to make the trim ring, polished that a bit with MAAS polish, split it, carefully pushed it over a shot glass until I got the diameter I wanted and glued it in place with some clear silicone. Yes, the little window is for the digital odometer/trip odometer. I looked far and wide for a digital GPS speedometer with a mechanical odometer, however I couldn't find one. Well, there is one, but it came in a mid 90s S10 truck and wasn't a GPS unit. I had hoped to create a more exact copy of the original speedometer with GPS technology, but apparently today's designers consider wheel-based mechanical mileage counters about as useless as floppy disks. As for illumination, I copied the original speedometer case using the 2 snap-in bulbs on either side of the speedo unit, so it looks original at night. As for the little odometer rectangle, in the daytime the numbers show black against a grayish background. At night the light from the 2 light bulbs transmit through a clear plastic disk on which the aluminum face plate I made is attached. That causes the little rectangle to light up also so you can see everything there easily. I thought about making this a project with step-by-step accounting of all I did but I didn't because (a) I'm sort of tired of doing that. I've done lots of those projects here and none of them have become tech-tips. That means they get buried and then people can't find them. Just like the speedometer work I did in the past, intermittent wipers, the carburetor work, rebuild your seat sliders, repair your headlight switch, install window rubber, etc. All that stuff vanishes and is left for people to search for. And (b) this wasn't easy. I had to create a new speedometer case unit and I had to modify the one from China quite a bit. I have decided to buy another Chinese GPS speedometer and see about creating a unit which could be simply installed into the original speedometer case, however. If you have more questions, please let me know.

Jon,

Thanks for the response about the back lighting.

Can't speak for others, but I definitely enjoy reading your posts/projects/tips (yes I have read them all and often go back and reread as I enjoy the technical info). The super deep level of thought and detailed explanations are greatly appreciated.

Please don't stop!

Thanks again!

I'm confused. Is the speedo needle driven by a cable from the transmission or is it driven by a gps signal?

Dan, thank you very much for the compliment!

The speedo needle is driven by the gps signal (through some very neat circuitry and a stepper motor). When you turn on the ignition, it will sweep quickly to 80mph and then swing back to 0 where it settles and then the odometer will activate. If a gps signal isn't seen yet, it will flash the odometer section until it does. This might take a few seconds and occasionally you need to move the vehicle so the circuit can sense something happening and move to the next stage.

This project goes back a while. I did a version of this previously (maybe 2 and a half years ago) and used a pulse output speedometer made by Speedhut. But since then some folks told me they didn't like that, weren't interested in it and appealed to me to make a gps unit. Speedhut no longer makes a 3 and 3/8" gps 0 to 80 speedometer, so I had to look elsewhere. Parts from China are less expensive, but they take a while to get here (the speedometer unit took almost 3 months). In the process I learned almost all the gps speedometers sold by others originated in China, were decorated to suit the people marketing the unit (ie they could have been 0 to 35mph, 0 to 60mph, 0 to 80mph...all the way up to 0 to 200mph, different colors, logos, and there could have been all manner of led schemes, gauges scabbed on, etc). Some are made for boats, some for motorcycles, some for home-made airplanes, etc. And in my original project I created a frankenspeedometer...an electronic S-10 speedometer coupled with a vacuum gauge and a tach. You can see it in the decal sticky at the top of this page. It works, but honestly it is too distracting to be practical so I shelved it.

Below you can see the pulse output speedometer (in the OEM case), the frankenspeedometer (which had to be put into a fiberglass case) and some images of the first brass reproduction case I made for the GPS unit.

Out of the park home run Jon!! We use nothing but gps units on all the rods we build which does away with any tire size or gear ratio issues but the factory replacement is obvious. You may start giving Dakota Digital competition. Outstanding.

Thanks Evan! Is there any pattern to the ones you use? More of one make/model?

Jon,

You sir have inspired me to try something like this for myself. Nice work!

David

Thanks David,
That's encouraging. After I get the next one started, I'll post some of what I'm doing...hopefully as a guide or at least a trail of crumbs that might lead folks around some of the swampy spots.

I am adding this to my list of projects. My speedometer has not worked since owning my truck. The square receiver hole in the gear in the transmission is stripped out and does not spin the cable anymore. Good luck finding a replacement. I haven't tried but from what I have read various teeth counts and such. Made my hear hurt. GPS sounds like the perfect solution. I often drive with my phone laying on the seat with a GPS speedometer app turned on.

Thanks Jon for all of your hard work. I know what you mean, documenting all of the steps in a project, submitting it for a “Tech Tip”, only to find that section of this Forum seems to be a dead end. I submitted one over a year and a half and a half ago “Aligning the front end of an AD truck”, and have two more ready for submission, “ 1/2 Ton Axle Repair” and one you helped me out on, “ Testing a Gas Gauge on a Stovebolt”. I even offered to help do whatever they needed to get the “Tech Tips” section back up and running.

I hope this section gets fixed, as it is, and has been, very helpful to allot of us just getting into the hobby.

Keep up the great work Jon, as there is many of us ‘bolters following your every post!

Thanks a lot, folks. I will be posting information on this as soon as I can...probably more information than I originally thought. I didn't expect as much interest as there has been...although I suppose I should have. You can always catch me at jon_goodman@yahoo.com by the way. There are some notable challenges to converting this into a unit that could be installed in the original speedometer case, but I'm of the opinion it can be done and that will be my goal.

Phil, I've made the same offer and I've also offered to clean up the old tech tips. There are dead links, image files that are corrupted or don't connect any longer (photobucket for example plus some other extinct photo hosting services) and some of the info in the older tips is not correct. It may have been at one point but things have changed.

But back to the GPS speedometer, I do have some images I can share with you today...a peek at what I'll be soon doing to this unit. So what the hey. Let's start.

In the first image below, you'll see the original AD speedometer case. Our goal (like nearly every other project I've done around here) is to leave that as unmolested as possible. And you can see the style of it and the GPS unit are not at this point compatible. In the second image, you can see I'm using the tip of an X-Acto knife to remove two little blue plugs that cover small phillips head screws. Plugs shown in the next image. In the fourth and fifth images you can see what I have to do to remove the trim ring. Basically stick a screwdriver under the thing and gently lift up on it all the way around by twisting the screwdriver blade underneath. I had to go around it a couple of times. And then at a point I can work the blade under it and then gently work it off. Be careful. The lens in this is glass...curved slightly outward (which I found interesting). Next we'll look inside...

Back again with another 5 image allowance. Loosening the 2 phillips head screws you can slip the speedometer unit out of the case carefully. Now when you peer inside you will see 2 clips...one white and one red. Carefully push the little tab down and unhook both of these (tab shown in 4th image). Now you have separated the speedometer unit and we can begin to see why this is going to require a little electronic surgery...plus imagination. If you look inside the case you will see what remains is the GPS sensing unit (hot gun glued in place) and the power/ground connector (held by 2 more small phillips head screws). We'll leave those alone for now...

Okay, now for a little detective work. As you look at the speedometer unit, you'll see the problem. The Chinese gentlemen who built this used nice big electrolytic capacitors. Five of those installed right on the back side. And those two black things sticking up are microswitches...one of which controls the Mode (basically a selection mode for trip/reset/etc) and one of which controls the led lights (which we will not be powering). And the red and white connector plugs probably will be in the way. And finally you'll see an oval-shaped crystal. That might be in the way. We'll have to see about it. But the good news is these are pass-through connections and I suspect we'll find when we start removing the capacitors that we can flip them over and install them on the front side. And the better news is it seems all but one of them will fit (just barely...there will be about 0.5mm to spare between the top of the capacitors and the top plate.). I think one of them will strike the data display window and so we will have to lengthen the leads and mount that one laying sideways. Once that's done, I believe the thickness will be ok for the OEM case. If you look through and into the center, you'll see a black tube. This I think is to allow the special leds to channel their beautiful light right up to the dial plate.

That is about as far as we can go at this point, but more will follow later.

The black tube looks like a fairly standard light shield. It keeps the colored LED that is illuminating the needle from bleeding over into the face illumination. That is needed to allow the two to be different colors.

Can you get the part number off the GPS unit? That looks a lot like one that I experimented with for a vehicle tracker. When it worked it was great, but it was dooooooog slow getting satellite lock if it had been unpowered for more than about an hour.

Have you done any time to first lock tests on it yet? I am also curious if it has data smoothing in it.

Yes, it is a light shield for the leds. The number for that GPS module is MK 1612LF05. I have not been able to find much about it, but I haven't spent too much time searching. Please feel free and please let me know if you have data.

Okay...back to a bit more work here. What we need is free real estate on the back side of the unit...that is to say we can't have a bunch of electronic components sticking up all over the place. So we're going to flip those into the center...between the circuit board and the top plate. First, it is important to know these are classic electrolytic capacitors. That means these have a + lead and a - lead. We must observe that orientation if the unit is to work correctly. Usually the circuit board is marked to show the + or - orientation, but anytime I'm doing this I will mark with a red mark the - side so I won't get confused. You can see I've done that in the second image below. In the first image, I'm removing 2 phillips head screws that hold the circuit board in place. There will be a flex connector. Please move that back and forth carefully as you work. Now heat the front side of the circuit board where the capacitor leads go through with your soldering iron while applying gentle pressure first on one side of the capacitor and then on the other, wiggling as you go. After a few times of repeating this, you will have removed the capacitor. Use your soldering iron to remove any solder from the capacitor and straighten the leads. Now set the capacitor on the other (front side) of the circuit board in the proper +/- orientation and heat the solder dots until the leads come through and the capacitor is on the board. You may need to add some solder. You can see I've done this in the fourth image below. And on two of these, we're going to have to extend the leads and then lay the capacitors down instead of standing them up...one will hit a board-mounted component on the bottom side and one will hit the data screen if we don't do this. But the process is the same, so we'll take it slow and easy...have some ice tea with you and don't rush. In the fifth image below you can see I've soldered an inch or so of common solid copper wire (20 gauge) to the leads to extend them. Alternatively you could buy 2 new capacitors (which would arrive with long leads) and just use those.

Okay, I talked about laying two capacitors on their side. Please see image one below for the answer why. Image two below shows I've moved all 5 of the large capacitors inside along with the oval-shaped crystal over on the other side. Image three below shows I've left the crystal sticking up a bit off of the circuit board. There are a couple of tiny surface-mounted capacitors I didn't want the metal case to hit. And image four below shows the back side of the speedometer mostly cleaned up. You'll see I also removed the two micro-switches. I'll use one of these, but it will be simply 4 small wires connected to the circuit board with a switch sent off to another location. This will let us set/re-set the odometer. And one more thing, but not for today as I have an appointment with the eye doctor...I must remove and re-orient the white and the red plugs. They stick up too high and I want those oriented sideways for space-saving. Now one interesting thing. The black circle on the back side is a stepper motor. You might expect the needle shaft to be right in the center of the stepper motor, yes? Please look at it. The needle shaft is in the center of the speedometer but it sits about 1/3 of the way up from the bottom of the stepper motor. More about re-locating the plugs probably tomorrow or later. For now, we've accomplished a lot. We've turned this bulky and odd thing into a sleek compact speedometer that will fit into the stock housing nicely. Oh...important note...please do not remove the dial plastic. It has a clear window that will protect the data window until we're finished with our "surgery."

The steppers that they use in gauges are really high geared to get the resolution that they need to act as an analog gauge. That gearing is why the shaft is off to one side.

On a related note, the cheap steppers burn out after about 3 years, but if you replace them with the X25 version they will last a lot longer.

Fortunately this application will need very little torque. Hopefully that will work in its favor?

I would not expect to have a problem with the torque. Those same motors are used with 4" plastic needles, so the metal one in an AD gauge should be fine.

Just discovered this thread and am following. Was considering taking an ABS tone wheel and sensor off a worn out Aztek wheel bearing and seeing if it could be made to fit the hub of my bus. Then I'd have a tone wheel and sensor I could read, and I must admit I was inspired in this by the lowly VW Beetle, which has a cable that's turned by a front wheel as it spins. Anyway after I had that, I could rig up a stepper motor to turn the bus original speedo needle, after sussing out how many counts per revolution and how many revolutions per mile. That way the front wheel (speedometer sensor) always turns the same, versus the transmission output shaft which can turn at 5.57:1 or 7.8:1 depending on high or low rear axle range. There was a little switching gear reduction adapter from the factory, but it was disconnected when I got the bus in 1993 so I never had much hope of it working. If I really wanted to, I could even make a little motor that physically turns the original speedometer which does still work. Then I'd even have odometer. There's lots of room behind the dash, I think I like this idea.

Failing the sensor tone wheel, I could also just cut out the correct hole diameter into the center of a steel bicycle chainwheel, which would give me whatever number of teeth I needed. I could do it to each side then put ABS on my bus :-D

Hi Tronman,
Interesting approach you've mentioned. If you could post an image of the speedometer it is possible a GPS unit could be adapted to work. Please let us know.