Classic Mini 1275GT Electronic GPS Speedometer and multifunction display.

The Mini 1275GT is fitted with a mechanical speedo. It is pushed from an output on the gearbox through a cable, which wings it is method throughout the again of the engine bay, by way of the bulkhead and into the speedometer itself. The cables at all times appear to get cooked by the warmth from the exhaust manifold, and fail pretty typically. I’ve obtained sick of fixing them ….
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The 1275GT’s speedo reads (slightly enthuiastically) to 120 MPH…..
….. and is dear resulting from it is rarity
Absolutely there’s a greater strategy to drive it??

Plan A…
Get a damaged speedo cable and harvest the speedo drive becoming, connect that to a small electrical motor, and use that to spin the speedo drive to indicate the proper velocity. Get the velocity from a GPS module, PWM the motor to indicate the proper velocity. Even the odometer will run appropriately.
The speedo is marked 1248 TMP on the dial… this implies it wants 1248 turns per mile.. So at 60MPH that is 1248 RPM, and at 120 MPH, 2496 RPM… so a 2,500 RPM motor could be glorious.
A small motor and gearbox was procured from eBay…
Electronic Repairing   oh it IS small!
Electronic Repairing   The tip was faraway from a speedo drive cable ….
Electronic Repairing   … and hooked up to the shaft of the motor’s gearbox…
Working some checks confirmed the motor would drive the speedo, but it surely was going to wish some kind of suggestions to stabilise the velocity… after which it turned very apparent that this tiny motor was not going to be man sufficient to drive the speedo for any size of time at any velocity… it was VERY sizzling.
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I seemed within the junque field and located a couple of different motors….
This seemed promising, however was too lumpy at low speeds… an analogous motor was additionally examined with comparable outcomes. Disgrace because the torque supplied by these motors was ok that velocity management wouldn’t be required.

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I then discovered this magnificence, with a tacho so I might create some suggestions to precisely management velocity…

Throughout checks it seized up 🙁

What a few stepper motor? … nah not at 2,500 RPM 🙁

It turned obvious that this was going to be difficult…

Plan B …..

Strip the speedo down, and exchange the mechanical drive with a mannequin servo…

Electronic Repairing   Benefits… Simple to drive.

Disadvantages …
Odometer will not work (exchange with an LCD or OLED show?)
Means gutting an costly instrument.
Positional 270 (or larger) servos are costly, and have questionable positional accuracy.

… no less than an “unusual” 90 MPH speedo might be required for observe!

A budget 360 diploma servo proven isn’t any use, it is a “steady rotation” servo, which has no positional suggestions in any respect. It merely turns somehow advert infinitum. To implement a positional servo, we would want an costly “boat winch” servo.

I am not eager on this concept….

Plan C….

Electronic Repairing   A stepper motor to drive the needle.

Simple to drive (may have an H-bridge), cheap. Correct (particularly a geared down unit)

Might want to get a zero place, one thing like a leaf or microswitch to set zero. Will want a show for the odometer.

OK, this seems to be possible….

I had a pleasant cup of tea, and a little bit of a assume …. how does the speedo and rev counter work in Mrs Doz’ posh Audi?

Whenever you change the ignition on in her automotive, the speedo and rev counter transfer to the total scale place, after which to zero earlier than settling right down to the proper studying .. have to be pushed by some kind of motor ….

After some googling, it seems that producers use a particular instrument stepper motor to do that!

Electronic Repairing   Vauxhall have one which’s VERY low cost!

It is referred to as the X27.168, and I purchased 6 (Sure 6!!) for change out of a tenner on eBay! … and a few blue LEDs (unsure what I will do with these!)

Not solely that, however there’s an arduino library at
which can drive the issues, and with out an H-bridge! Oh pleasure!

Electronic Repairing   Just a few feelers have been put out for a gash speedo I might use as a check mattress, and Tim at MiniMail (an outstanding purveyor of traditional Mini elements) turned up a little bit of an oddball speedo.

Look fastidiously on the image, the KM/H and MPH scales are the identical! It is a continental 1275GT speedo with a UK bezel. A perfect candidate.

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I additionally ordered a 0.91″ I2C OLED show to exchange the odometer.

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The bezel was eliminated (usually there could be a bit of glass over this, but it surely was lacking)….

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… the 2 screws both facet of the speedo drive becoming was eliminated ….

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… adopted by the mechanism.

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Electronic Repairing   The pointer was fastidiously eased off the shaft…

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… and the 2 screws holding the face to the remainder of the mechanism eliminated. Notice the state of the screws. It could seem I am not the primary to have been right here!

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Face off….

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Take away the 2 screws all sides of the assist bracket.

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Unsolder and take away the return spring.

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Take away the 2 high and backside screws and separate the magnetic coupling. The spindle drive and plate can now be eliminated….

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… leaving the odometer digits.

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Separate the break up washer from the top of the shaft and take away the gears….

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… and push the shaft out. Notice there might be some resistance right here, as there is a nylon break up washer between the top of the barrel and the bracket.

Take away the odometer barrel…

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Leaving us with a disassembled again plate.

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… and a pleasant clean canvas !

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I made a small gap in a cardboard field, so the zero cease pin on the face would sink in leaving me with a pleasant flat floor to work on. The OLED show is slightly brief, however in any other case seems to be to suit beautifully. I could make a bezel as much as cowl the shortfall…

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The rear bracket will want the barrel assist arms eradicating or shortening although…

Electronic Repairing   I hoped to get fortunate with the spindle measurement, however alas no. The mini spindle is slightly smaller than the brand new stepper motor…..

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Fortunately, there’s sufficient meat on the pointer to bore it out barely with a really superb drill…

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Though it is a good match, a spot of thread lock will cease it transferring as soon as remaining meeting is full.

Electronic Repairing   Subsequent job is to mount the stepper motor to the bracket. I secured the faceplate to the field to stop it from transferring about…..

Electronic Repairing   and punched a small gap within the useless centre of the show, to centre up the motor shaft…

As there are not any mounting holes within the neighborhood of the motor mounting holes, I decide to connect the motor to the bracket. Appropriate adhesives have been thought of … Tremendous Glue (cyanoacrylate), UHU “common glue”, Araldite (Epoxy) … all of those have been rejected. Tremendous glue could be too brittle, and it has a propensity to run the place you do not need it. I do not assume UHU might be robust sufficient, and Araldite appears to be a bit “runny” lately…. I seemed about for an alternate…. Epoxy automotive physique filler? Robust, not runny, units shortly if combined with a contact extra hardener than actually required… let’s give it a go!

Electronic Repairing   Place a small warmth shrink sleeve over the stepper motor shaft to stop it getting caught in any extra filler. We are able to take away this afterwards…

Electronic Repairing   Combine up a small quantity of filler, and apply to the bracket …

Electronic Repairing   … and place the motor fastidiously, so the shaft (and sleeve) push down by way of the cardboard field.

Maintain in place till the filer begins to set (Should you make slightly an excessive amount of, you’ll be able to see if it is set in your mixing board)

Electronic Repairing   Take away the protecting sleeve. Slightly filler has oozed up around the sleeve. I eliminated this with a pointy craft knife….

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… and the pointer check fitted. Seems good (should clear the corrosion off the centre although!) . Do not push the pointer on too arduous simply but, we’d like to verify the stepper motor is ready to zero first.

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Subsequent solder some wires to the rear of the motor…

Notice the pins aren’t numbered on the motor….
Type of commonplace conference would make pin 1 blue, pin 2 gray, pin Three white and pin Four purple… the colors aren’t essential, however connecting them as much as the proper ports on the Arduino is.

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We’ll use Digital pins 4,5,6 & 7 as they’re default for the library.

Pin 1 of the motor to digital pin 7 of the Arduino.
Pin 2 to digital pin 6
Pin Three to digital pin 5
Pin Four to digital pin 4

OK. Now we have to calibrate our pointer.

First off, setting the zero place. I could not get the instance sketch within the library to run. It could compile OK, however did not work as anticipated. So load this into your Arduino:-

This may set the motor to zero, run it spherical to half method watch for a second, after which again to zero.

Now push your pointer on (after you’ve got polished up the corroded bit!). Hit reset. It is best to have one thing like this ….

You will discover because the motor is discovering zero, it jitters a few bit. That is regular.

Now we have to calibrate the total scale deflection, on this case, 120 MPH.

Load up the next sketch …

Electronic Repairing   … and join a 10Ok pot, with the ends of the pot on 5V and GND, and the wiper to A1. Open the serial monitor window.

Whenever you run the sketch, the pointer will zero, transfer to the midway level, after which transfer to some extent decided by the place of the pot.

Once more, don’t be concerned concerning the pointer jittering a bit, the sketch and electronics are easy, and there isn’t any averaging on our analogue enter, so it strikes round.

Electronic Repairing   Flip the pot unit the Speedo signifies 120MPH.

Electronic Repairing   Learn the worth displayed on the serial monitor, and write it down. We’ll want it later. It is 784 in my case.

Electronic Repairing   Slightly black spray paint hides the blue PCB on the show properly. The show was wired up and examined…

Electronic Repairing   ..and punctiliously glued into place with a smear of UHU common glue to the raised a part of the faceplate. It was held there till the glue has set.

I briefly added some textual content into this sketch to jot down “THIS WAY UP!” to keep away from a mistake!

Electronic Repairing   While the glue made an affordable job of holding the show in place. It wasn’t fairly as much as the job. One other gob of physique filler sorted that …

Electronic Repairing   The speedo might now be reassembled.

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Nice, now for another {hardware}…

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The {hardware} wants slightly rationalization. The Arduino is linked to the show and GPS in a standard method, it is the facility provide that is slightly odd, and with good motive. 
When the unit is working, we do not wish to maintain updating the EEPROM with the mileage, because the EEPROM wears out slightly each time we write to it, so we’d like on solely write to it each time the automotive is switched off. Now I did ponder utilizing an interrupt, writing the information and placing the micro to sleep each time. I made a decision towards this due to the character of the autos provide. Throughout cranking the voltage may be going anyplace … spikes of 75V, voltage falling to six … usually disagreeable. When the micro wakes up, issues have to be regular so every little thing comes again up in an orderly method. We won’t assure this. 
This is the plan. When the automotive is initially switched on, The IGN line provides 12V briefly (for a break up second, till the starter is engaged) it then disappears…there’s  a 6-second delay initially of our sketch ready for the GPS to energy up, so nothing occurs. The micro will shut down once more. Now the engine is working, our IGN line returns, and provides energy to the 7805 through D3. The micro begins up, and runs it is arrange process. As soon as that is executed, the micro sends D8 excessive, switching the relay K1 through T1, and the 7805 is now getting it is energy from the everlasting 12V line. Any nasty spikes on the availability are handled by R3, and the 2 zener diodes, D1 and D2.
So we drive about for a bit, the speedo doing what it ought to. We cease, and change the automotive off. The IGN line goes low, and that is sensed by D9. This runs the shutdown routine, which writes our up to date mileage to the EEPROM, and sends D8 low, switching off K1, which kills the facility to the micro.
…. then I obtained to pondering. Within the automotive there’s an ashtray within the high sprint rail. It did extra for non-smoking within the UK in the course of the 1970’s than the entire authorities well being warnings put collectively… What a few good show there? We have already got GPS out there, so what a few digital speedo and a clock ? We might simply measure the battery voltage. Outdoors temperature could be good to fulfill the love us British have for moaning concerning the climate… 
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Battery voltage is learn by way of A0, through a voltage divider fashioned by R2 and R6. R6 can be utilized to regulate calibration. Temperature is supplied by a DS18B20 temperature sensor. Glorious. I used a separate micro to keep away from clashes, and reminiscence points (and, to be sincere, it was all a little bit of an afterthought!!) I additionally added some hyperlinks, so the serial interface might simply be disconnected when importing new software program throughout growth.
Electronic Repairing   The electronics was constructed up on a little bit of perfboard, and linked to some din plugs to connect with the varied elements. One every for GPS receiver, speedo (each motor and show), the “multi-function ashtray show”, and the temperature sensor.
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Should you simply needed so as to add the multifunction show, you possibly can simplify the facility provide (no relay or switch-over wanted), and simply use the second micro. You’d need add the auto-config half initially of the speedo sketch, and ship the arduino’s Tx line to the Rx pin on the GPS receiver as nicely)
Testing exhibits the speedo to be very correct towards one other calibrated unit, so I am happy with that. 
OK, so now I’ve obtained git, the software program (and the required libraries) may be discovered  at It is nonetheless right here within the little textual content field too, for all you copy’n’pasters…
Addendum 04-Sept-2017 – get the software program from the git hub web page above. I’ve made a couple of revisions to stop EEPROM corruption. The newest software program will at all times be out there on the git.

This is the sketch for the multifunction show (additionally out there from )

This is an exquisite video of it in motion!

*** STOP PRESS!!!*** I’ve now revised the software program barely… take a look at 

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