TD5 Speedo Mileage run up circuit

[aaron_h]

Right were do we start...... Firstly my appologies if this has already been covered in the forum and iv not seen it.

Im following in the footsteps of the retroanaconda and his good work on investigating installing TD5 instrumentation and Speedo into older defenders so you can see your gauges at night.

Only the speedo I got off ebay had 64k on it and my 90 has 97k. I like to keep things right so decided to up the mileage to 97k. Some dont bother, some take photos for the history of the vehicle. Others look and either say dont go out at night or if it aint broke dont fix it.

Some may even send there speedo to ETB instruments or digi dash or what ever they are called these days and pay to have the reading changed. (This is the only way I know of to have the mileage reduced)

Firstly the speedo transducer.... How do we replicate its signal... What does it do.

In short the "A" pin of the speedo transducer connects the signal wire from the speedo to earth 4 times per rev of the transducer. so one 360 of the transducer goes N/C earth N/C earth N/C earth N/C earth. this can be confirmed using a multi meter and putting it on beep test connecting one lead to earth and the other to the wire connected to the A pin and spinning the transducer in your hand. The transducer will need powering up for this.

I read else where in this forum that the transducer gives 4100 pulses per mile.

Iv read about people putting the end of a transducer in a drill to spin the mileage up which seems like a good idea untill you need to add more then a couple of thousand miles to it.

Knowing the the transducer connects the speedo to earth to pulse it mad my task easier as i had some components in my electronics draw that specialised in connecting things to earth. up to something daft like 34v and a fair few milliamps. I also had a PIC Micro controller and an EASYPIC 6 development board. so i wrote a small program to turn on and off a pin on the pic chip about every 7 milliseconds which i worked out should be about 120mph on the speedo.

My code in Mikrobasic for pic

Program Speedo

main:

ANSEL = 0 ' configure AN pins as digital I/O

ANSELH = 0

TRISC = 0 ' set PORTC to be output

PORTC = 0xAA

portC = 0

while true

PortC.0 = 1

delay_ms(1)

portC.0 = 0

delay_ms(2)

wend

end.

Now in the above code the ms delays are less then 7ms and the reason is because when i powered it all up the speedo showed less then 50mph. I put this down to me running the chip with its internal clock rather then a 8 or so mhz oscillator which would be more accurate. anyway the above settings give just over 120mph. This should give me my desired mileage in a week or so. (im not in any rush)

The components you will need to make this circuit are....

1x PIC16F887 ebay or maplins

1x ULN2803 (18pin chip) ebay

1x tripad board from maplins

oh maybe some connectors if you intend to make it re usable... there again you could solder your link wires directly to the board it wouldnt make alot of difference.

I run this from a power supply that gives out 5v and 12v. if you dont have one of these look at adding a "7805 voltage regulator" available from ebay or maplin this will give you the 5v to run the pic chip. perhaps you could power it from a 240v ac to 12v DC adaptor

when the PIC pin is turned on the ULN2803 connects the speedo pin to earth.

[aaron_h]

Above; circuit on tripad board with some link wires etc

Speedo running at 120mph+ been going afew days now much quieter then a drill.

[kiwi_110]

Good job. But I need to run up 315,000 (!) k's on my new VDO speedo, so it matches my Road User Charges distance (don't ask...). Even at 200 kph that'll take 65 days! A local speedo shop will do it for $160. That's about 80 of your real, actual, genuine, British pounds. There are some points on the cct that give direct access to the EEPROM.

Ray.

[mickeyw]

Nice work Aaron, and thanks for sharing it on here. Maybe this thread could be added to the tech archive - Mods???

I, like Kiwi Ray could do with adding many more miles, around 110k miles in my case. It only shows 13k odd when installed, vs the 120k the truck had already done.

I am not a total electronics dummy, I understand what you've done, and could construct the circuit, although I'd have to chat up a mate to do the programming.

Now I know 7ms is a pretty small time gap, but can this be done any faster, or is this limited to the maximum speedo range? I can't tell in your program what you'd tweak to change the speed. OK, I can see the 2ms delay, but not sure how that affects what - like I said - just a partial electronics dummy

[kiwi_110]

Some programmable speedos can be fudged to speed up the process, you set them for a very low Pulse Per Mile (or Kilometre) rate, say 500 which might only be 10 pulses per second, then hit it with a much higher frequency, say 5,000/sec from your source the miles will clock up pretty quick. I dunno what happens to the needle mechanism though!

Ray.

[aaron_h]

I am not a total electronics dummy, I understand what you've done, and could construct the circuit, although I'd have to chat up a mate to do the programming.

Now I know 7ms is a pretty small time gap, but can this be done any faster, or is this limited to the maximum speedo range? I can't tell in your program what you'd tweak to change the speed. OK, I can see the 2ms delay, but not sure how that affects what - like I said - just a partial electronics dummy

In my program to make it run faster you would adjust the value in the brackets in the "delay_ms()" lines. cant drop them much lower but if you needed more pulses per second mikrobasic has a delay_us() command which stands for microsecond. there are 1000 microseconds in a millisecond. could be worth a try. Going back to the TD5 Speedo. I dont know the max pulses it can handle per second.

If anyone can flash a pic chip i have a hex file you can use with the above program. We aint allowed to upload .hex files so i would have to email it out

Some programmable speedos can be fudged to speed up the process, you set them for a very low Pulse Per Mile (or Kilometre) rate, say 500 which might only be 10 pulses per second, then hit it with a much higher frequency, say 5,000/sec from your source the miles will clock up pretty quick. I dunno what happens to the needle mechanism though!

Ray.

very good point for programmable VDO or the like.

What you were saying about the eeprom, on the back of the TD5 unit there is a well recessed 3pin port which i am guessing is the program port. However i wouldnt like to tamper with that because i dont know how its wired and i cant talk eeprom. It would be nice to undertake correcting the mileage ourselves the quick way... but then i suppose we risk never buying a genuine mileage TD5 in the near future. haha.

[CwazyWabbit]

I'd guess the mileage is stored in either an I2C or an SPI eeprom (which is very simple to read and write to without removing from the board), I was looking for a cheap TD5 speedo to take apart so I could work out what else was stored on the eeprom.

You hear stories of these being converted from MPH to KPH but keeping the same face/dial so I would guess this is also possible via the eeprom and maybe even calibration to allow for tyre size.

I had hoped to work this out and post to the forum but I haven't found a cheap one yet and also I'm getting the feeling a lot of people don't want this information out there, personally I think all the dodgy people out there probably already have the information anyway.

How do people on this thread feel about publishing such information?

[Retroanaconda]

If you can do it, then go for it I say. Would be very useful!

I have a Td5 speedo you can borrow, but I'd like it back in one piece when your done

[CwazyWabbit]

I'll take you up on that offer if you are serious, I have a number of different programmers here that we use when reverse engineering at work.

Not having seen a TD5 speedo close up do they look easily openable? I'd be fairly confident about not breaking it, I'll back up the eeprom contents before modifying anything so even if I fail I can return the speedo to you as it was.

In fact I'll offer you the guarantee that if I break your speedo or return it in a condition you are not happy with then I will source you a replacement, would that be a deal you'd be happy with?

[Retroanaconda]

PM Sent

[aaron_h]

Not having seen a TD5 speedo close up do they look easily openable?

Dont let the three torx head screws in the back fool you. These things just dont fall apart. I did remove them. but couldnt get the back cover to move. didnt want to risk breaking mine so went the long way and hence the run up circuit.

A photo of the back cover. there is a seam right around the edge suggesting that the back cover comes away.

[kiwi_110]

on the back of the TD5 unit there is a well recessed 3pin port which i am guessing is the program port.

Yeah, that's sort of what the VDO has, I believe the TD5 speedo is a badge engineered VDO unit.

[aaron_h]

Yeah, that's sort of what the VDO has, I believe the TD5 speedo is a badge engineered VDO unit.

Probably, however land rover got VDO to implement afew other features to solve a few niggles for TD5 models. These were a fuel guage damper circuit which also drives the low fuel warning lamp. So no more fuel light at half a tank on a roundabout

I believe there is some cirucit in there to read the temp sender from a 300tdi and control the td5 style temp guage.... but iv not got that far yet.

also it contains an alarm warning LED which i would also like to use on mine to save drilling holes in my new binnacle. Im not sure if this needs 12v or what and i dont know what voltage my current alarm LED is running at. More to come on this when i finally get round to it.

[CwazyWabbit]

Dont let the three torx head screws in the back fool you. These things just dont fall apart. I did remove them. but couldnt get the back cover to move. didnt want to risk breaking mine so went the long way and hence the run up circuit.

A photo of the back cover. there is a seam right around the edge suggesting that the back cover comes away.

Does the seam look glued?

If I can't get it apart someone mentioned there looked like a 3 pin programming port. I could connect up a logic analyser to see if I see a recognisable protocol in use and work from there, so it isn't a total disaster if I can't look inside, just means it will take longer.

[Retroanaconda]

Probably, however land rover got VDO to implement afew other features to solve a few niggles for TD5 models. These were a fuel guage damper circuit which also drives the low fuel warning lamp. So no more fuel light at half a tank on a roundabout

I believe there is some cirucit in there to read the temp sender from a 300tdi and control the td5 style temp guage.... but iv not got that far yet.

also it contains an alarm warning LED which i would also like to use on mine to save drilling holes in my new binnacle. Im not sure if this needs 12v or what and i dont know what voltage my current alarm LED is running at. More to come on this when i finally get round to it.

There is a circuit for the 300Tdi temp sender, used on ROW-spec models that used the Td5 dash. It's simply a resistor which the sender signal is passed through to alter the value to suit the Td5 gauge. Nothing more advanced than that

The alarm LED is switched via earth I believe, it's on one of the pins of the speedo plugs. I can't remember which one off-hand, but I'll dig out my info tonight for you.

[aaron_h]

Does the seam look glued?

If I can't get it apart someone mentioned there looked like a 3 pin programming port. I could connect up a logic analyser to see if I see a recognisable protocol in use and work from there, so it isn't a total disaster if I can't look inside, just means it will take longer.

I think it maybe glued. The 3 pin programming port is at the bottom of the rectangular hole above the RH bulb holder in my photo. looks like 3 pcb header pins soldered to some wire and poked down the hole would work

There is a circuit for the 300Tdi temp sender, used on ROW-spec models that used the Td5 dash. It's simply a resistor which the sender signal is passed through to alter the value to suit the Td5 gauge. Nothing more advanced than that

The alarm LED is switched via earth I believe, it's on one of the pins of the speedo plugs. I can't remember which one off-hand, but I'll dig out my info tonight for you.

That would be most helpfull, although i guess its already on your tech post about fitting the new style instruments, i dont mind looking over that again... but for others who stumble upon this post it would be good

[FridgeFreezer]

Wow, microcontrollers on a LR forum - careful, you'll get burned as a witch!

Alternative to PIC etc. is a 555 timer or even a 2-transistor oscillator (astable multivibrator sir? ).

[mickeyw]

I'm sure modern LRs are woefully full of the wretched things

But would you mind explaining how these alternative methods can be used? For us wannabee electronics dummies.

I once built a gadget using a 555 for an interior light delay device, but someone far cleverer than me drew up the circuit

[Retroanaconda]

A 555 astable circuit could be used to pulse the speedo and emulate the transducer so as to produce a speed signal. It would just require the right combination of capacitor and resistor. Been a while since Electronics at school but I reckon I could still build one.

Mr Wabbit is going to see if it's possible to interface direct with the EEPROM chip in the speedo, which would remove the need for such things. Of course it's possible as Digidash etc. all do it, but how it's done isn't commonly known. Yet

[Mo Murphy]

I bought some 555 cigarettes once, does that help ?

It's nice to see forum members coming together to resolve a problem or make an improvement and it's nice to see there's still work to go in the fitting of a TD5 dash. As an aside 4 or 5 years ago before it was known how easy it is to fit the TD5 speedo, I bought 2 brand new TD5 speedos on ebay from different sellers for £15 each One went in my last 90 and the second I've fitted to the current rebuild

Mo

[FridgeFreezer]

Since this is my day job, if you get any info on the internals or need any pointers then just ask, I2C and SPI are no problem. I'm off on holiday for ~2 weeks after tomorrow so don't hold your breath for a quick reply though. Check out the BusPirate from Dangerous Prototypes, if there is any sort of communications going on it will sniff it out & let you tinker with it.

A 555 is a very simple timer, there are a squillion reference designs out there for it, you just need it to run as an oscillator, one of its most common uses. There will be reference circuits & calculations in the 555 data sheet. The Megasquirt Stimulator board is a basic variable-speed 555 oscillator that should get you 99% of the way there.

You can do the same thing with two transistors, almost any book on electronics should turn up a circuit for you, as should google with the usual caveats about enthusiastic amateurs

[crclifford]

I think it maybe glued. The 3 pin programming port is at the bottom of the rectangular hole above the RH bulb holder in my photo. looks like 3 pcb header pins soldered to some wire and poked down the hole would work

When i got Digidash to sort my Td5 speedo out, he bent the black metal ring back at the front of the dial to get the back off the speedo.

So i would suggest removing the torx screws and then bending the metal ring back to see if it comes apart.

If i do take my binnacle off soon i will see if i can get photos/look at to see if i can see what he did.

HTH

[CwazyWabbit]

When i got Digidash to sort my Td5 speedo out, he bent the black metal ring back at the front of the dial to get the back off the speedo.

So i would suggest removing the torx screws and then bending the metal ring back to see if it comes apart.

If i do take my binnacle off soon i will see if i can get photos/look at to see if i can see what he did.

HTH

Cheers for that info, sounds like the way I went about dismantling the VDO tacho I checked out previously.

Interesting that digidash take what I would have thought is a heavy handed approach, although the back of that ring is well hidden when it's inserted back into the binnacle.

[CwazyWabbit]

Since this is my day job, if you get any info on the internals or need any pointers then just ask, I2C and SPI are no problem. I'm off on holiday for ~2 weeks after tomorrow so don't hold your breath for a quick reply though. Check out the BusPirate from Dangerous Prototypes, if there is any sort of communications going on it will sniff it out & let you tinker with it.

A 555 is a very simple timer, there are a squillion reference designs out there for it, you just need it to run as an oscillator, one of its most common uses. There will be reference circuits & calculations in the 555 data sheet. The Megasquirt Stimulator board is a basic variable-speed 555 oscillator that should get you 99% of the way there.

You can do the same thing with two transistors, almost any book on electronics should turn up a circuit for you, as should google with the usual caveats about enthusiastic amateurs

Thanks for the offer of help on our group project Mr Freezer Sounds like we are back at school

Hopefully we'll have results before you get back from Holiday... but if we don't then we may be knocking on your door!

[western]

When i got Digidash to sort my Td5 speedo out, he bent the black metal ring back at the front of the dial to get the back off the speedo.

So i would suggest removing the torx screws and then bending the metal ring back to see if it comes apart.

If i do take my binnacle off soon i will see if i can get photos/look at to see if i can see what he did.

HTH

I sent mine to Digidash, it came back exactly as I sent it, no damage whatsoever, just increased the total mileage reading to exactly as requested.

This thread now linked to the Tech Archive.very interesting information, well done guys.