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200 Series General Forum for the Volvo 240 and 260 cars |
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Volvo 240 - Electronic Mileage CorrectionViews : 2349 Replies : 7Users Viewing This Thread : |
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Oct 30th, 2022, 17:20 | #1 |
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Volvo 240 - Electronic Mileage Correction
Hi all,
More of a novelty thing than being crucial to running, but I did find a method of correcting the odometer mileage electronically. This might be useful if your odometer gear has been broken for a while (like mine was for ~2k miles over summer). I followed the instructions on Dave's Volvo Page for the odometer gear repair in my 1990 240 GL B200F Auto. I opted to (and recommend to) follow the "procedure with speedo needle in place" section - there is more than enough room to access everything. Anyways, onto the mileage correction: some people suggest clicking the cogs forward by hand using a small screwdriver or similar instrument; however, I was afraid of snapping/stripping other cog teeth in the process of doing this. Instead, I opted to tap into the speed sensor signals (the one that resides on the rear axle) in order to clock the odometer forward electronically, thus removing any risk of damaging any of the other cogs. To do this I tapped onto the speedo board in the places shown in the attached photo (I even used the correct wire colours as well - go me 😁). I opted to solder some wires onto the board and desolder them before refitting the speedo unit (less chance of slipping and shorting something) - although one could feasibly use some crocodile clips to achieve the same purpose. I then 'spoofed' the speed sensor signal using a square wave alternating between 0V and 5V. To create the square wave I used an Arduino, although other circuits are available for creating this using a 555 timer, an op-amp relaxation oscillator, or even a two-transistor astable multivibrator circuit. I can post schematics of all the above if people would like. With regards to the frequency of the square wave, the maths appears to be as follows:
As a worked example (and with video evidence to prove it, if requested):
Thus I'd recommend a frequency of approximately 300Hz - 350Hz to make decent progress clocking up mileage. I will share the Arduino code in a zip file, along with schematics for all 4 aforementioned approaches in a separate post coming over the next day or two. For now, I will just attach the images showing the speedo connections. Also note, two pins on one of the speedometer connectors need to be shorted in order for the speedometer + odometer to work at all. In my photo, the inner-most and centre positions need to be shorted. DO NOT touch the outer-most position - I think this may be to do with cruise control or something and will probably fry the unit if you connect it to anything. Alternative Link: https://drive.google.com/file/d/1sNk...ew?usp=sharing
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1990 Volvo 240 GL Auto "Catalyser" (oOOoh, fancy). B200F, about as original as they come, and all in BLOO. ~140k
My electronics website/blog thing: https://unintegratedcircuit.wixsite....egratedcircuit Last edited by TheHungriestBadger; Oct 30th, 2022 at 20:19. Reason: Added Google Drive permalink to attached image |
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Nov 11th, 2022, 02:47 | #2 |
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Wiring Colour Update:
Slight update to the wiring colours:
For my vehicle - a 1990 Volvo 240, with electronic speedometer, without ABS, and with the large tachometer instead of the clock - there is a 3-pin white L-shaped connector (see attached image) that plugs into the back of the instrument cluster, near the middle IIRC. The connector is keyed, so no possibility of getting it the wrong way around. The pinout is as follows:
In my photos, you will see I've matched BLUE with blue, GREEN/WHITE with solid green, and BLACK with brown, as these were the best matches I had to hand. Obviously wire colour makes no difference electrically, but I felt it was worth clarifying. From here on out, I will be referring to wire colours as per MY wiring colours, rather than the colours on the connector. Alternative Link: https://drive.google.com/file/d/1bQW...usp=share_link
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1990 Volvo 240 GL Auto "Catalyser" (oOOoh, fancy). B200F, about as original as they come, and all in BLOO. ~140k
My electronics website/blog thing: https://unintegratedcircuit.wixsite....egratedcircuit |
Nov 11th, 2022, 15:38 | #3 |
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Two-Transitor Multivibrator Schematic
Possibly the simplest circuit in terms of components required, this uses only two transistors in an astable multivibrator configuration. This circuit will not be terribly accurate with the frequency it produces due to component tolerances (1% - 5% on resistors, 20% or more on the capacitors, plus potential mismatch on transistor current gain). Fortunately, accuracy is not critical here.
Values were determined using a simulation program called LTSPICE - which is usually pretty accurate - and the values used here generated a 5V square wave with a frequency of 310Hz. Rearranging the formula derived in post #1, this should correlate to a speed of approximately 114mph. The transistor choice is not critical, any generic NPN transistor will do, although the BC547 is the defacto standard in my region. American viewers will likely have the 2N2222 or the 2N3904, both of which are suitable replacements. Resistors can be either metal-film (1% tolerance) or carbon-film (5% tolerance) and can be of any power rating. Capacitors should be non-polarised, the most common type fitting the requirement are ceramic capacitors; any dielectric and voltage rating is suitable here. Finally, the regulator choice is also not critical, either a 7805 or 78L05 (L standing for Low power applications, compared to the standard part) will work just fine. You may be able to get away without using the capacitors C3 and C4; however, if the 5V output is not stable for whatever reason, the capacitors C3 and C4 should fix this issue. Alternative Link: https://drive.google.com/file/d/1GZ2...usp=share_link
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1990 Volvo 240 GL Auto "Catalyser" (oOOoh, fancy). B200F, about as original as they come, and all in BLOO. ~140k
My electronics website/blog thing: https://unintegratedcircuit.wixsite....egratedcircuit |
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Dec 30th, 2022, 04:54 | #4 |
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555 Timer-Based Schematic
Another possible implementation is to make a circuit based on the ubiquitous 555 timer chip. This is an adaptation of the standard 'astable' circuit, which produces an output wave that is more or less 50% 'high' and 50% 'low' - this is known as having a 50% duty cycle.
Again, the circuit was simulated in LTSPICE, and the circuit generated a ~5V square wave with a frequency of 295Hz. Again, expect this to change slightly due to the usual component tolerances. This equates to a speed of approximately 108mph for my K9800 speedo. Some important notes on the schematic: first off, yes the diode is the 'correct' way round. It's a special type of diode called a Zener diode, which is designed to conduct in a controlled manner when placed in reverse. I'll spare you the electronics lecture for now (this information can always be Googled), but suffice to say, in this circuit, it acts to cap the voltage of the produced square wave. This can be substituted for any other Zener diode part number as long as it is a "5.1V" or "5V1" part - that's the important factor. Secondly, yes the resistor values do need to be followed, unfortunately, as annoying as it is. Thirdly, you can probably get away with connecting pin 4 of the NE555 directly to pin 8 (positive supply), omitting resistor R3, but if things start to go wrong, this could be a cause. Finally, capacitors C2 and C3 can also probably be left out without consequence, but again, I try and do these circuits as properly as possible to prevent people having issues if they decide to reproduce it exactly. Alternative Link: https://drive.google.com/file/d/1Lla...usp=share_link
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1990 Volvo 240 GL Auto "Catalyser" (oOOoh, fancy). B200F, about as original as they come, and all in BLOO. ~140k
My electronics website/blog thing: https://unintegratedcircuit.wixsite....egratedcircuit |
Dec 30th, 2022, 06:05 | #5 |
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Using An Arduino
If you wish to take the exact same approach I did, then you will need the following:
And the methodology:
If everything worked as I think it should've done, you should have your speedo sitting well above 100mph. Congrats, now just leave it be and check back every now and then. Bear in mind that you can't roll it backwards you'll have to wait for it to go right around again. Should you wish to run it at a slower speed, just increase the number inside the Code:
delayMicroseconds() I think it's also worth noting that the code itself can't really harm your speedo, but the physical connections can. As with all these solutions: just double-check your wiring first with a multimeter. Is there a short between positive and ground? Is there a short between positive and signal? Is there a short between signal and ground? Give the speedo board a quick once over, are there any splashes of solder? Are the wires soldered properly (give it a 'gentle but firm' tug test)? If you've opted for crocodile clips, are they secure, or are they likely to slip and short? Is there anyone else around who could move the setup (maybe add a "do not touch" notice). Patience and caution go a long way with this kind of electronics, these are (relatively) quick and dirty setups, and do not have the usual rigorous protection of typical automotive electronics. Alternative Link: https://drive.google.com/file/d/1iUx...usp=share_link
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1990 Volvo 240 GL Auto "Catalyser" (oOOoh, fancy). B200F, about as original as they come, and all in BLOO. ~140k
My electronics website/blog thing: https://unintegratedcircuit.wixsite....egratedcircuit |
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Feb 6th, 2023, 10:09 | #6 |
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Tutorial Video
Well guys (and gals), today is your lucky day: my junkyard odometer gear sheared its teeth early January and I've just got around to replacing it.
Between my all my rambling, it managed to stretch the video to 30 minutes so get a cup of your favourite beverage in advance; however, if you only wish to know about the electronic rolling forward of the mileage, I'm pretty sure it's only the second half of the video. But yeah, it (should be) live now at the following link, so enjoy. https://youtu.be/sBc2NeJ9_BQ
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1990 Volvo 240 GL Auto "Catalyser" (oOOoh, fancy). B200F, about as original as they come, and all in BLOO. ~140k
My electronics website/blog thing: https://unintegratedcircuit.wixsite....egratedcircuit |
Jan 7th, 2024, 23:29 | #7 |
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Electric mileage Correction Different Speedo
Thank you for your generous content on YouTube and here on this Forum. I’ve studied the videos and your posts. I was given an extra speedo from a friend’s collection to fix and use. Unfortunately, the circuit board is different from the one referenced in your posts. I’ve searched for the schematic online with no success. The speedo model is VDO 992 645 (145) beneath. I’m unable. To attach a photo or I would do so. Perhaps I can attach it to your YouTube video in comments. I am uncertain about where to attach the wires. Any assistance you can provide will be appreciated. Thank you!
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Jan 7th, 2024, 23:49 | #8 |
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Glad to hear I'm useful to someone :) if you want, I can PM you my email address and you can send me the photo that way? You won't be able to attach it in YouTube comments, unfortunately.
I'm not familiar with individual speedo models, but if you can give me any other information on your car that might help myself (and others) point you in the right direction. For example, I know certain years/specs/transmissions, etc. had cable-driven speedos which obviously won't be electronically controllable but may still have had a PCB attached? |
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240, mileage, mileage correction, speedo, speedometer |
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