So I have a 94 model FZJ80, this version uses the 3 pin electronic VSS (Vehicle Speed Sensor) attached to the side of the transfer case. It has 33inch tires on it and as a result the car is actually going faster than the speedometer says it is. Being that my wife and kids will be driving the car I wanted to solve the speedo calibration to the tire size issue once and for all. I did a bit of searching on this forum and found that the Silicone Chip Magazine produced, Jaycar distributed Speedo Corrector MK I and MK II (Speedo Corrector MkII Kit | Jaycar Australia - https://www.jaycar.com.au/speedo-corrector-mkii-kit/p/KC5435) seemed to work really well for people that tried it. There were a few posts about the MKIII (both kit and final assembly version) not working at all, but I couldn't substantiate it.
Being that the kit was release with through hole technology in 2004, and the MK II subsequently in 2006, I have been thoroughly unable to source any kits, any versions of the circuit boards in production or anything else. I was able to source the programmed PIC for the Mk II directly from Siicone Chip, and I have a copy of the 2006 magazine article lying around as well).
For us Aussies, all of the current after market options available to us seemed to be at the $200 USD mark and need to be shipped from overseas, and that's just too much to spend for a "simple" PWM circuit in my mind (I'm an electrical engineer by trade).
I did manage to source an MK III unit (Speedo Corrector Module for Cars | Jaycar Australia - https://www.jaycar.com.au/speedo-corrector-module-for-cars/p/AA0376, at $65 + shipping from a regional jaycar) and verify that it indeed doesn't work, no matter what you do to it (I've concluded there must be a bug in the PIC firmware for that component as I was unable to get any response out of it), and was about to shell out $200+ for one of the alternatives when I decided to turn this into a learning experience...
Given that Silicone Chip still supplied the programmed PIC chip, and the PCB pdf file (for free no-less), I was going to try and get the board assembled and build it from the components myself.
This didn't work out too well, as no one prints PCB's using PDF's anymore everyone wanted a gerber file. So I dove down that rabbit hole and spent a few weeks re-learning schematic and PCB design (in kicad) and eventually sent off a my version of the Speedo Corrector MK II circuit board to be produced by JLCPCB. The minimum order run was for 5 boards, so I actually have enough to make 5 of them.
I assembled the board, added the PIC and chucked it into the 80 Series, and it actually worked first go. I'm happy to say it's in the car permanently now, with no complaints, except for the surplus of 4 extra boards I didn't really need. I even went so far as designing and 3d printing an enclosure for it (photo below)
I didn't actually stop there though, I decided that I didn't want to depend on a potentially obsolete PIC going forward, so I brushed up my assembler skills, and migrated the firmware from the PIC across to an Arduino Nano, and while I was at it I improved the power supply filtering and output circuits and migrated the design over to SMD technology significantly shrinking the board size. I've verified the arduino firmware in simulated circuit tools (simulide) and have ordered some nano's to check it in the car shortly.
When this is verified, I will probably go back out and get the SMD boards manufactured as well, but right now, given the first (through hole) version of my boards worked so well, I can't really justify the time/expense to do that.
All in all it's been an intense few months, and quite an enjoyable refresher in analog and digital design.
Being that the kit was release with through hole technology in 2004, and the MK II subsequently in 2006, I have been thoroughly unable to source any kits, any versions of the circuit boards in production or anything else. I was able to source the programmed PIC for the Mk II directly from Siicone Chip, and I have a copy of the 2006 magazine article lying around as well).
For us Aussies, all of the current after market options available to us seemed to be at the $200 USD mark and need to be shipped from overseas, and that's just too much to spend for a "simple" PWM circuit in my mind (I'm an electrical engineer by trade).
I did manage to source an MK III unit (Speedo Corrector Module for Cars | Jaycar Australia - https://www.jaycar.com.au/speedo-corrector-module-for-cars/p/AA0376, at $65 + shipping from a regional jaycar) and verify that it indeed doesn't work, no matter what you do to it (I've concluded there must be a bug in the PIC firmware for that component as I was unable to get any response out of it), and was about to shell out $200+ for one of the alternatives when I decided to turn this into a learning experience...
Given that Silicone Chip still supplied the programmed PIC chip, and the PCB pdf file (for free no-less), I was going to try and get the board assembled and build it from the components myself.
This didn't work out too well, as no one prints PCB's using PDF's anymore everyone wanted a gerber file. So I dove down that rabbit hole and spent a few weeks re-learning schematic and PCB design (in kicad) and eventually sent off a my version of the Speedo Corrector MK II circuit board to be produced by JLCPCB. The minimum order run was for 5 boards, so I actually have enough to make 5 of them.
I assembled the board, added the PIC and chucked it into the 80 Series, and it actually worked first go. I'm happy to say it's in the car permanently now, with no complaints, except for the surplus of 4 extra boards I didn't really need. I even went so far as designing and 3d printing an enclosure for it (photo below)
I didn't actually stop there though, I decided that I didn't want to depend on a potentially obsolete PIC going forward, so I brushed up my assembler skills, and migrated the firmware from the PIC across to an Arduino Nano, and while I was at it I improved the power supply filtering and output circuits and migrated the design over to SMD technology significantly shrinking the board size. I've verified the arduino firmware in simulated circuit tools (simulide) and have ordered some nano's to check it in the car shortly.
When this is verified, I will probably go back out and get the SMD boards manufactured as well, but right now, given the first (through hole) version of my boards worked so well, I can't really justify the time/expense to do that.
All in all it's been an intense few months, and quite an enjoyable refresher in analog and digital design.
