The LHD Digidash Bible

[Pyro15D]

Thank you, it is still a work in progress. I was able to interface it with my HKS EVC1 so it displays what boost setting I have as well. I can probably do a write-up on that if you guys want as well.

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[Grandavi]

I would so love to go digital (lots of pluses there... ) but after thinking about it, I kinda like the old skool feel of the sweeping dials.

Huge props though on doing an excellent job!

 

[Pyro15D]

Thank you sir. I felt the same way while working this project, which was why I did the conversion in such a way that if I ever want to swap back to the analog gauges, it won't take me more than half an hour. I soldered the new connectors onto the stock dash harness and figured out how to modify the stock fuel sender so it will work with the dash. Since running this though, I don't think I will go back to the analog gauges though. These respond way faster, especially the oil and boost gauges. If I run low on oil pressure, I want to know now, not 15 seconds after the fact haha!

 

[Grandavi]

That is the best thing, update speed and accuracy...

 

[Pyro15D]

Yeah, it is a good thing! My next order of business is to figure out what makes the digital dash dimmer different from the analog dimmer. The digital one has 6 pins but the analog one only has 3. They are both electronic, so I'm assuming that the lighting is dimmed via PWM. I read that the digital dimmer has a setting to bypass the VFD dimmer when the lights are on as well. I know the panel lights and actual glass displays dim independently. It will take more research I guess.

 

[Pyro15D]

Small update. I did some experimenting and figured out that in order to give the correct pulse count for MPH, each rotation of the wheel has to put out 10 pulses. It seems like if would be pretty easy to glue 10 small magnets on an axle and then position a small hall effect sensor next to them. I had to do that to my Delorean when I added cruise control to it. They didn't come with cruise control from the factory. This way may end up being a better solution because it doesn't matter what diff ratio you have. The speed will be accurate unless you run different diameter tires.

Another thing I did was change the panel dim wire. Normally, the panel dim wire is tied to the running light circuit. That means, whenever the running lights are on, the panel is dimmed. I like to run with the running lights on all the time. To get around that, instead ran the panel dim wire (blue wire, pin 12 on the 20-pin connector) to a headlight fuse in the engine compartment. Why couldn't I just connect it to something inside? Well because the headlight switch grounds the headlights to turn them on. If you refer to the TEWD here the headlights are always getting fed 12 volts when they are turned on, then the dimmer switch inside just chooses which pin to ground (high or low beam). The panel dimmer takes a 12 volt signal to dim the display. Now the panel stays bright until I actually turn the headlights on.

 

[3p141592654]

Whoa, this ain't no Delorean and you don't need to do that. Just tap into the ABS speed sensor with a high impedance op amp, then a divider as needed.

 

[Pyro15D]

I thought about using the ABS wheel sensors but how many teeth are on the wheel?

I would love to make a custom sensor that just screwed onto the transmission where the speedo cable normally goes. I really don't see a good reason why the cable goes all the way up behind the dash when you could just run 3 shielded wires down to the transmission. I'm sure Toyota had their reasons...

 

[Grandavi]

If there was a way to delete the speedo cable that would be a good thing IMO.

I like how my dodge ram was capable of being electronically setup for a speedo correction when I put on 20" wheels. Wish I could do that to my Supra... Lol

 

[3p141592654]

Assuming the hard part is done (the digidash install), this can be done with a single chip micro, some code and feeding the ABS speed senor signal into its ADC port.

 

[Pyro15D]

Grant, correct me if I'm wrong, but I think the speedometer is driven from the ECU over a bus-type system. Programming the ecu via the OBD-2 port would make that pretty convenient. I need to do that with my larger tires on my Tundra actually! I've just been lazy. Pi, I am actually trying to learn programming with microcontrollers. I bought an Arduino Uno a couple weeks ago and have been going through the projects one by one to learn the coding. Another thought that came to me was using something along those lines with a GPS receiver. I'm assuming the coding wouldn't be too tough to just read the GPS signal and turn it into pulses. I haven't read about interfacing GPS yet however (I'm a big noob when it comes to programming). Plugging in the stock tire size and revolutions per mile gives me 811.32. Move the decimal over 1 because the system reads 10 pulses per revolution and I get 8113 pulses per mile. That should be pretty easy. I almost find that to be the best solution. It would be very easy to program in a switch as well in case you wanted to read KM or MPH. I guess I need to do some more reading.

 

[Grandavi]

On my Ram, they did it through the ECU as far as I could tell. Just entered in a wheel size. Its not exact but very close to correct now (as my wheels are 33.5" high as opposed to the original 27").

I suck at car wiring... lol, so I have zero good info to give.

 

[Pyro15D]

Yeah, that seems to be really convenient. My 05 Tundra is a bit more of a pain in the ass since Toyota has a habit of locking down their ECUs. I have larger tires on my truck as well and I guess I just have to deal with it. Most people install some speedo corrector in the wiring but I hate the idea of installing something additional to take care of what I should be able to adjust myself. I can understand locking down the data that deals with driveability and such but they should know that people like me want a "Man Truck" and are going to customize their trucks to look tougher. Just make it easy on us to change tire sizes!

Anyway, yesterday I discovered something really cool as far as speed inputs are concerned. Like I said earlier, to display the correct speed in MPH, you need to modify the stock sending unit from 20-pulse to 12-pulse. Thankfully, Ford has been using a sensor that does exactly that! The 1994-1998 Mustangs use a VSS on the side of their transmission that ouputs the 12-pulse per revolution signal we need. On top of that, they are dirt cheap! On Rockauto, I'm seeing new ones for under $15. The part number is SC37T. This is what it looks like:


Now, there is a small issue. This is a VR-style sensor. It puts out an AC sine wave. The dash needs a 5v square wave to function properly, so for that you need to make or buy a VR-conditioner circuit. I would buy the Brick VR conditioner/ because it is small and also because it runs on 5 volts. This will convert the AC signal to a more friendly square wave signal for the dash. The convenient thing about running this speed sensor arrangement is that you no longer need to run the speedo cable all the way up and around to behind the dash. You can just run a few shielded wires down to the sensor near the transmission. This is environmentally sealed since it was designed to be used on the transmission. It will handle most anything you dish out.

 

[Grandavi]

I have the Escort Passport Max. In actuality... I don't need a speedo because it shows speed.

 

[Silent Deatz]

Does anyone know where I can get the digital speedometer sensor and the fuel sensor?

Edit: could I use one of these things to get a speed signal for the dash?
http://www.driftmotion.com/Marlin-Crawler-VSS-p/dm693.htm
If I get that right, I should be able to throw 5V in the VSS and get slightly lower than 5V out. That should work right?

 

[Pyro15D]

Man, I haven't been on here in months! Moving and getting settled in took more time than I thought! Anyway, as far as the sensors go, they are close to impossible to get ahold of, since the Japanese junkyards don't think of pulling the speed sensor when they pull the gauge cluster out. In post 42, I detail the procedure to convert your standard analog fuel sender unit to work with the digital gauge cluster. As far as the digital speed sensor goes, you can't use the Marlin Crawler unit (trust me, I tried. At only 4 pulses per revolution, it would be drastically off! The stock one is 20 pulses per revolution. If you want it to read in MPH, you need to find a sensor that puts out 12 pulses per revolution. A couple posts above (post 73) I talk about the speed sensor. Seeing your location, I can only assume you need the speedo to read in KM/H. I did find a few 80's Japanese cars in various junkyards that had digital gauge clusters. I think it was a late 80's Subaru Leone that had a digital dash where the sensor was a 20 pulse per revolution sensor. Nippondenso made the digital clusters in the Leone, XT, and Loyale, so the sensors are all most likely pretty identical. One note of advice though. The sensor on the Supra used a 5v signal and had a built in regulator in the sensor itself. The Subaru one doesn't have that. If you directly hook up the subaru speed sensor to the supra dash, the higher voltage will burn out the sensor and ruin it. You will instead want to run a 150-ohm resistor inline with the 5v input.

Oh, a quick check on ebay for digital subaru clusters found this: http://www.ebay.com/itm/SUBARU-WAGO...Parts_Accessories&hash=item1c4a4174f5&vxp=mtr The sensor is bottom and left of center.

 

[Silent Deatz]

Thank you for the great answer!

 

[Pyro15D]

No problem! I'm here to help! I'm hoping to start building more conversions as things start settling in. The problem is finding female analog dash connectors. I want to make a convenient solution for anyone to use.

 

[Silent Deatz]

Is the Yakazi-Connector-Road a dead-end?

I still can't believe it, I got a speedsensor from Germany

 

[Pyro15D]

Oh nice! I don't know where you can buy them new. I know they are similar to some of the connectors on the car already, like ABS and some others. I think I listed them in here somewhere! I'm on my phone and so I can't find conveniently find it.