zbigtim

The "slam panel" was right at $100 plus shipping.

FYI - Just spoke to Tabco to order a rocker panel and was told that the horizontal panel that is just above the tail lights is now available. Not sure what you call it. It is not on the website. The website has not been updated in a long time. I don't think it's available anywhere else. -Tim

Yea, that's what I'm afraid of. I used a 2N3904 with the same values on the resistors and the results are as previously posted. Oddly enough, I don't have any 2N2222s lying around. I used another transistor out of my "NPN" drawer with the same results. I don't remember what the P/N was. Hopefully the issue is with my square wave generator. -Tim

Nice work Xnke! Wish I had access to a lathe and the skills to use it. Hey, You say you had no trouble getting the tach to work with the MS Tach Out. Iv'e got my tach mocked up on the bench, but cannot get the tach to span higher than about 3750rpm without the pointer getting erratic. I'm just using a square wave generator right now, found the scale to be about 1000 rpm for every 50Hz, using a 50% duty cycle. I wonder if I just have a bad tach. Using the circuit in the MS Extra Hardware Manual http://www.msextra.com/doc/ms1extra/MS_Extra_Hardware_Manual.htm#tachoout -Tim

I would agree. I've tinkered with electronics, seems like my whole life, and have always used the proto boards. This was my first attempt at etching my own board, and found it relatively easy. There is tons of info on the web on this topic. I'm pressing on with the mod. I think all the difficult parts have been solved. The next step will be the tach, and I think that is going to be much more straight forward. I think may get more enjoyment out of the problem solving than the actual finished product. -Tim

Did I lose everybody on this mod? Does the extra circuitry make this mod not worth the trouble?

Well, I finally got all the stuff together to make a circuit board. I decided to chemical etch the board instead of photo-etch. The photo-etch process seemed to be more complicated, but I understand is better suited if I wanted to mass produce the board. The board is small enough, I'm thinking of mounting it to the back of the speedometer. I was able to mask the copper layer by transferring a laser printed pattern on glossy photo paper with a hot clothes iron. This picture shows the board after the transfer. After an acid bath, the copper that was left exposed is etched away. After cleaning the mask and soldering the components on the board. I had a little bit of trouble on the soldering because the tip of my soldering iron was too blunt, and the solder could have been thinner. Any extra solder or mis-placement of the iron allowed the ground plane to soak up excess solder. But the solder still did not bridge any of the traces. Whew! This is the top view after the board was completed and tested. Ready for installing in the car and final calibration done with a road test and my GPS.

I think I may try to photo etch a circuit board.

After a lot of discussion, mainly through this thread, I have come to the conclusion that the only way to get the maxima speedometer to work properly is by constructing an add-on frequency converter. In theory, this is very similar to the SGI-5 model made by dakota digital. -The speedometer cannot be adjusted internally. The adjustment solder pads will adjust the pointer but not the odometer. I believe this is so different faces can be used on the same electronics. (K/H vs. M/H, or different max speed). -The 300zx VSS worked very nice mechanically, because is will mount on the existing mechanical speed sensor. I knew there was not a snow balls chance in hell that the speed signal would match the speedometer, but I was hoping it would be close enough that I could change to one of the six different sensors available and make it work that way. It turns out that the speed signal was off by by a factor of .435. So when I was driving at 50mph according to my gps, the speedometer was displaying 115mph! This is way too much to overcome by changing sensors. How the circuit works: The VSS from the 300zx (or any Nissan that I have seen so far) outputs an A.C. sine wave with the frequency proportional to the speed of the vehicle. The LM2907 is specifically designed for this type of sensor. The LM2907 outputs a voltage (DC) proportional to the frequency being produced by the VSS. I have coupled this output to the AD654 via the 10K pot. The pot. works as a voltage divider, so that I can change the full scale voltage going to the AD654. The AD654 does just the opposite of the LM2907, it take the voltage in and converts this to a DC square wave who's frequency is proportional to the voltage on its input. Since the Nissan speedometer will not sense the DC square wave (the input must be A.C.), I used the capacitor/resistor network to AC couple the output to the speedometer. This scheme does not produce a true sine wave but it really does not matter. What matters is that the voltage crosses zero. During my speed trials in the car using my gps unit and fluke multimeter, I determined that the Maxima speedometer deflects full scale (140 MPH) at 309Hz. I also found that the 300ZX VSS would output 709Hz at 140MPH (Mathmatical projection of course). So using a sine wave generator I inputed a frequency of 709Hz and adjusted the 10K pot until I measured 309Hz out. I also checked the linearity by adjusting the input in 100Hz steps and measuring the output. It seems to be right on. Of course once I install the circuit in the Z, I will fine tune the calibration to the gps.

It works! I will explain tonight, but I have to take my daughter to baseball practice right now. -Tim

Thanks Pharaohabq. That would be nice to have access to a rep rap. That would be so much better than trying to cob together a combination of old, new and extraneous parts. I am working on a new timing circuit to "re-scale" the VSS signal from the sensor; should be completed by the end of the week. I do believe the sensor is wired correctly, the wiring is very simple (+12, Ground, and VSS Signal). The VSS signal is referenced to ground and is an ac sine. The difference I guess is the RPMs required to move the mechanical speedometer, and the frequency range required by the electronic ones.

Well, I'm digging this thread back from the dead. I decided I was going to try and finish this up. I have finished the mounting of the speedo in the old gauge cup, wired the old harness to the speedo (plus a new wire from the VSS), and installed the speedo in the dash. I installed the black cog and 300ZX VSS that I bought from rejracer. On the road test, judging from the seat of my pants, the speed indication is about double what it should be. Although it was really cool to watch the speed jump 45 mph from gear to gear and eventually pegging the speedo at about 150mph, I need to adjust the speed signal. If I have time tomorrow, I will go for another drive with the garmin to see what the error really is. I'm not sure what the largest cog is for the speed sensor is, but I doubt that I can double the size of the black one. Side view showing the mounting plate made out of a 4" blank round cover for electrical boxes. The stand-offs are make of plastic wire nuts, cut to the proper heights. I then glued the new mounting plate to the old gauge cup with 5-minute epoxy. This is the new mounting plate glued in place. Day time view. Night time view. I am determined to get this project finished. I promise I won't let this drag out for another 2-years! -Tim

Have you tried the first generation Miata?

Yes, I've been thinking about using a plexiglass plate to mount the gauge to, using the original screws. Then mount the plate to the back of the cup with spacer blocks. The blocks could either be epoxied to the cup or screwed. The plexigalss would give me the ability to mount and wire the gauge back lights in the proper locations to illuminate the clear plastic face backing.

Been talking with Rejracer about the mounting of the gauges in the old "cups", so I thought I would share some pictures and some of my findings. I would also love to hear some input and/or ideas of a few things. First off, there was some concern that the electronics of the speedometer will not fit inside the old cup. If you compare the cups side by side, the original speedometer cup is shallower than the tachometer. On the Maxima gauges the speedometer guts require a deeper housing, so I swapped the cups, mounting the Maxima Tach in the original speedometer cup and vise versa. The mounting tabs and holes are exactly the same between the cups, so I will still be able to mount the gauges in there original position (Speedometer on the left, and Tach on the right). I did have to cut a slot in the top of the speedometer cup to allow the circuit board to protrude past the housing (see pics). I don't think this will interfere with the dash, and plan on using some duct tape to keep dust and ambient light out of the housing. The issue I'm working with now is how to secure the instruments in the cups with the proper depth to keep the gauge faces flush with the bezels. I want to keep the faces flush with the bezel because the faces are backlit, while the originals had a gap between the bezel and face to allow the instrument light "around" the face. I plan on using an additional circuit in between the VSS and Speedometer to do some scaling because I don't want to have to try to find a VSS cog with the right amount of teeth. Also this will allow some adjustment for example if I decide to change tire sizes, or rear end ratios. But, I think it would absolutely be possible to wire the VSS directly to the speedometer and find the correct cog. PICTURES: Tachomter. Mock up mounting. As you can see from the front picture, I need to move the face forward towards the edge of the cup (where the bezel meets). Speedometer. As you can see on the top of the cup, where I had to cut a slot for the circuit board. Speedometer. Also, need some mounting ideas here. I'm thinking of cutting a piece of plexi-glass and securing it inside the cup somehow. As mentioned above, I could use some ideas on securing the gauges to the cups. -Tim