When I performed my motor swap in my e30, the stock gauge panel just wasn’t going to work for my needs. In the process, I lost the stock speedometer. I thought it would be interesting to “grassroots” a speedometer. In industrial motor control applications, magnetic pickups are used to monitor electrical motor or shaft speeds. The outputs of the sensors can be fed into digital rate indicators, which are scalable readouts to provide feedback information for the operators or technicians. The benefit for my use is that all the electronics and everything I need is in one small package and cheap (mine was $20 plus a few bucks shipping) to acquire from Ebay.
The picture of the readout is not the best. The numbers when lit are very defined and clear, not fuzzy as the picture would suggest.
There are different models available, sizes, and other manufacturers. I chose this particular Red Lion APLR – 6 digit rate indicator model - because it was cheap ($20) and available at the time. It also had the option of powering the unit from an 11 to 14 volt dc source, perfect for an automotive electrical system. I am not sure where to mount at this point. I may remove one of the ac vents (no ac in the car anymore) and fabricate a finished flat panel in its place. I also thought about relocating the headlight switch, removing that switch panel and mounting the unit in its place. Currently, I have it resting in the bottom of the glove box until I decide where it would look the best (least ghetto)
Face plate is a little less than 2” wide by 4” wide. Panel Mount. I will remove the face plate bezel and paint it all black and reinstall; do not like the chromed plastic outline. You can change the decimal point position. All the specs can be found here:
http://www.redlion.net/Products/Groups/Archive/APLR/Docs/03002.pdf
The speed sensor in the GM 5-speed tailshaft (which is now running in my e30) is a magnetic sensor reading a 40-tooth (I believe) gear. The beauty of these rate indicators is that they are scalable for different input frequencies (sensor wheels) and output readings. The stock speed sensor in the BMW rear did not provide a sutiable signal in my case.
It was very easy to wire. The magnetic sensor on the tailshaft has two wires that should be connected to the signal terminal and the ground terminal respectively on the back of the unit using a shielded cable. I already had some cable from another project but I believe you could find it at the local Lowes or Home Depot. A shielded cable will have a foil liner wrapping the conductors or wires. The foil blocks stray RF and other electrical noise to maintain a clean signal from the sensor. Ground the shield on only one end of the cable. The 12 volt source was chosen from an ignition powered circuit. The unit will not lose its settings when powered down. A chassis ground was connected to the ground terminal.
The time multiplier is the setting that compensates for the input signal vs. the output reading on the led’s. The dip switches on the back of the unit changes the time multiplier. They are additive meaning each switch turned on adds to the total of the rest that are switched on. There are equations, in the document referenced above, to calculate the proper settings of the dip switches to yield the desired output. But it is just as easy to switch a few on and hit the road and calibrate. I would suggest following someone maintaining a steady speed in a safe area. I would highly suggest letting someone else drive the car while you adjust the switches. If the reading is too low, increase the time multiplier, if the reading is too fast for a given speed, decrease the time multiplier value. You should be able to enter any value by choosing only those switches and numbers that add up to the needed total. At a given point add up the “on” switches to obtain the total value. Compare that against the readout speed vs. the actual speed and chose (a simple percent difference calculation should get you close) another total time value based on this. This is easier than just randomly turning on and off switches. Keep in mind this value will be different depending on the placement of the decimal point selectable from the dip switches on the side of the unit.
Another advantage of these rate indicators is that if you change tire sizes or rear end ratios, the speedometer can be re-calibrated easily.
Again, this is one unit that will work. At least thus far it appears to work well for me. There are other options out there, smaller units, different type of readouts, etc. that may better suit your needs. I am not an expert here, but there is plenty of information on the internet.
Slick. You can sometimes find Red Lion (or other brand) counters at surplus stores as well. You know, Alpina made a digital gauge cluster that went in one of the dash vents, you could maybe use this for inspiration.
