Vdo Speedometer Pulse Calibration
Arnaude Kubiak
DIAGRAMF (right)
The display lists the auto-calibratemode as AUTOCL; the pulse-per-mile mode as PULSE; and the reference/fine-tunemode as ADJUST. When you see the method you wish to use, let go of thebutton and that function will be enabled.
3. Drive the reference distanceof one mile (or 1 kilometer). NOTE: As you drive this distance, the speedometerneedle will not register or move. This is a normal occurrence during theauto calibration process.
4. When you have gone exactlyone mile, press the button again. If the electronic impulse rate detectedby the speedometer's microprocessor is within the calibration range limitsof 500 to 399,999, the rate will be shown on the LCD display. For example,your reading might be "P16000 ^ Calibration Range 16000). Such a displayindicates that the impulse rate detected during the reference mile youdrove exactly matches the microprocessor's programmed rate for 1 mile.That means the speedometer is now perfectly calibrated to provide the mostaccurate display possible of both speed and distance. The speedometer finishesits Auto calibration by moving the pointer through a full sweep, then backdown to zero. However, if the speedometerdetects any kind of error during your run, the LCD will display the following,"P00". This means no useable impulse was detected. In this case, simplyturn off the ignition, and start the process again.
If you know the exact calibrationvalue for the vehicle and type of sensor you are using (pulse-per-mileor pulse per kilometer), you may use that value to manually calibrate thespeedometer.
To calibrate your VDO Speedometermanually:
2. As soon as you see theword "PULSE," release the button. After a few seconds, the display willstart flashing a series of numbers (factory default setting) that you canchange to represent the correct calibration impulse value. For example,a number like 50000 will show on the display, with each digit flashingin turn, except for the last digit on the right, which is fixed: first,the second 0 from the right; then the third 0 from the right; then, thenext 0; and finally, the 5th.
3. As each number flashes,press the button to change it until the correct digit appears (that is,the number you wish to input). For example, let's say the number that representsthe correct calibration value for your vehicle and sensor is"43850." Whenyou begin the manual calibration process, the LCD displays a default value.Each digit, except the one farthest to the right, will flash, in turn,from right to left. Wait until the second digit from the right starts toflash again. When it does, press the button to start cycling through thenumbers available for this digit. When the number "5" appears, releasethe button.
At this point, the number"5" is set, and the digit to its immediate left begins to flash. Pressthe button again, and hold it till the number "8" appears. Release thebutton. Now, the second digit from the left begins to flash. Again, holdin the button until the number "3" appears. When it does, all but the left-mostdigit are set. Repeat the process to set the "4" and the value in our exampleis set. The value"43850"should be displayed on the LCD readout.
4. When you are satisfiedyou have properly entered the correct calibration value - when that valueis displayed on the LCD readout - take your finger off the button and wait.After a few seconds, the value you have entered will be downloaded intothe speedometer's microprocessor, and the speedometer, will revert backto normal operating mode. At this point, the manual calibration processis complete.
In the future, you can usethis method to update the calibration value stored in the computer shouldit ever become necessary. This function also allows you to manually adjustthe calibration value after you perform the automatic calibration process.
Youcan fine-tune the calibration of the speedometer's analog display (thepointer showing miles-per-hour or kilometers-per-hour) by using speed testequipment and the "ADJUST" function on the LCD readout. The pointer canbe repositioned anywhere within the calibration range of the speedometer.See DIAGRAM I below. To manually calibrate the pointer on the analogdisplay with the car on a dyno at the specified speed):
3. When either "UP" or "DOWN"is showing, press the button again, and hold it in. If you hold the buttonin for just a short time, the pointer will move slowly either upwards ordownwards, depending on which mode you selected. This allows for a veryaccurate adjustment of the pointer. Holding the button in for a longerperiod of time makes the pointer move faster.
4. When you have repositionedthe pointer where you want it, release the button and wait. If no furtheradjustments are made within one minute, the speedometer will revert backto the normal operating mode.
NOTE: If you move the pointerpast the upper limit of the calibration range, the LCD display will flashand you will only be able to adjust the pointer downward. If you move thepointer past the lower limit of the calibration range, the LCD displaywill also flash, and you will only be able to adjust the pointer upward.
The later digital mileageVDO speedos can certainly develop anomalies. Most often a replacement isless frustrating and cheaper than attempted repairs. However, VDO willcheck it out for you for free if you indicate that you will be purchasinganother if it turns out bad. If they find nothing, then take thetime to locate the little capacitor behind the speedometer. It is verysmall and hidden in a wire shroud. This capacitor can become defectiveand will have the speedo give bizarre readings. Replace it, it only costsa few dollars.
VDO SPEEDO LCD SCREEN ISSUE
When using the AutoMeter GPS Module to drive your AutoMeter electric speedometer, the only time that there is no calibration required for a speedometer is when you are connecting to an AutoMeter speedometer that has not yet had a previous calibration attempt. In other words, when both the speedometer and the GPS module are new, out of the package, there is no calibration required as they are both calibrated the same from the factory. If someone has already attempted to calibrate either the speedometer or the GPS module previously, then calibration of the GPS module, to speedometer is required.
Calibrating the GPS module-to-speedometer is very easy. First, you turn the power on and then push and hold the only button on the GPS module. After a few seconds of this, the pointer on the speedometer will start to climb. The longer you hold, the faster it climbs. Stop holding when the pointer on the speedometer reaches 80. We suggest stopping around 70, then using a series of momentary button pushes. You are now done. It will time out after about 4 seconds and the pointer will go back to zero.
If you experience erratic or jumpy speedometer behavior (especially at low speeds), then power the speedometer on, and watch the LCD display on the speedometer. It will show the current PPM (pulses per mile) for a second or two, then will default to the odometer. If the PPM is quite a bit less than the factory PPM of 16000, then recalibrate both. Here is how:
If the above is successful, but you still have a little spike or bounce at a very slow speed, then go back over the above, but double the pulse count to about 64000 pulses (32000 ppm) during speedometer calibration and then recalibrate the GPS module again. The higher pulse count is basically increasing the speed signal frequency resulting in a smoother signal.
Does the GPS seem to take a long time (as in minutes) to latch onto the signal? First, move the antenna if not already outside or near a window. Second, ask if there are any other active GPS items in use. GPS Navigation, something radio related, another speedometer (not likely, but had to throw that in there), or anything else. GPS signals can disrupt each other and compete for a signal if the antennas are too close. During earlier testing, I experienced this and was amazed how much better they responded when I separated the distance between the antennas. I was testing two interfaces, the built in GPS speedometer, and had the navigation system on, with all antennas on the dash. Nothing was happy!
The best location to mount the antenna is outside. Inside near any window, the top of the dash, window frame, package tray, etc. are all good spots to mount as well, but not as good as outside. The antenna is waterproof and you can paint it.
If you have a VSS signal from a transmission or any 2-wire sender (i.e SN96, SN95), make sure you are using the SN74 with switches 1-4 OFF (2 may be ON if you are experiencing interference) and have the speedometer dip switches set to 5 6 7 8 OPEN.
The pushbutton does not move very much when pressed making it hard to tell if you are actually getting the pushbutton to work. If you are having troubles calibrating, make sure to press the pushbutton extra hard to insure it is making contact.
A common mistake is a customer will enter calibration mode to set the speedometer and then start the engine. When this happens, power is cycled and the speedometer is no longer in calibration mode. (It is possible to calibrate the tachometer without engine running) The pushbutton must be pressed until the engine is started (if not a few seconds after). Once the engine is started, the pushbutton can be released.
If, during a measured mile speed calibration, the speedometer pointer is pointing at 30mph, no signal is getting to the speedometer. Check the signal. If it is at 45mph and you are NOT moving, it is getting interference from somewhere.
A mag sensor signal may or may not require an interface box, depending on how many pulses per mile it is producing. If the signal is less than 6000 or more than 10000 pulses per mile, they will need a SN74
If SN16 is being used, test by turning shaft with a drill to see if speedometer responds. The signal can be monitored by connecting a multi-meter set to DC volts between the signal post and ground post of the speedometer. With power to the speedometer ON, slowly turn the shaft of the SN16. The voltage should alternate from battery voltage and zero volts. If it does not alternate, then the SN16 is bad.
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