Cleaning up a mechanical VSS signal for the MPGuino
 

As great as the MPGuino is there was one thing that drove me up the wall...

Driving along at low speeds was no issue. MPGuino read nice steady numbers. Get on the freeway and over 50MPH then the issues start... I would be going 110MPH then instantly 70MPH then 30MPH then 80MPH then 100MPH. The data generated was total garbage.

The issue turned out to be this Tracker I have has a mechanical speedometer with a magnetic reed switch to generate the VSS signal to the ECU. All is dandy and peachy at low speeds BECAUSE the MPGuino has a certain amount of filtering capabilities in it's software called VSS delay. However at higher speeds this will do no good because the reed switch bounces so bad it starts to fludder. Increasing the VSS delay can help mask the problem but if you add too much delay it will affect the data.

This calls for a filter circuit. I searched around and found a few threads on it, mostly Geo Metros. Some people suggested a few resisters some resisters and capacitors. I'll tell you what I did.

I took apart an old laptop charger and harvested a small inductor coil and a 3.3nf ceramic ac line filter capacitor from it. I soldered the VSS wire to one leg of the inductor and one leg of the capacitor. The other leg of the capacitor is wired to ground and the other leg of the inductor is the VSS wire that goes in the MPGuino.

My theory is the capacitor is small enough it won't screw with the VSS signal but enough to dampen bounce that occurs. The inductor is to help block any type of ac signals and interference that might sneak their way in to the unshielded wire. Here is a crude diagram...

http://ecomodder.com/forum/attachmen...1&d=1362659316

So far so good. According to the MPGuino the signal is steady up to 65MPH (speed limit on the interstate here....haven't gone faster yet)

Here are the other threads about VSS bounce for your reference...

http://ecomodder.com/forum/showthrea...-vss-6174.html
http://ecomodder.com/forum/showthrea...arm-15980.html



Motor on :turtle:

I get the signal from abs sensor and after 60 mph or 100 kph it gives rubbish information i did set the delay to 1ms but it does not solve my problem , i'll try your method although i would like to wait until you reach higher speeds...

Do you know what kind of sensor it is?

If you can get the parts free like I did it is worth a shot. Unfortunately if I go faster than about 60mph my FE goes to shizzle.... Maybe today on the 70PSL downhill I'll try to give it a bump up to 70ish and see what happens.

You can always glue a magnet to the main shaft and some kind of reed switch close enough to get pulses. You can use bicycle speed sensor even. It's hermetic, reliable and cheap :)

You can always use a simple diode and capacitor to filter signal. Low power diode anode to VSS sensor and 4.7uF 30V paralel to MPGuino. That should filter all the noise.

I'm not sure noise was my issue I believe it was switch bounce. The cap between VSS and ground helps to dampen switch bounce so the MPGuino only sees one edge on each pulse.

If you have access to oscilloscope you may see what's the issue there. But if switch is bouncing that may cause ECU to work incorrectly. Maybe you should take a closer look at your VSS switch.

Guys problem solved , one day I've accidentally removed the power from the mpguino before it saves to eprom and every configuration lost, so i've entered pulses per speed and micro sec per liter that and forgot configure vss delay that was 2ms by default :confused: oooodd... Speed is now right except when i run over bumps and potholes (all the time Greek roads :rolleyes:) , then speed goes instantaneously nuts... That maybe is not a big issue...I'll try your solution, i have a lot of spares from power supplies so...

It shouldn't be like that, with MPGuino going nuts over bumps. Check VSS cables, from the sensor to the dashboard and MPGuino. You've mentioned before that you gest VSS signal from ABS sensor, right? So you should check ABS cables then. But I don't think that plugging into ABS signal is a good idea. You can get some false signals and that can mess up your safety. It's better to fabricate VSS sensor by gluing a magnet to the drive shaft than mess up with ABS. IMHO :cool:.

No vss sensor and cables exist on my car except abs sensors and speed information travels from abs computer through the multiplex network to the whole car , i don't think it is practical to intercept that although i've tried to. Yesterday i've used abs twice due to the heavy raining and it worked perfectly as always. Though my intention is to either put a speed sensor to the gearbox from and older clio2 version of fabricate a sensor as you said but that would be extremely difficult due to the fact that drive shafts are very small and totally exposed to the elements (a belly pan could help a lot)

I think that you have a VSS sensor
http://i11.photobucket.com/albums/a1...8012011675.jpg

It's a Kangoo picture (not mine), but as far as i know Kangoo and Clio have the same engines and gearboxes.