To go back to the original question, with regard to various Bicycle speedo options, Ive tried a few, the first two on my Gutzzi;
1> Cateye bicycle wired jobbie, which worked fine for a while but a wire broke internally, and after it not working for a while went 'missing' one night in town.
2> Another wired Cateye that I spilled braked fluid onto and it dissolved
3> A different brand of wired type, which fell apart or failed for no reason after only a short time....at this time I decided a GPS one that I can use on both bikes would be better, so>
4> Garmin GPS 'Edge 200' which came with two handlebar mounts (one for each bike
) but seemed to split the LCD when I dropped it
...(unrelated, but Garmin backup was crap), so....replaced with>
5 > Bryton Rider 100?- basic and USB socket failed but replaced under warranty, had it about a year and a half...fits on the Garmin mounts, but not the other way...(Garmin>Bryton) It stops working sometimes but starts again...just a backup really- is handy 'cos I've set it to Km/h.
NB; Don't really need it now as both bike speedos now function (Original Vaguelia reads +10mph/Smiths Chrono reads -10%
).
Just briefly re; system polarity, I originally had +ve earth, but was too confusing-kept blowing other things up so changed to -ve earth, but I think you also need to rearrange the brush wires in the dynamo-- the gurus can clarify that in a different thread
If I recall GB some time ago talked about installing a small inverter to run a GPS speedo/whereamIagain ?