We're supposed to get problems onto the forum for all to see and help but I've got two newbs who didn't get answers and are shy about trying. I've talked one onto the sensors forum because my ability to help has run out and I'd like to feel better about his chances of success.
I think that English is not his first language, which doesn't help. But at least he tries things. http://arduino.cc/forum/index.php/topic,153374.0.html
What he needs is advice on running an Allegro gear-tooth counter off car 12V. I dunno if it should have a regulator but at least I've got him ready to put an opto-isolator between it and the Arduino.
The other posted last year and got zero replies. I dunno if he'll be back.
Was it on the English side, or on a more specific language side?
One thing that is a turn off is when a newby writes in such a manner that it would they would appear to be expecting someone here to drop everything and solve their problem for them. Or the question they ask is so vague that one really has little clue what is being asked for.
The other thing that can happen is that they posted on a busy day and dropped to page 2 of that topics threads. I don't often look past page 1 unless I am looking for a specific topic. When I have posted the topic has generally stayed on page 1 for a couple days and by the time it has dropped off page 1 I pretty much have an answer.
If your friend didn't post the info on the data sheet he might have gotten ignored because those posts tend to look like someone trying to get the forum to do his homework, and after a while posts that look that way are easier to ignore. May not be their case, but I know that that is how I think.
Need to let them know that they need to do the research work for us. Kind of like the poster needs to do the background work to "earn" other folks time helping them.
A 12V device like that might work OK with a simple voltage divider. Just make sure the grounds are tied together.
Been here long enough to know those points. I will add: Some days I've got time and energy and some I don't.
The one I got to post in sensors just needs a look that he's not about to fry everything. I helped him in PM's to find a sensor (tried to get him to make one, hehehe, learn some physics and save $) and introduced the idea of optical isolation for the Arduino but I can't say I'm an expert at any of this and especially what car power may throw it.
If he can wrap this up then Arduino gets another happy supporter ready to take on new projects.
The other may have gotten back, one Jack_Aubrey. He's making a button panel and I've already suggested a much simpler way, ie multiplex pullup rows and columns that selectively ground rather than HIGH through resistor-per-button (>50 buttons) and some other bits. Well, my way the circuit drawing doesn't look as impressive....
I hope he returns.