Thanks, and it's a very very clever circuit, but I wonder if I can omit the capacitor will the bias create problems on the reluctor pickup? I'm afraid the capacitor will create a timing/phase shift between the two pulses, varying depending on the frequency/RPM. The negative pulse happens 30 degrees before the positive one, and that this relationship holds is critical for the project. Even one single degree of shift will cause proble= ms, that's why I'm afraid of using a input capacitor. On the other hand if the input is biased, the pickup will be affected in that other way. :-/ At 22.52 2011.09.08, you wrote: >You could try the circuit attached to this message, it worked well for me. > >Isaac > > > > > >Em 8/9/2011 13:39, Electron escreveu: >> Thanks, but the impulse will be very similar to half sines, first negati= ve >> then positive. Duty cycle of input signal is like: >> >> 3% negative half sine, 4% zero volt, 3% positive half sine, 90% zero vol= t >> >> frequency of this whole cycle will be ~ 10Hz to 250Hz >> >> timing precision is extremely important, that's why I think I must use a >> couple of transistors per part of pulse detector, to get very sharp edge= s >> at the output. >> >> One thing that worries of my design is that it feeds back about 440mV at >> the pickup, which is an inductor and will probably not like it. I can >> bypass with a capacitor, but then the timing will be affected. :( >> >> Perhaps I should really use the "emitter to input, base to ground and >> output from collector pulled up" scheme like on the URL link above, so >> I get rid of the capacitor (not shown in my schematic), but then I will >> have to add a 3rd transistor.. :( Ain't there a way to get a good gain >> from the "emitter to input, base to ground and output from collector >> pulled up" solution? That stage has no gain at all. >> >> Cheers, >> Cesare >> >> >> At 16.36 2011.09.08, you wrote: >>> On Thu, 2011-09-08 at 15:45 +0200, Electron wrote: >>>> Hi all, >>>> I need to make a circuit that will let my PIC digital pin detect if >>>> an input signal (from a reluctor pickup) is smaller than about -2.0V >>>> >>>> Power supply is single and +5V. >>>> >>>> I have designed my own circuit, using just one transitor biased this >>>> way (file my-circuit.GIF in attachment). >>>> >>>> However on the Net I found this other circuit: >>>> http://www.transmic.net/XR400/use_negative_first.jpg >>>> >>>> I have simulated it, and I think it's inferior than mine in all regard= s >>>> (uses two transistors rather than one, edges are not sharper, etc..). >>> You mention it's a negative "pulse". In that case if you are really >>> starved for parts you should be able to get something working without >>> any transistors. >>> >>> I just tried a quick sim with something that you might be able to fine >>> tune to work for your particular situation (you didn't mention the >>> negative pulse width, duration or frequency, so I've made assumptions). >>> It uses 2 resistors and a cap. I've attached a screenshot of the sim. >>> >>> TTYL >>> >>> >>> >>> >>> --=20 >>> http://www.piclist.com PIC/SX FAQ & list archive >>> View/change your membership options at >>> http://mailman.mit.edu/mailman/listinfo/piclist > > > >--=20 >http://www.piclist.com PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .