At 07.46 2011.11.13, you wrote: >On 13 November 2011 12:10, IVP wrote: >>> 3) bigger bypass? Ferrite beads? Would they help for the EMI? Sure >>> filtering the power wouldn't help >> >> Feed-through caps and chokes on power and signal lines are common >> in car audio systems to filter out ignition noise. For your application = it >> would be a LPF or BPF based on the duration of the closure >> >> Is it possible to add a low-Z driver down at the reed switch ? Like >> some paralleled low-power CMOS gates ? That would also allow >> you to extend the pulse (eg one-shot), which would help discriminate >> between signal and noise >> >> It can still be two-wire (or one if the frame is used as Vss) by super- >> imposing the closure signal onto Vcc. Or smart switching between >> the line as Vcc to the reed (held up with a reservoir cap) and a >> conditioning circuit for it and then as signal back >> >> Joe >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > >What sort of cable is used to the reed switch? I realise that you >can't change it but you may get an improvement by terminating it >appropriately. If it's a single wire)with frame return) , then there's >not much you but a twisted pair will provide a level of immunity if >operated into a differential detector. Basically the load resistance >and capacitance for both legs should be the same. A simple opamp >configured correctly should be enough. Correct earthing as you suggect >and as much filtering as you can put in will also improve things >significantly. > >RP Thanks for the hint, while it doesn't help for the reed sensor, it helps for other stuff, and for my own culture. So, for example, a reluctor pickup (2 wires, no central ground) can go into an opamp (or should it be an instrumentation amplifier) and common mode noise will be rejected. Which is logical. But the part I was missing is.. without a central ground, will the opamp / instrumentation amplifier detect the differential signal? Imagine I have a INAxxx instrumentation amp from TI, can I connect the reluctor pickup (isolated from the ground) to the - and + inputs and it will work? Before I thought that a ground is necessary even in differential inputs.. was I thus wrong? Thanks, MarI/O --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .