-----Urspr=FCngliche Nachricht----- = Von: "Jose Da Silva" An: "Microcontroller discussion list - Public." Gesendet: Freitag, 03. Februar 2006 04:27 Betreff: Re: [EE]: ? to circuit design > On February 2, 2006 02:03 am, Enrico Schuerrer wrote: > > I try to design for model railroad an automatic terminal loop switch > > (for analog model railroad). When I searched the net I found > > different layouts for this purpose but all designs I found are for > > NMRA DCC. In this case the DCC signal is a floating square wave > > signal with around 15ms cycle duration which delivers the coded > > information and the energy for operating the locomotives. > > > > I attached a part of this layout - what I couldn't understand is the > > part with Q1 and Q2, the anti serial switched MOS-fets BUZ 10. From > > the functionality it is clear that a small PIC (12F629) do the job - > > if there is to much current T2 will send a Low-signal to the PIC and > > via T1 the MOSFets will switch off. > > > > Is anybody please so kind and help me what is behind the layout with > > Q1/2. > = > Q1/Q2 is acting like a sensor to test for when the DC motor brushes = > make/break contact. This gives a pulse signal back to the PIC chip to = > tell the PIC how fast the electric motor is turning, and therefore it = > basically tells you how fast the locomotive is running. > = > Your simplified DC-out is between the collector of Q3 to the DC-out pin. > All this extra stuff (Q1,D1,R3,Q2,D2,R2.... is a sensor circuit). If you = > want to leave it out of the circuit, your circuit will still run okay, = > but you will have no pulses to report back to pin RA3, and therefore no = > real-time knowledge of true speed. > = I'm afraid that isn't the point... Q3 is to measure the output current - .7= V over base/emitter will give a signal to the PIC to switch via Q1/Q2. = The problem is (was) why Q1 and Q2 are anti serial in this configuration. Thank you for your help Enrico -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist