Post by thread:[EE]: ? to circuit design

part 1 827 bytes content-type:text/plain; (decoded 7bit) 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. Thank you! Enrico part 2 26116 bytes content-type:image/jpeg; (decode) part 3 35 bytes content-type:text/plain; charset="us-ascii" (decoded 7bit)

{Quote hidden}>-----Original Message----- >From: spam_OUTpiclist-bouncesTakeThisOuTmit.edu [.....piclist-bouncesKILLspam@spam@mit.edu] >Sent: 02 February 2006 10:04 >To: Microcontroller discussion list - Public. >Subject: [EE]: ? to circuit design > > >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. The reverse series connection is done to control current flow in both directions, i.e. when you reverse the train the polarity changes. With a single MOSFET, the body diode would always conduct in one direction so the MOSFET would be unable to control the current. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

-----Ursprüngliche Nachricht----- Von: "Michael Rigby-Jones" <Michael.Rigby-JonesKILLspambookham.com> An: "Microcontroller discussion list - Public." <.....piclistKILLspam.....mit.edu> Gesendet: Donnerstag, 02. Februar 2006 11:37 Betreff: RE: [EE]: ? to circuit design > The reverse series connection is done to control current flow in both directions, i.e. when you reverse the train the polarity changes. With a single MOSFET, the body diode would always conduct in one direction so the MOSFET would be unable to control the current. May I please add a second question... If polarity is always the same (like on normal analogue operation only 0 - 14 V DC) on these rails, is there only one MOSFet necessary ? Enrico

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. Hope that explains it. cheers!

-----Ursprüngliche Nachricht----- Von: "Jose Da Silva" <EraseMEDigitalspam_OUTTakeThisOuTjoescat.com> An: "Microcontroller discussion list - Public." <piclistspam_OUTmit.edu> Gesendet: Freitag, 03. Februar 2006 04:27 Betreff: Re: [EE]: ? to circuit design {Quote hidden}> 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 - .7V 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