I use to put a schotky (not sure about spelling) diode for spike protection, cathode to positive. Francisco Gustaf J. Barkstrom wrote: >Roland and all, > >Okay, I don't feel too stupid now. I was going to post >a question about separate power supplies, but then this >happened. So, here's my question about power supply >separation: Where is the separation? What I mean is, >I understand using two areas of the board, but do I need >two wall-warts, two regulators, etc? Do I have to separate >them back up to mains AC? > >Yes, I chose the ULN2803A because it has the 2.7k resistors >on input; the datasheets say this is specifically for >5v TTL/CMOS connection, so I thought I was good on inputs. > >Again, I'm using a 15V Zener to pin 10 (common) on the ULN2803 >to prevent back EMF. Is that sufficient? > >Thanks again, > >Gustaf > > > >>-----Original Message----- >>From: pic microcontroller discussion list >>[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Roland >>Sent: Friday, February 27, 2004 7:00 AM >>To: PICLIST@MITVMA.MIT.EDU >>Subject: Re: [EE:] Release of magic smoke >> >> >>The 2803 has a 2K7 series resistor on the input, so that should be OK. >>Whats more likely happening is that flyback from the stepper coils is >>causing the 5V to spike, and the pic is doing the clamping! >> >>try and use separate supplies, as shown in the diagram, or adequately >>isolate the two regions, logic and power. >> >>Regards >>Roland >> >> >>At 02:45 AM 27/02/04 -0500, you wrote: >> >> >>>One of my 16F84A's just died after some high duty-cycle running >>> >>> >>of stepper >> >> >>>motors. The circuit I built is basically the one found at the bottom of >>>this page: http://www.dakeng.com/u2.html Source code is also available on >>>that page. >>> >>>However, I buffered the inputs of the PIC with a 74LS244 (octal line >>>driver), and used a Darlington array (ULN2803) on the outputs to >>> >>> >>drive the >> >> >>>steppers instead of the discretes shown in the schematic. Note >>> >>> >>also that I >> >> >>>am not using a resistor between the PIC output pins and the >>> >>> >>Darlington array >> >> >>>input pins. >>> >>>An ASCII block diagram of my circuit: >>> >>>[parallel port data pin] -> [74LS244] -> [PIC] -> [ULN2803] -> [Stepper] >>> >>>The entire circuit, including motors, is using the same 5+/GND regulated >>>power supply. PIC is RC clocked, and the power/gnd pins are not >>> >>> >>bypassed on >> >> >>>either the PIC or the line buffer/drivers. Pin 3 of the PIC floats, as >>>the page linked above says "leave this pin floating if you like." >>> >>>I ran two steppers (Vexta 2-phase, 5V/1A nominal) on this circuit for >>>several minutes, but no more than 30 seconds at a shot. So, I >>> >>> >>got brave and >> >> >>>told my software to run the motors over a long distance, and they ran >>>continuously for about 4 minutes. After that, the chip froze (motors >>>stopped); held MCLR low and released it high again, still nothing. I >>>touched the top of the Darlington arrays and the buffer/drivers, barely >>>warm. I touched the PIC and about got a 2nd degree burn. >>> >>>I turned everything off, went to bed, and turned it back on the next day. >>>Normally, the motors lock into an initial position at power-up, >>> >>> >>but now no >> >> >>>power is going to either of them. Before I troubleshoot further, I would >>>like to get some input on the flaws of my circuit. PCB art and >>> >>> >>schematics >> >> >>>available at your request, if the flaws of the circuit are not already >>>blatently obvious... >>> >>>I think (in a sophomoric way) that my question is: why is so much current >>>going through the PIC? >>> >>>By the way, the circuit worked very well until I turned up the >>> >>> >>duty-cycle. >> >> >>>Thanks, >>> >>>Gustaf >>> >>>-- >>>http://www.piclist.com hint: The list server can filter out subtopics >>>(like ads or off topics) for you. See http://www.piclist.com/#topics >>> >>> >>> >>Regards >>Roland Jollivet >> >> >>JeM Electric cc >>PO Box 1460 >>Kloof >>3640 >>Kwazulu Natal >>South Africa >>Tel: +27 31 7024412 >>Fax: +27 31 7011674 >>Cell: +27 83 255 6017 >>Email: enquiries@caon.co.za >> >>-- >>http://www.piclist.com hint: The list server can filter out subtopics >>(like ads or off topics) for you. See http://www.piclist.com/#topics >> >> >> > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics > >. > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics