Joe, I may try that, once I separate the power supplies. I may also use a regular diode as opposed to the zener. I know, "regular diode" is probably laughable to some of you, but that's what I'm calling it until I learn better. :) Wow, what a learning experience this is, too. Starting to think I should drop the hobby and just go back to watching TV. Gustaf > -----Original Message----- > From: pic microcontroller discussion list > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Joe McCauley > Sent: Friday, February 27, 2004 10:24 AM > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [EE:] Release of magic smoke > > > Tie pin 10 to the positive supply of the motors directly. > > Joe > > -----Original Message----- > From: pic microcontroller discussion list > [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Gustaf J. Barkstrom > Sent: 27 February 2004 14:35 > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [EE:] Release of magic smoke > > > 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 > -- 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