On Mar 28, 8:50 am, vasile surducan <[email protected]> wrote: > On Sat, Mar 27, 2010 at 9:46 AM, mattschinkel <[email protected]>wrote: > > > I have changed my ICSP schematic many times to try to suit others. No > > matter what I do, someone will not be happy. As you can see, nobody > > can agree one one schematic and I am still having trouble! > > Don't be upset Matt, you're doing a great job. Remember that everything you > do is for you, not for me, Mike or Joep, nor even for the readers of your > tutorial. I know this is difficult to understand right now (and also weird), > but will be easier after some time will flow through your hear. So what you > have to understand is only for you, it really does not count what any of us > says here. > > Reseting via capacitor, button and serial interface is OK, althought is a > concept of multipurpose which is not necessary in a teaching board like > jaluino (which, btw stinks for many reasons I'm bored to explain here). > > When you connect a button directly on a reset capacitor assure the energy > stored in the capacitor will not produce flames on the button contacts, > which can kill the MCLR input. That means adding a small discharge resistor > (100 ohms or so) in series with the reset capacitor is a good practice. > Vasile yes, though for very small capacitors <= 100nf, may be not needed.
A pair of diodes to supply and ground would clamp the RS232 A transistor may have a 5V zener voltage on Base/Emitter. So this is why transistor driven by 1K to 10K resistor from RS232 has a diode from ground to base to clamp the -3V to -25V spec of RS232 to -0.7V. You'll find that not only do transistors turn on at about +0.65V on Base, but may ALSO turn "ON" at -5V on base. Also it's bad practice to rely on diode clamps inside ICs as they generally have very poor current capacity compared to external 1N4148. It's not to hard to have working Hardware. It's a greater skill, knowledge and experience to have "correct" Hardware that will work on all conditions. You definitely would never bother with a series resistor on a switch shorting a 100pF capacitor. You definitely *WILL* on a switch shorting a 1000uF capacitor, or it will have a very short life. 100nF with 5V is maybe OK. 100nF with 220V needs a resistor. Energy = 1/2 * C * V^2 ... so 220V isn't 44times, it's 1936x the energy the switch has to cope with. I don't think the RS232 reset is so good without a little further thought! While you my not read Vasile and I agree all the time, the differences may be mostly due to Language and thinking of different special cases (My native is not English as UK speaks it but Hiberno - English) . He is obviously very expert and experienced, http://en.wikipedia.org/wiki/Hiberno_English -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
