Van: Goovaerts Aan: PICLIST@MITVMA.MIT.EDU Onderwerp: Hardware scheme Datum: donderdag 10 december 1998 22:02 Hello Glenn, > Does anybody know what the values are for the following components (Look at > attachement to see the schematic --> RS232-I2C interface !) > Probably all the VCC's in the picture are +5V ? Yes. It's the output of the 78L05 voltage regulator ... > 1. Power supply area : D1, Z1, VCC (up right in picture) > D1 --> probably 1N4148 (Casual diode) ? Could be something heavier. It should be good for 150 mA (max current for a 78L05) Maybe a 1N4001. > Z1 --> ? Equal to the maximum supply voltage of the 78L05. It protects agains over-voltage and swapping the Plus/Minus wires. It should be a sturdy one. Maybe a fuse between J2, Pin1 and the Diodes should be in order. A 12V bulb 0.5 A would doo to. It should only light-up if something goes wrong. Talking about making the circuit Fail-safe ... Whow ! > VCC --> +5V ? See above. > 2. I2C area : R2, R3 and VCC (up left in picture) > R2 --> Think it's 4,7k ? > R3 --> Think it's 4,7k ? Is O.K., but 10K will work as good. For short-ish wiring > Both with VCC = +5V ? VCC == VCC :-) (see answer on first question) > 3. Oscillator area : Y1, C7, VCC (down right in picture) > VCC --> 5V ? VCC == VCC (I'm hearing an Echo ...echo... echo ... ;-) > Y1 --> 20 MHz !!! In picture 8 MHz crystal is used. > Think thats important to choose C7-waarde ? > C7 --> ? C7 is for the de-coupling of the Pic's supply voltage only. It has got nothing to do with the crystal. > 4. VCC (down left in picture) > VCC --> +5V ? VCC == VCC (Can we make a song with this as the center-point ) > By the way : is this a Power On Reset scheme. > I have been told that you have to do this with a RC-filter to ensure > that the reset pulse is long enough to actually reset the PIC ! ? > Others told me to connect Vdd with MCLR with or without a resistor > in between. What do I have to do here, and what are the values for > R,C and VCC ? A power-on reset circuit is build-in into the Pic. An external Power-on reset is only needed when the voltage rise-time is slow. On the subject of pulling-up the MCLR with a resistor : The book say's that it's good against ESD & EOS (Electro Static Discharge & Electrostatic Overstress). But I don't know. I myself just connect it to VCC. You could do it with a resistor if you are thinking about ISP (In System Programming : Programming a PIC when it's allready soldered onto the circuit-board). > Probably a lot of my questions you ask yourself why in godsname am I > asking this. Please be patient with me. I'm a beginner, but I'm learning > much and fast ! A year ago I knew nothing about PIC-controllers, Now I'm "the master of the Universe" Quoted from somewhere : "Jesterdaj I koeld not write PIK. Now I am writing ... ehhh.. Stuff for it !" > Thanks for your time. > > Hope I didn't make anybody mad because I'm sending a picture. But its a small one. If you would not have supplied it I could not have given you the answer you are getting now ... Just don't send big ones. > Hope to hear from you soon. > Glenn Goovaerts ! And I am Rudy Wieser Greetings & welcome.