Marc, My question was not about the diode bridge but about the reversed diode connected between the input and output of the voltage regulator. Tal > -----Original Message----- > From: Marc Nicholas [mailto:marc@geekythings.com]=20 > Sent: Sunday, June 15, 2003 8:13 PM > To: PIC list; Tal > Subject: Re: [PIC] 16F84 reading 2 digits from serial port >=20 >=20 > Tal... >=20 > It's for reverse current protection. Imagine you have one of=20 > those RadioCrap multivoltage wall-warts and you set centre=20 > pin to the wrong polarity...you run the risk of frying stuff. >=20 > The diode is like bypass capacitors -- A Good Thing=81.=20 > Circuits might well work without it, but for the sake of a=20 > few cents, you may as well protect your investment in parts. >=20 > -marc >=20 >=20 > On 15/6/03 21:49, "Tal" wrote: >=20 > > Jinx, > >=20 > > What is the purpose of the diode parallel to the regulator ? Is it=20 > > necessary ? > >=20 > > I used three terminal regulators for years without a=20 > parallel diode.=20 > > Is it a serious mistake ? > >=20 > > Thanks, > >=20 > > Tal > >=20 > >> -----Original Message----- > >> From: pic microcontroller discussion list=20 > >> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Jinx > >> Sent: Sunday, June 15, 2003 4:48 PM > >> To: PICLIST@MITVMA.MIT.EDU > >> Subject: Re: [PIC] 16F84 reading 2 digits from serial port > >>=20 > >>=20 > >>> Can you specify the @ 9.8304MHz when you buy the PIC? > >>=20 > >> The 9.8304 is just an example of a hex value crystal. I=20 > normally keep=20 > >> 1/2 dozen values in stock - 32768Hz, 3.2768MHz, 9.8304MHz, 10MHz,=20 > >> 18.432MHz and 20MHz and buy others as needed. If one-offs then=20 > >> somewhere like Radiospares, or a local wholesaler for quantity > >>=20 > >>> I was using the PIC basic compiler to program the PIC. > >> Which program > >>> can I use to create HEX for the assembly below? > >>=20 > >> It was written/compiled using MPLAB/MPASM > >>=20 > >> Please change previous PortA definitions to - > >>=20 > >> #define rs porta,0 ;LCD RS > >> #define en porta,1 ;LCD enable > >> #define rw porta,2 ;LCD R/W > >>=20 > >> As I said, the program was cobbled together from other working=20 > >> programs, and there may be the odd small error like this > >>=20 > >> As for the timing, 9.8304 will get you exactly 1 minute intervals=20 > >> with Timer1 free-running > >>=20 > >> (9830400/4) / 65536 =3D 37.5 rollovers / sec =3D 2250 (08CAh) / min > >>=20 > >> You could either enable Timer1 IRQs or poll TMR1IF (without IRQs=20 > >> enabled), then use a 2-byte counter to count 08CA=20 > rollovers. A 32kHz=20 > >> xtal could be used on Timer1 instead for 0.5 rollovers/sec, 30/min > >>=20 > >>> What about the circuit and additional components that I > >> need, can you > >>> help me with this? You mentioned that you have a circuit=20 > where this=20 > >>> PIC can work. > >>=20 > >> Components not shown on this diagram are the capacitors for the=20 > >> MAX232 - you can find connections in the MAX232 pdf. > >>=20 > > http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1798 > >=20 > > To protect the regulator from reversed supply and shorts add the=20 > > diodes. Not actually necessary to make the circuit work but=20 > one silly=20 > > mistake can be costly. The bridge means you can use any old=20 > plug-pack=20 > > with either polarity. Add a filter cap after the bridge > > (470uF) if it's an AC o/p plug-pack > >=20 > >> The only issue is the LCD. I wanted to use two of the=20 > LSD40165-20 to=20 > >> show the two digits. This will allow people to see the number at a=20 > >> distance > >=20 > > 4" 7-seg LED ? Hmmm, big ;-) > >=20 > > http://www.elexp.com/a_data/08lsd40165-20.pdf > >=20 > > Ah, that's a completely different ball game to an LCD. The=20 > circuit for=20 > > that is a little more complex. I'd suggest an MC14543 (BCD to 7-seg > > convertor) and a current sink chip (one of the ULN 2000 range for=20 > > example. Or, as the current is in the low 10s of mA=20 > "possibly" you may=20 > > be able to do this with the PIC itself, but I'd recommend the PIC=20 > > driving a grounding transistor for each segment. You'll find LEDs at > >=20 > > http://www.piclist.com/techref/io/led/pic.htm > >=20 > > Keep the LCD circuit though, it'll come in handy one day, betcha > >=20 > > -- > > http://www.piclist.com hint: To leave the PICList=20 > > mailto:piclist-unsubscribe-request@mitvma.mit.edu > >=20 > >=20 > >=20 > > -- > > http://www.piclist.com hint: To leave the PICList=20 > > mailto:piclist-unsubscribe-request@mitvma.mit.edu > >=20 > >=20 > >=20 >=20 > =20 > -------------------------------------------------- > Marc Nicholas Geekythings Inc. C/416.543.4896 > UNIX, Database, Security and Networking Consulting >=20 -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu