Could I have some advice on Which Pic Please?

[skimask]

Whats the best pic that will do the following:
compatible with a DS18B20 for temperature measurement

It's not the PIC that fullfills the requirements for being compatible with the DS18B20...it's the keyboard operator.

4 input pins (simple high or low inputs)
4 output pins (simple high or low outputs through transistor switch to operate relay)
6 Pins for an LCD (4 bit mode)
gonna be working with an 8Mhz resonator because no crucial timings involved.

http://www.microchip.com/ParamChartS...g=en&pageId=74

A 16F628A handles everything but the 8Mhz (has 4Mhz internal)
Once you need an 8Mhz internal and small, as in 18 pin package,
http://www.microchip.com/ParamChartS...g=en&pageId=74
2 pins power/ground, internal 8Mhz, 14 I/O + a pin for the DS18B20...
18F1220/1230/1320/1330...
No pins wasted...small package...

It's all in the parametric search pages at www.microchip.com

[Ron Marcus]

How much program/RAM space do you need?

[Acetronics2]

Hi, Karen

with the external Xtal or reso ... 16F628/648 will be unbeatable !!!
with internal 8Mhz clock ... 16F88 or 16F819 ...

18F1320 ... I had small problems with mine ( no more than 20 reprogrammings available , EEPROM single location programming ... FALSE !!! Works well ONLY with more than two writings ... )

searchtool here also:

http://melabs.picbasic.com/Scripts/perl/picsearch.pl

Alain

[skimask]

18F1320 ... I had small problems with mine ( no more than 20 reprogrammings available , EEPROM single location programming ... FALSE !!! Works well ONLY with more than two writings ... )

Had problems with my 18F1320's also using a Warp13a awhile back. Had to add an extra .1uf cap across Vdd/Vss, worked like a champ. Have been using PICKIT2 to do them the same way. Haven't tried it without the extra .1uf cap's though. Will do over this weekend and let you know.

[Acetronics2]

Hi, Ski

I've tried Picstart, ICD2, PicFlash and a programmer from one of our Magazines ( a serious one ! Lol ! ) ...

Always the same answer ... only erasing seems to work.

a second chip had refused Picstart programming for a moment ... and with the 8.0 MPLAB release, It miraculously came back to life ...
I didn't insist further and "locked" it firmly on a PCB !!!

Capacitor and/or 1K have been tried with no appearing result ...

Now, I just program them from blank and send the PCB assembled ...

µChip has been unable to tell me something about that ... and the error sheet didn't show anything suspect ...
The memory issue needed to use the Brownout ... very,very bad idea aboard something flying !!!

Alain

[Dave]

karenhornby, I would suggest using an 18F2620 as there are enough pins to do what you want as well as 2 CCP modules a voltage reference, comparator and you can run it at 40Mhz. if necessary. I have used these parts for many products over the last year and 1/2 and have had great success. If you are planning on laying out a pc board it will give you some extra pins to use in the future... It also has 4 timers and enhanced capture/compare for use with an H bridge later on if needed...

Dave Purola,
N8NTA

[karenhornby]

Thanks guys
All pretty helpful, and I never knew abt the reference page to look them up.
The program I've written is 8k (the hex file is) and the reason I havent even considered the 18 series is i was as few pins as possible and dont need any complicated maths functions or add ons. It's going to be a simple switching circuit depending on what inputs are high will then determine what outputs go high and whats displayed oin the LCD display, it's that simple
I actually never considered an internal reference it would cut component count down using internal too thanks
The only problem stopping me using the 16F628A as suggested is the program size, i could add eeprom i guess but it's simpler to use a different pic than use more components.
My idea is to make the project as small and compact as possible but still using discreet components and NOT smd's.

Looks like it may have to be the 16F877A
Thanks Everyone
and Hi Dave, de Karen M3ZZZ