SERIN in acii, hex, decimal?

[Archangel]

All right Jason,
Grab that data sheet, it's right there under the table leg, open it up to section 9.2.2, you will find a nice little chart, and schematic. That chart will tell you the caps need to be in the range of 15 to 30 pf, and will recommend higher capacities make the oscillator more stable but delay it's start up. . . Please download it (the data sheet) and look this over. That said, most use 22 - 27pf, or resonators as they are easier to mess with. Reading the data sheets are a must, you will understand them more every time you do, and they are free.

[sccoupe]

Ok, with your help and a little from the data sheet , I ordered some 3 pin resonators at 8mhz and they work fine. Everything works at 9600 baud and all. I hook this project up to my car (ignition on, engine not running) and it works as it should. When I start the car, the display goes crazy with all kinds of numbers. This is what happened when I tried reading an analog voltage using a picaxe. It worked fine on the bench, but didnt work with a running car. I even tried a battery for power and only hooked up the serial line and a ground. Can a schmit trigger be used on a serial line? I can only think that there is too much noise on the line. I can hook that line up to hyperterminal though and it works fine. Any thoughts?

Jason

[Archangel]

Ok, with your help and a little from the data sheet , I ordered some 3 pin resonators at 8mhz and they work fine. Everything works at 9600 baud and all. I hook this project up to my car (ignition on, engine not running) and it works as it should. When I start the car, the display goes crazy with all kinds of numbers. This is what happened when I tried reading an analog voltage using a picaxe. It worked fine on the bench, but didnt work with a running car. I even tried a battery for power and only hooked up the serial line and a ground. Can a schmit trigger be used on a serial line? I can only think that there is too much noise on the line. I can hook that line up to hyperterminal though and it works fine. Any thoughts?

Jason

Thinking out loud . . . serial data is a train of 5v pulses, so I would try putting a small value capacitor across the serial input line and bypass the power bus at the PIC too, it may help to shield the circuit in a grounded metal box too - automotive can make tons of RF especially from the ignition system. Even worse if you have a defective ignition wire as you might have 60000 volts going nowhere. A small value choke in series with the input might help too.

[sccoupe]

I just got this thing working. The interference that I was looking for wasnt there. I hooked up the scope looking for noise and realized that I wasnt looking at a TTL signal. After some research on how exactly rs232 works, I found that a Max232 chip was required for the conversion, luckily a guy at work had one. So, Im going to order some 16F688's so that the built in uart and internal 8mhz crystal minimize my components and get the job done.