Re: [mowbot] mowbot brains

Lawrence Lile (lilel nospam at
Mon, 3 May 1999 08:37:58 -0500

-----Original Message-----
From: Byron A Jeff <byron nospam at>
To: mowbot nospam at <mowbot nospam at>
Date: Sunday, May 02, 1999 2:06 PM
Subject: Re: [mowbot] mowbot brains

Hear Hear, I second everything you said avout PICS. I'm probably going to
build my mowbot brains out of a PIC16C505. I've got a few (a key point - "a
part in hand is worth two in the catalog") They are a very inexpensive chip
(US$0.90 for 1, $0.50 for 100,000) and look like they have enough I/O.

To the fellow using 555's - Microcontrollers are pretty complicated to
learn. That's why they are so much fun. You're learning curve will be
easiest if you go with one of the PIC basic add-ons. OTOH, if you ever want
to make a living programming microcontrollers, study assembler. It is not
that hard to pick up.

>I'm a PIC guy. They've been my uP of choice for the last 4-5 years. Here
>1) Relatively cheap. PIC16F84's are $6 and change at digikey. The 8 pin
>PIC12C508 are less than $2 in singles.
>2) Extremely simple instruction set. Only 33 instructions. One can learn
>whoule set in an afternoon.
>3) Cheap programmers and development tools. Microchip, the PIC manufacturer
>give away their Windows based assembler and simulator, and their programmer
>is less than $100 and programs everything. If you really want to do it on
>the cheap a 16F84 programmer can be built for less than $10 and an
>I'm a Linux guy and there's a development push for assemblers and
>for the Linux environment. One of my students put together a 16C84
>that runs like a champ. The 16C84 is simple because it's EEPROM based so
>it doesn't require the eraser, timing, and voltage, that EPROMS require.
>of the other PICs are EPROM based.
>4) Lots and lots of expertise. There's a extermely active PIC mailing list
>and a GNU based PIC software mailing list. Hobbists, professionals, and
>authors frequent these lists.
>5) They're tough little buggers. Can source/sink up to 25ma per I/O pin,
>have internal protection diodes, a watchdog timer, and can even survive
>reversed polarity on its power supply pins.
>6) A wide range of parts. From 8 pins with internal oscillator to 68 pins
>with 1K of RAM and 16K of program code space. There are a wide range of
>peripheral choices. Each has one timer, many have 2 or three. Some have
>serial interfaces, others have A/D (even the 8 pin parts), compartors,
>timing capture pins, syncronous serial interfaces are all available.
>7) Power miserly. Runs in the microamp range at 32khz and in the single
>millamp range at full speed.
>8) And lastly they are faster than bats out of hell. Unlike Intel's 8051
>series, the instruction rate is clock rate/4 not rate/12. So a 20 Mhz part
>is clicking along at 5 million instructions per second! And all straight
>line instructions run in 1 cycle, with branches/skips clocking in 2 cycles.
>There are other manufacturers in the game, like Atmel, Zilog, and Motorola
>which are currently in a price war with Microchip. But until I need
>100,000 parts, I'm sticking with PICs
>Using them are simple. Attach power and a crystal or resonator. Will even
>with a RC clock if timing isn't critical. Program the part, and off you go.
>You'd probably want to start with the 16F84. It has a EEPROM program core
>words), 64 bytes of data EEPROM, 68 bytes of ram, 13 I/O pins, and an 8 bit
>timer. That should be enough to detect all your bump switches, drive
>your relays (via a trasistor driver, 25ma usually isn't enough to kick
>a coil.) and determine how long to delay with more than enough horsepower
>to do a few other tasks. BTW I drive relays using an optoisolator...
>Hope this gives you some insight.