Using the PicAxe chips
Anyone who has visited this site will
know how much I love these little PicAxe chips, but
what is a picaxe, and how do you get started.
First up, how did I get started on
I had read about them a few times in SiliconChip magazine, but never took the plunge and bought one as
they weren't available locally. But about 3 years ago
I was wandering around the local Dick Smith electronics
store and saw a Basic Stamp starters kit. It was on
sale for $50, and included a BasicStamp
2, prototype board and manual. So I bought it, took
it home and started learning about these little computers
on a chip.
||The Basic Stamp 2 includes
a micro controller, ROM and RAM chip. It comes with
a software package you install on your computer,
the software used to program the chip.
I connected a couple of LED's and little
Piezo speaker to the outputs, and within 30 minutes
I had the thing flashing lights and beeping. Good fun.
The Basic Stamp only had digital inputs, so could not
measure voltages directly ( Though I did work out a
RC network to measure analogue inputs ). And they were
I read about the PicAxe chips in Silicon
Chip, and discovered they had true analogue inputs plus
a more powerful range of commands, so I ordered in a
18A PicAxe chip from Oatley
Electronics, and since then have also added a 28X
and several 08M chips to my collection. They are cheap!
The 08M is only about $4, and a 28X cost about $25.
So how do we use a PicAxe chip?
Easy. The PicAxe chip is a microprocessor
with built in flash ram, digital and analogue inputs,
internal watchdog timers, and digital outputs. The little
chips are pre-programmed with a boot loader program,
which lets it talk to your computer via a serial cable.
On your computer you use a program called the PicAxe
Programming Editor ( which is free to download from
their web site at http://www.picaxe.co.uk/ ).
The Programming Editor lets you write a program
for the PicAxe, then with a mouse click you upload this
program into the PicAxe chip. The PicAxe has a flash
memory, so it will remember the program even when the
power is turned off. The "Language" used is
a simple version of the common "Basic" programming
language, anyone with experience in Basic will pick
up this dialect easily.
The Basic Circuit.
To connect up the PicAxe we only need
a simple circuit.
This is a PicAxe 08 chip.
This circuit is all we need to get a PicAxe working,
though with nothing connected to the other pins it wont
be very useful. On this chip we have 4 spare pins, and
we can access these pins in the PicAxe program. Say
we connected a LED and 330 ohm dropping resistor to
Pin 6 ( In/Out 1 ), then then wrote a program on out
PC like this
|This program will set
output 1 (Pin 6 on the chip) to high (5v), wait
1000 mili seconds (1 second), set pin 1 low (0 volts),
wait 1 second, and then go back to the start, and
endless loop that will flash our LED on and off
every 2 seconds.
Once we upload the program
with the run button ,
the PC will copy the program into the PicAxe. The PicAxe
will now run this little program, in fact we can then
disconnect the PC, and whenever we power up the PicAxe,
it will run this program. In effect we have used the
PicAxe chip like we would use a old NE555 timer IC.
We can also look at pins
to get info into the chip. A switch could be connected
input 3 (Pin 4), and the PicAxe software could be written
to check the status of this switch. The PicAxe can also
read in analogue inputs, like measure a variable resistor
or voltage, then act on this. ie if a voltage on input
1 goes above a set value, switch off pin 2.
There are dozens of commands
we can use, letting us read in analogue values, send
serial data back to a connected PC ( like the PicLog ), drive mosfets and LCD displays (Charger),
measure time delays and frequency, PMW output, etc,
etc. If you download the PicAxe editor program, you
get a bunch of PDF manuals that describe in detail all
the commands, plus show you how to connect different
devices like motors and relays to the PicAxe.
In summary, the PicAxe
lets you replace a handful of components with one little
chip, which is easy to program. And the big advantage
of a PicAxe is it can be reprogrammed thousands of times,
so you can reuse you circuit for different applications.
For more info, visit the
PicAxe web site http://www.picaxe.co.uk/,
buy yourself a little 08M chip for a few dollars and
get into it. Once you've started with PicAxe chips you
wont look back. In Australia the PicAxe chips are available from...
Also worth checking out the Australian OzElecForum.com