Overview of the PICAXE - The Tinkerers' Delight

copyright, Peter H. Anderson, Baltimore, MD, Jan,'04, Sept, '04


This discussion focuses on the PICAXE Stamp like devices developed and marketed by Revolution Education in the United Kingdom. I have tinkered with the PICAXE-18X on and off for some nine months and consider the PICAXE to be a tinkerers' delight. Particularly for those tinkerers on a budget.

The prices are very low; about $10.00 for an PICAXE-18X which has a capability comparable with and in many cases more powerful than the $49.00 Parallax Basic Stamp 2. The 18X goes beyond the Basic Stamp 2 to provide a number of 10-bit A/D converters, the ability to read from a Dallas 1-W DS18B20 thermometer, interface with many devices using the Philips I2C protocol, true PWM and infrared remote control. The latest PICAXE-08M with 256 bytes of program memory provides similar capabilites for nominally $3.25.

I believe that Revolution Education is subsidized by a utility in the UK and most uses tend to be educational, used by senior level high school students in Australia, New Zealand and the UK.


With the Basic Stamp, the user edits, compiles and downloads a program. The download is really "tokens" which are stored in an outboard EEPROM (24LC16B). The Basic Stamp processor (PIC16C57) then fetches each token in turn, decodes it and executes the instruction, and then returns to fetch the next token. The Basic Stamp also includes a voltage regulator and a clock.

The PICAXE uses much the same technique, except that the tokens are stored in the same PIC processor which accommodates the download, reads, interprets and executes the tokens. In most cases, the PICAXE uses the PIC's internal clock and there is no on-board voltage regulator. Rather, the user provides +5 VDC and GRD to the PIC. Revolution Electronics tends toward battery packs, which may well be easier in a class room. My recommendation is to use a 7805 voltage regulator in conjunction with a nominal 12 VDC wall power unit.

Rev-Ed uses a PIC12F629 (1K word) for the PICAXE-08. The "monitor" program uses all of the flash memory and the tokens are stored in the data EEPROM (128 bytes). This will accommodate about 30 lines of Basic code and this may well be quite adequate in realizing simple designs where you really don't care to dedicate a $49.00 Basic Stamp or BasicX BX-24. The cost of the PICAXE-8 is about $2.00.

The new PICAXE-08M uses a PIC12F683 (2K words). The monitor program uses all of the flash memory and your program is stored in EEPROM (256 bytes). It is about $3.25.

The PICAXE-18 has gone through a number of iterations as the Microchip flash PICs have become increasingly powerful. The original PICAXE-18 uses a PIC16F627 (1K) and uses the 128 bytes of data EEPROM to store the tokens. The PICAXE-18A uses a PIC16F819 and features a number of 10-bit A/D converters and uses the 256 bytes of EEPROM for storing the tokens.

I opted to jump in with the PICAXE-18X which uses a PIC16F88 (4K flash memory). The added memory permits the monitor to be accommodated in flash program memory while leaving 2048 words for the user's program. The data EEPROM may be used data storage.

There has been a similar migration path with the PICAXE-28, -28A and 28X. With the 40-pin PIC, there is only the PICAXE-40X.

With the PICAXE-08 and the PICAXE-18 versions, the PICs internal clock is used. With the 28 and 40 pin versions, an external resonator or crystal is required.

Development Platform

The PICAXE Development Software is available as a free download from the PICAXE web site. A development board of some sort is required and I prefer a solder less breadboard. As previously noted, a source of +5 VDC is required. A serial cable and two scaling resistors (10K and 22K) are required. All of this is very low cost. I sell a complete assembled development system for nominally $40.00. When compared with a Parallax Board of Education, this is a real Cadillac system at much less than half the price. If you burn out a PICAXE-08 or 18X, it is not a matter of shelling out another $49.00. Rather, probably something less than $10.00.

Rev-Ed does offer Starter Packages. For example the PICAXE 18 Starter Package include a PICAXE chip, a circuit board with a ULN2803 octal driver, a battery box, a serial cable and a CD. Its a good buy, but it has limitations. As with most software, the software on the CD is most likely many revisions behind the latest. The PICAXE-18 starter package is shipped with the PICAXE-18, not the -18X. The battery box accommodates four AA cells and I don't like supplying the PICAXE circuitry with anything as high a 6.0 VDC. As of this writing, there is no schematic for the circuit board and it is definitely motor oriented with no prototyping area. But, in all fairness to Rev-Ed, their audience is high school students and I can attest to the fact that motors catch kid's imaginations. However, if you are interested in tinkering with the PICAXE for other applications, my suggestion is to skip the Starter Package and simply buy the PICAXE chips, download the software, get some kind of +5 VDC power arrangement and a serial cable.

The Target Audience

Recently, a Basic Stamp user was only too happy to share his unhappy experience with the PICAXE on the Yahoo Basic Stamp Group, He had used the battery connector to attach a 9 VDC battery to the PIC, the CD was broken and the documentation was scattered all over the place. This was eagerly joined by the bash bash by Parallax. But, then a few folks spoke up for the PICAXE. By morning, the posts had been deleted and I assume those who posted the positive, joined me in not being able to post anything. Parallax has now pulled their news group back to their website.

My point is, the PICAXE is not a Basic Stamp where people have been writing application notes for well over a decades. In many respects the PICAXE is far more powerful, but it has its downs as well, and my feeling is it is not a wise choice for an absolute newcomer without guidance. It is for more advanced tinkerers. Although applications for the Basic Stamp may well be rewritten, the PICAXE is definitely not for the user who only wants to "plug and play". That is, not for the impatient who desires to only take some Basic Stamp code and attempt to compile it using the PICAXE editor and whines when it doesn't play.

I have been programming for a very long time on many many platforms using many languages. However, in Jan, '04, I spent a very happy week, on and off, developing various applications for the PICAXE-18X. Yes, I can use a two point thermistor model to calculate temperature using the natural log function on a BX-24 or PIC16F877. But, there is a certain intellectual satisfaction in using 8-bit table lookup with a linear interpolation and realizing this with less than 400 words on the PICAXE-18X. This leaves some 1600 words for other applications.

For the user with patience, the PICAXE may well be the final development platform. That is, use the Basic Stamp or BX24 to develop an application and then map it over to the PICAXE for the final application. You may wish to control a fan in the attic, measure temperature, relative humidity or atmospheric pressure or develop a device which responds to a Sony remote control but you may not wish to throw a $49.00 BS2 or BX24 at each application.

One very big advamtage of the PICAXE is that it uses standard PICs and thus, general purpose PIC prototyping boards developed by Olimex and others are readily available in realizing a final product.


In fact, the documentation the PICAXE site is very well done. I studied the Basic command summary and looked for samples using "Google". There were not all that many. And, I tinkered, trying this and that. After all, each "try" is not like rewiring vacuum tubes. Rather, type a few lines and try to compile. Eventually, I would clear one hurdle and approach another. As each hurdle is cleared, it is cleared forever.

There is a Yahoo PICAXE group, but I have learned much more at the PICAXE Forum. It is quite active, and I like the format of "grouped by topic" better than Yahoo. The user "Technician" knows his cookies. I have noted that most realistic questions get answered, either by another user or by "Technician". I can't avoid saying this. There are those who need help and those who can give help. Resolve to become one who can give help and do so.

My Commitment.

Shipping from the UK is rather expensive. You may order five PICAXE-08's for less than $10.00 and find the shipping is an additional $20.00. At some threshold, the shipping goes to $40.00.

I plan to import and resell the PICAXE-08, PICAXE-18X and PICAXE-28X on something close to a revenue neutral basis. That is, no profit. However, I cannot provide technical support. Support is available from the PICAXE forum and usually the best support is an inquisitive mind. Yours.

I do not plan to import other circuit boards, cables, and other accessories.

However, if you are a school in the United States, I recognize that it may be difficult for you to send a purchase order to the UK. Contact me (pha@phanderson.com) and I will import whatever you want.

I plan to continue selling the Development Platform using the large solder less breadboard which is described on my main PICAXE page.

I also plan to begin selling Olimex PIC prototyping boards (18, 28 and 40 pin) with a second female 9-pin DB9 solder cup connector and the resistors in kit form. This will allow the user to develop the application using the solder cup connector and then perhaps remove it. These boards have a large prototyping area, an onboard 7805, a power connector and a MAX232 interface. (Note that the fixed DB9 connector on these boards interfaces with the MAX232 and because of the logic inversion, it can't be used by the PICAXE software to download the tokens. Thus, the second temporary DB9 connector.)

I will continue to develop applications as I have time.

I also plan to continue having a number of my undergraduate seniors, who have a very firm grounding with the far more sophisticated BX24, develop applications for the PICAXE. Some might argue that good education would be moving on to an exotic 32 bit processor, but my feeling is it is equally good education to move from a processor where things are easy to a processor which requires a good deal more critical thinking, let them figure out what are important sample routines to illustrate concepts and write the application notes.

Happy Tinkering!