PIC a ProjectPIC a ProjectThis is one of three files listing student projects: PIC projects | Student Projects for Leeds University | Student Project Suggestions
This page used to be on the CREG web site
The Arizona Microchip 'PIC' range of microcontrollers are useful for a wide range of applications, several of which have been featured in the CREG journal. Here are a few ideas that have occurred to me recently [December 97], and on which I have done some preliminary work. I am considering producing a 'generic' development PCB to cover these and other possible applications - if you are interested in the board, or the projects, please contact david[at]caves.org.uk.
I have also discussed other projects such as
Development boards for the PICs already exist, of course, and their big advantage is that you can be fairly sure that your circuit will work when you first build it. Putting together a strip-board project with a PIC is fiddly, and you waste time debugging the hardware when you should be concentrating on the software. Ive got a couple of strip-board PIC circuits in front of me now and they are forever failing due to the birds nest construction techniques I use (well, Im not the neatest of constructors)
So why do I want to produce my own development board, if they already exist? Well, it will be tailored specifically for the above applications (or some of them, anyway), which require extra parts on the board. But note that, because the board is a development board, suitable for testing a wide range of projects it is, of course, ideal for none of them; and it would not be appropriate to use it for the final version of your project.
Because I will be getting only a small batch of PCBs made they will be expensive - perhaps £50 each (which is roughly what you might pay for a commercial PIC development board). Obviously the cost depends on how many people want a board - it could be lower than this.
You might be wondering why I dont get some home-made boards done at a fraction of the cost. Well, its possible, but personally, Id rather pay to get it done properly, than spend time fiddling around making the boards myself. Solder-resist and a legend are useful too.
Please note that I will be supplying the boards only - not the PICs and the software! Ive no idea when I'll get round to doing even a small fraction of the projects listed above - but perhaps we can share software and exchange ideas once we've got the boards made. All of the above projects should be of particular interest to cave-electronics/communications enthusiasts and some of the projects are quite novel and significant!
If you are interested in buying a development board off me for £50 (or perhaps less) please contact david[at]caves.org.uk - and say how much you're prepared to pay, if you like. There is no commitment on your part. What you'll get will be :
What you wont get are:
The Plessey SL621C AGC Generator was sophisticated but is now obsolete. It was intended for monitoring the audio output of an SSB receiver for which it generated a control voltage to feed back to the RF amplifier (SL610 etc.). It operated using five time-constants, arranged so that it would attenuate noise spikes, but would track the audio. When the audio disappeared, it remembered the AGC setting for a while.
These functions can be implemented in a PIC. The on-chip ADC monitors a rectified and smoothed audio signal and the processed output drives a DAC to adjust the signal gain using an iterative feedback path. This method should allow you to achieve the wide dynamic range needed in an induction radio. You can see an example of this in my cave radio design in journal 30. This solution uses, say, 3 ICs and some Rs & Cs which, although a bigger footprint than a discrete solution, does allow a very sophisticated range of control. The same device could be used to generate squelch and vox signals for automatic Tx/Rx switching.
I have described a speech processor (journal 12) which Bill Purvis experimented with (journal 19). This could be implemented in a PIC, with the addition of external ADC and DACs. A circuit and a software flowchart appeared in an earlier article (Gibson, David (1991) Speech Compressor, Electronics World & Wireless World, Sept. 91, p757.). The technique is supposed to be particularly good at enhancing the conso-nants in speech, and therefore making it much more legible in high-noise conditions. I will be discussingthe technique at a conference in Australia in February 1999.
Truly waterproof switches are difficult to come by. I am not normally in favour of 'jury-rigging' components, but for a waterproof switch, I think there is some mileage to be had in the following scheme. The metal cap off a small jam-jar or drinks bottle (44mm dia.) has a useful 'snap' to it when pressed. Mount a small magnet on the inside of this and bond the lid to your equipment case (glue, bolt, clamp or whatever). On the inside of the case you mount an analogue (not digital), hall-effect sensor. The PIC powers the sensor on low duty cycle (say 0.1% of 100ms) and takes a reading. It self-calibrates to work out the values for 'button pressed' and 'not pressed'. It can also convert the momentary nature of the switch to any number of latch / double-click / time-out / power-down functions. The switch has no physical contact through the casing and so it cannot possibly be a source of a leak.
Using a simple push-to-make switch you could implement an 'intelligent' cap-lamp switch. This is one that you might think is 'over-kill' - so treat it as a design exercise, rather than a useful project! The software state diagram - which can actually be quite complex - is described in my article in journal 33. The operation can be described as follows:
Since the above notes were published in journals 30 and 32 only four people have contacted me to say they would be interested. At the time, I considered that this was not enough to make PCB production worthwhile (but see below). The idea of a general-purpose board was possibly flawed - after all, I did point out that the board would be ideal for none of the projects. Im grateful to Rob Gill for pointing out that Elektor (a UK/European electronics hobbyist magazine) is selling PIC boards for under £15. However, these do not seem to be suitable for my projects, as they are a bit too basic. Martin Melzer introduced me to a European company that produces cheap PCB prototypes www.pcb-pool.com. This makes the PIC project more feasible, so I am now re-considering it.