[Sussex] A Little Hardware Help

[Al Bennett]

Hi Steve

(If you'll forgive an interruption from an ex-regular now north of the 
border!)

The 16F628 is a good choice to start with, I've played with them in the 
past (but if you're not too invested in PICs my personal favourite is 
the Atmel AVR series as there's excellent open source compiler (eg GCC) 
and toolchain support).

Do you have a multimeter?  If so, check your supply is giving +5 (+/- 
half a voltish) with respect to ground.  If it's ok then you've excluded 
that problem, just make sure you have the polarity right.  If not (or 
you don't have a meter and want to guarantee a good supply), a 7805 is 
the bullet proof, old school, piece of cake solution.  The circuit on 
this page is what you need:
http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html

You may find the 7805 advertised with extra letters in the part number 
(LM7805, 78S05 etc) but it should be widely available (Maplin, Rapid 
Electronics et al).

Start with illuminating an LED using the micro, then flash it on and off 
(the microcontroller "hello world") before moving on.

Basic things to check:
- Fuses / oscillator configuration (if you're using the internal osc 
make sure it's enabled via the fuses, if you're using an external 
resonator make sure it's hooked up correctly (with caps for two pin 
resonators))
- Check your reset pin (MCLR) is pulled high (through a 10k should do)
- Port direction settings (make sure your outputs are outputs)
- Output port set to whatever "on" is (if you're sourcing current it 
needs to be high, sinking current low)

The struggle is always getting an LED to blink, once you're that far 
things become a lot easier!

Hope this helps, feel free to contact me offlist if you want.

Al


Steve Dobson wrote:
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> Hi All
>
> I've been a software engineer for the 30 years, but I now find that I
> want to learn a little hardware too complement it.  Computers are only
> useful (fun) when the are doing something.  And being able to physically
> interact with the world around them is an area I would like to explore -
> just for fun you understand.
>
> To that end I've started playing around with the PIC16F628 [1]
> micro-controllers - a small but complete computer on an IC.  I also
> found a nice set of hardware & software tutorials [2] to learn from and
> have bought some breadboarding hardware to play with.  My first goal is
> to get the PIC to control a seven segments display (common anode) and to
> that end I have built a simple circuit[3] based on the main board [4].
> Unfortunately my first attempt doesn't work!  :-(
>
> If I remove the IC and jumper the -ve line to the seven-segment display
> lines then the LEDs light up - so that part appears correct - and it
> matches the circuit in the tutorial [5], although as I have a single
> digit seven-segment display I have connected the 8 pins of the PIC to
> the 8 inputs (seven segments + decimal point) of the display and omitted
> the transistor parts.
>
> I guess that the problem lies in the power input to the chip.  I'm using
> a Bandridge BE-516 mains transformer (regulated) to provide the power,
> but do I need any form of circuit on this supply, and if I do what?  Of
> course I am completely clueless at this point as to how to find out what
> is wrong.  I know the PIC isn't blown because if I place it back in the
> programming/test board it works there perfectly.
>
> Any and all help gratefully welcomed.
>
> Steve
>
> [1] http://ww1.microchip.com/downloads/en/DeviceDoc/40300C.pdf
> [2] http://www.winpicprog.co.uk/pic_tutorial.htm
> [3] http://www.syscall.org.uk/simple-circuit.jpg
> [4] http://www.winpicprog.co.uk/pic_tutorial_main_board.htm
> [5] http://www.winpicprog.co.uk/pic_tutorial_7seg_board.htm
> [6] http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/1023
>
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