The scene:- Its very late at night.  In fact, its so late, its early.  Outside, the rain is lashing down and the wind is howling like a banshee.

Apart from the occasional flickering street light, all is dark and quiet, save for a random car going up or down the road.

Thankfully, the cat is out.

Our intrepid engineer is hunched painfully over his desk, his back aching, his fingers raw, his eyes red and bloodshot, straining to see the screen and the dials and displays on various scientific-looking equipment.  Various flashing red and green lights and tell-tales show that his equipment is all up and running.  Just.

The computer is whirring away to itself, happily dreaming computer dreams in ones and zeros.

The engineer mutters something inaudible, scratches his head absently, then reaches for his calculator:

“Right, with 19.5 volts going in at a three percent duty cycle, that means there should be approximately 0.585 volts across that resistor…  …Okay.  What does it read?” he feverishly whispers to himself.

An expectant hush descends on ‘The Lab’ as he rapidly scrabbles for the leads to the probes, selects the right reading for the digital meter and places the probes across the resistor…

…There are a couple of ‘bleeps’  as it auto-ranges, then…

“WHAT?” He jumps up and shouts. “0.596 volts???  You are KIDDING ME!!!”

He quickly turns off the programming board and the power supply, then quickly adjusts the code on the screen.

“Okay.  Lets make it the same voltage but this time with a 4% duty cycle…”

His fingers fly as he re-writes and saves the code, ‘Quickbuilds’ it, then flipping to another screen, loads in the Quickbuild, erases the PIC processor, compiles the new code then ‘flashes’ the code into the PIC.

“Should be 0.748 volts,” he mutters. “0.748 volts or I’m dead…”

He turns on the programming board which powers his board, turns on the power supply and winds it up to 19.5 volts output…

“…EEEEeeeuuurrrrgggggghhhhh!!!  Who’s CAT!!??” He exclaims. “0.789 volts!!!”

Nick's workbench.

Nick's workbench.

The circuit is working well within tolerance.

The resistor is not getting hot, and there are no tell-tale plumes of acrid blue smoke that have, up until recently, figured such a large part of his ‘efforts’.

And so, eyes smarting and dry, nearly closing of their own accord, our Intrepid Engineer decides its Time To Call It A Night.

A last cup of tea, then off to bed, there to lie awake for hopefully just a short while, a huge grin on his face, to wait patiently for The Sleep Pixies and their sprinkling of Magic Fairy Dust.

Tomorrow…  …Tomorrow he will mount the bicycle and pedal like mad, fully confident that he won’t have to replace the fire extinguisher he bought a short while ago.

His neighbours will be safe, and the battery will be charged.

Of that, he is certain.