Browsing Posts published in September, 2010

Oh, so nearly there.

The sensing resistor block.

The sensing resistor block.

A pretty momentous week, all told.

To the right here, you can see the resistor ‘block’ of ten 0.1 Ohm resistors prior to soldering which when wired in parallel make an astonishing 0.01 Ohms.  This is before they are soldered.

This low resistance is needed to be able to sense the current flowing into the batteries.  I had been using two 1 Ohm resistors in parallel which gave 0.5 Ohms, but found that when I wound up the power supply, the voltage across them -and hence the amplified voltage coming out of the new current sensing i.c. was a little on the high side -even though the current is meant to be limited to 2 Amps or under.

The bike generator will give out over a factor of ten of this, hence the lower value resistors.

The board in the middle of construction.

The board in the middle of construction.

Here you can see the board ‘as I’m building it’ last night.

On the right, you can see the PIC programming board I built so many months ago.  Towards the top of the photo, you can see the ‘new’ board with the little PIC and LEDs on it.  In the middle at the back, you can see the new 0.01 Ohm resistor block I built up last night.  This has been safely mounted using the engineers favourite -Superglue!

Between the two boards and below the new resistor block, you can see two FET’s that switch the power with signals from my new board.

Luckily, unlike normal bi-polar transistors, FETs don’t go into ‘thermal runaway’.  When this happens, a transistor gets hot, so its resistance goes down, therefore heating it up even further and the runaway happens.  The result? A little plume of blue, acrid-smelling smoke, accompanied by the immortal line, “Whoops.  That’s taken the chill off it…”

FETs are much more graceful when it comes to these vexing problems.  When a FET gets hot, its resistance increases, thereby limiting the current, thereby cooling it down.

SO, I’m using two here in parallel in all confidence that neither will blow, and it means I’ve effectively doubled the current-handling of the switching circuit.



Here we have the finished board.

You can see I’ve mounted the two switching FETs, and if you look really closely, you’ll see they are connected.

Beneath these two FETs is another heatsink with another device on it I haven’t previously mentioned.  This is the final ‘blocking diode’.  This prevents current going backwards into the circuit.  Without it, the cyclist would get a free ride as the pedals would turn themselves.  Not something we are keen to promote!

Anyway, thats it for now.  Wednesday afternoon is a LEAF session and as the weather’s so nice…

Okay, okay…  I can hear what you’re thinking! “When’s he going to get on the bike…???

I’m be leaving early this afternoon, and I’ll come straight back, and yes.  …I’ll get on the bike!

Don’t nag!

A few days sick-leave.

I’m sorry, but I’m getting over a mild case of ‘Cat ‘Flu’, so I’m not currently up to my best.

Alfie's poorly.

Alfie's poorly.

Don’t worry, though.

Just a couple of days after this shot of me on my dad’s bed was taken, I was up and ready for action again.

Of course, it helped that I’d really ‘played it up’ with him; so much so that he fed me loads of good stuff like tinned tuna and salmon.

Hee hee.  I really must remember to sneeze more.  It always gets him going!

Odin training in Water

We have numerous baths at LEAF

This is our Aqua Special Training.  As you may see Odin is sat in a cold water bath, and I think his extremities are getting a little cold, but he is holding up, though looking a little startled.

Strange Sights at LEAF

"Jonny Darko"

Whats all this then ?

Mitsy can ordinarily take things in her stride, but on this day she wasn’t please with the “Jonny Darko”  or Wier Cat that had come to join us, however after a time she realised that it was not a threat.

Kerrrr… -chink!

Now, Dear Reader; that was the sound of a single, solitary penny dropping.

That was the sound (…in my head of course.  Where most of the voices come from these days…) I heard as I realised that I hadn’t set the PIC up properly!

Before you start any fun stuff with a PIC microcontroller, you have to set it up so it knows which pins are mean’t to be doing what.

In this case, because I hadn’t read the manual properly, I’d forgotten all about the two comparator circuits built into these things.  Before you use the standard input/output (I/O) pins, you first have to turn off the comparators, and tell the chip that you’ll be using digital I/O’s.

Then, just to be on the safe side, you should always clear the pins.  -Reset them to zero.  Its good practise, and only takes a couple of instructions.

D’ Oh!

So, my prophecies this morning were right.  A little Plot Work really is good for the body and soul.

Tomorrow, I’m hoping to get a full day at this (…after Blogging some photos on the main Blog of today’s efforts…), so I’ll be sure to tell you all about it tomorrow evening.

p.s. Oh, and on my way out this morning, I happened to meet the postman.  I asked if he had anything for me, and yes, he had!  Two of your finest PIC16F684 microcontrollers, so that now gives me four in total.  Fun!


Thursday was a good day except for the point were we had to dispose of our outside Tomatoes, which had been struck by Blight. Yes we lost them all. On a brighter note a good haul of potatoes from the therapy plot with reds (Desire, don’t think thats correct spelling) and white’s don’t know name but some of the biggest of the harvest.

Our resident Computer (engineer, consultant, etc) has given me a very large memory. To which I’m eternally grateful, so expect more little stories to be bunged up on the metal shed.

Another first was that my eldest daughter visited the plots on Thursday on her quest to gain experience of voluntary organisations. Which see found very interesting, she is at the moment working (volutary) for Health Cross but is hoping to start work with the NHS by the end of the year.

Nick and myself completed drafting plans of the plots and hope to come up with a final rotation for next year hopefully before the end of the year. We are being radical especially with the top plot, mainly getting the strawberries back under control, after all it is our show case, being the entrance to the allotments an all !!

Quick and easy stir-fry.

1 comment


One medium sized courgette, sliced.

Handful of runner beans roughly sliced.

A few button mushrooms, halved.

Three thinly sliced rashers of un-smoked bacon.


  1. Pre-heat a little olive oil in a frying pan or wok to a fairly high temperature on an open fire / cooker.
  2. Throw in the ingredients except the bacon, adding a little lemon and dill flavoured olive oil if desired.
  3. When the courgettes start to get a little colour, add the bacon, stirring continuously.
  4. When the bacon is done to your liking, the dish is ready!
  5. Serve immediately.

The whole meal should take no longer than 10 minutes to prepare and cook, and there’s very little washing up afterwards.

Nick 15/09/10

Just think of a swan.

You’re no doubt thinking we’ve lost it.

Far from it!  No, just think of a swan on a lake, gliding serenely over the still, calm water at dawn on a summer’s day.  You think its so graceful, so elegant, so effortless.  …Well underneath, its legs are paddling like mad!

Same thing here at LEAF.

Yes, there are some days when loads gets done and loads gets reported, and yet others where we go all deathly quiet.

Like the swan, we don’t appear to be doing much -on the surface at least- but underneath, ah, underneath everyone is feverishly paddling and flapping away.

Well, Dear Reader, today has been such a day.  Nothing much apparently getting done, but ‘under the surface’, so to speak, loads of stuff that doesn’t really warrant many column-inches.

Today, a major part arrived for a job for The Chairman, so that was fitted (…it worked!..), then some of the new current monitoring i.c.’s arrived.  Whereas the previous ones only monitored current going one way -into the batteries- these will monitor it going in and coming out at the same time.  This means we will know how much faster we’ll have to pedal when someone switches on a light some other electrical gadget.  They have basically the same pin-outs as the other ones, so only minor modifications needed to the growing, the bulging circuit board being constructed here in ‘Wardian Towers’.

Tomorrow morning before The Plots, I have to go down to Maplin’s to pick up some parts I ordered last week.  These will enable the circuit to monitor much higher currents -the sort of currents produced by a cyclist.

We have an ‘early start’ tomorrow -our first volunteers start arriving just after 10.00.  Then in the afternoon I have to go to a friend’s house to properly sort out the CD/DVD reader and install some applications on his machine.

After that, I’ll be back here and busy with the circuit, and I promise some photos to show the progress made.  The mounting of the 10 shunt resistors that the current is measured with should be worth a giggle, at least.

Haven’t the foggiest what I’m on about?  Ha!  Just you wait and see.

‘Seven Of Nine*‘ would love it.

* ‘Seven Of Nine’ -a character from ‘Star Trek’ ‘Voyager’, but then you already knew that…

Power Update.

For those who just can’t wait!

Quite a lot of running about today (…like a new landline installed here at ‘Wardian Central’ and another visit down to The Quacks…), but inbetween times, I’ve had chance to do quite bit on the power control circuit.

The board is sprouting components.

The board is sprouting components.

If you click a couple of times on the photo to the right here, you’ll notice that the board has ‘grown’ some new bits.

I’ve put another 1 Ohm resistor in parallel with the one stood upright.  This is to effectively double the current measurement range.

I’ve also added a 100 Ohm 3 Watt ‘dummy load’ of the white resistor laid down on its side on the right beneath the red and green LED’s on the right hand side.

Today, I’ve been taking meaurements from the new chip I put in -the current monitor- and checking them against the formula given in the datasheets.

It turns out I’ve blown one of these chips, but thats not a problem.  I have one spare and four more on order and they should arrive by the end of the week.

So, now I’ve got the remaining working chip in place with revised and added-to code in the PIC, everything appears to be checking out okay.

The PWM (Pulse Width Modulation) part of the PIC is working pretty well -there’s just a couple of bytes to change, and its switching between PWM ranges as expected.

When you first turn the circuit on with the power supply giving out zero volts, and as you’d expect, nothing comes out of the circuit and the tell-tales are not lit.

As you turn up the voltage, you reach a point where the green one lights and the PWM kicks into action.  As you increase the voltage, the green tell-tale goes out and the red turns on, and at the moment, the PWM waveform reduces, but this is simply a ‘stupid’ in the coding that I haven’t yet been bothered to put right.  No worries!

Anyway, Dear Reader, I’ll leave it there and carry on.

p.s. And the new ‘Toys’ are brilliant!

This Saturday’s Pickling

Hello Guys & Dolls,

             Pickling got cancelled last Saturday, but will be on the 18th Sept (Saturday) all things being well, the weather that is. We have had a contribution of beetroot from John. We have plenty to pickle it will be after lunch around 2pm onwards.

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